BI 331 OSU (All Quiz Questions)

What determines the maximum frequency of AP generations in a neuron?

The duration of the absolute refractory period. Right! Since the absolute refractory period dictates that no other APs can be generated during that time, the longer the absolute refractory period, the longer the neuron must wait between successive APs and the fewer APs that can be generated in the time frame.

Synovial fluid: - is used by some cells to make ATP - is located within intervertebral discs - is produced by chondrocytes - is found in synarthrotic joints

Is used by some cells to make ATP. Right! Synovial fluid is made by the fibroblasts in the synovial membrane (a loose type of connective tissue called areolar). The synovial fluid provides nutrients to cartilage cells which they use to make ATP. Chondrocytes do no make synovial fluid though they are fed by it. Intervertebral discs contain fibrocartilage not synovial fluid. Synarthrotic joints include joints like the suture, synchondrosis and some types of sydesmoses. They do not contain synovial fluid.

Big graph. Above is trace of the transmembrane potential of a neuron taken at single location in the neuron. Each number refers to durations between the successive dashed lines. The graded potentials are due to one type of ion movement.Using the big graph above, which of the following is TRUE about the trace above?

all these traces were recorded on the axon membrane Right! Each graph (set of axes) shows transmembrane potential at a single place on the neuron. Because this trace shows action potentials, we must be at the axon - only the axon can generate APs due to the presence of voltage gated channels at that location. We can also generate graded potentials on the axon - these occur due to nearby channels opening and ions diffusing towards the axon. Notice that the depolarization of #2 was below threshold and did not trigger an AP.

In the normal 30 year old skeleton, osteoclast activity is matched by osteoblast activity. What would happen if osteoclast activity was greater than osteoblast activity? - The bones would become weaker. - The bones would become stronger. - There would be no effect on the skeleton.

The bones would become weaker. Right! Osteoclasts break down bone (chew it up), osteoblasts build new bone. Since bone is continually remodeled by constant action of the osteoblasts and osteoclasts, if the osteoclasts are destroying faster than the osteoblasts can build, the skeleton will become weaker. This is exactly what happens in osteoporosis.

During development, if a problem arises with the ectoderm, which of the following would most likely be affected? - Skeletal muscles - The brain - Bones of the limbs - The lungs

The brain. Right! The ectoderm gives rise to the brain. The other three are derived from the mesoderm.

What is directly preventing myosin from binding to actin? - Troponin - Actin - Tropomyosin

Tropomyosin. Yup. The image shows tropomyosin covering the myosin binding site. It must move to allow actin and myosin engagement.

This image is of a skeletal muscle cell (myofiber). What is the sarcolemma? - cytoplasm - cytoskeletal protein - cell membrane

Cell membrane. Right! The sarcolemma is the cell membrane of a muscle cell - "sarco" means flesh (meat, muscle is meat) and "lemma" means husk or outer coat. The cytoplasm of muscle cells is called the sarcoplasm The cytoskeletal filaments of muscle are actin and myosin

The growth plate between the epiphysis and diaphysis of a long bone is functionally classified as ____________ and structurally classified as _________________.

Synarthrotic, cartilaginous

The Joint between the teeth and the jaw bone is functionally classified as ____________ and structurally classified as _______________.

Synarthrosis, fibrous

The calcified suture lines between flat skull bones is functionally classified as __________ and structurally classified as ____________.

Synarthrotic, fibrous

In general, which of the following joints likely has the LEAST movement? - Saddle - Symphysis - Synovial - Synchondroses

Synchondroses. Right! Of these options, synchondrosis is always synarthrotic. IN general, synovial joints are more mobile. Saddle is a type of synovial. Symphysis joints are usually amphiarthrotic.

Without ____, bones become ____. - collagen; better able to withstand torsional forces - collagen; too brittle - mineral; better able to withstand tension - mineral; too brittle

Collagen, too brittle. Right! Collagen provides a framework for mineral deposition (calcification). Without collagen, the mineral is poorly aligned and bones become brittle. Just like we showed in class. Mineral is important to bones because it provide compressive strength, as long as collagen is able to keep it glued together. Without its glue, bones are a pile of salt. Collagen also gives bone tensile strength - when they are pulled, the collagen resists the pull, just like rope. Collagen also gives bone torsional strength - resisting twisting. If mineral is removed, it does not help the tensile or torsional strength of the bone.

The joint between mandibular condyle and mandibular fossa is functionally classified as __________ and structurally classified as _____________.

Diarthrotic, synovial

The liver is a glandular organ of the digestive tract. What is its most likely embryological origin? - ectoderm - mesoderm - endoderm

Endoderm. Right! The endoderm gives rise to the epithelium of the digestive tract, including the glands that support it (pancreas, liver, gall bladder). Glands are made of epithelial tissue. The mesoderm gives rise to many things, including muscles and bones, but not the liver. The ectoderm gives rise to the nervous system and skin.

Which of the following joints make the most appropriate pair?1. Joint between sternum and clavicle2. Joint between adjacent vertebral bodies3. Joint between superior and inferior articular processes of vertebrae4. Joint between two pubes5. Joint between temporal bone and occipital bone - 2 & 5 - 4 & 3 - 1 & 3 - 5 & 4

1 & 3. Right. 1. Joint between sternum and clavicle - diarthrosis planar (some call saddle) (synovial) 2. Joint between adjacent vertebral bodies - amphiarthorsis symphysis (cartilaginous)3. Joint between superior and inferior articular processes of vertebrae - diarthrosis planar (synovial)4. Joint between two pubes - amphiarthorsis symphysis (cartilaginous) 5. Joint between temporal bone and occipital bone - synarthrosis suture (fibrous) By structural class, 1 & 3 are a good pair - though it would have been nice if 2 & 4 was an option!

In this picture, how many complete sarcomeres are shown in the bottom panel (panel 4)? - 1 - 4 - 2 - 3

3. Correct! A sarcomere is a structural, microscopic unit of muscle that extends from one Z disc to another. It includes all the thick and thin filaments between the two Z discs. In the image, the bottom panel shows 4 Z-discs with 3 complete sarcomeres.

Whole skeletal muscles are organs. Therefore they contain (select all that apply): - Connective tissue - Neural tissue - Muscle tissue - Epithelial tissue - All of the above

All of the above. Right! Organs contain all tissue types. In whole skeletal muscles (like the biceps brachii), the muscle tissue is present as skeletal muscle tissue. That muscle tissue is in close contact with nerves (neural tissue) and blood vessels (which contain an inner lining of epithelial tissue). Whole muscles also contain many integrated layers of connective tissue (endomysium, perimysium & epimysium) connected to tendons (dense regular connective tissues).

What is a myofibril? - an organelle - a muscle cell - a muscle organ

An organelle. Right! Myofibrils are found inside muscle cells - they are an organelle. Specifically, they are composed of myofilaments - cytoskeletal proteins called actin and myosin.

As we age, the sacroiliac joint changes from being planar to being a syndesmosis. Which of the following would be consistent with this? - As we age, the joint has an increased synovial fluid production - As we age, the joint has an increased risk of dislocation - As we age, the joint has a decrease in stability - As we age, the joint has a decrease in mobility

As we age, the joint has a decrease in mobility. Yes. This joint is changing from a more mobile (synovial) to a less mobile (syndesmosis, a type of fibrous joint). Though the SI joint does not move much, this is describing a decrease in the number of elements associated with mobility. As mobility of a joint decreases, typically we would associate this with an increase in stability. The more stable a joint, the less mobile it is.

Which of the following would be a symptom of severe lack of vitamin D in children aged 4-6? - Being very tall - Bowed lower limbs - High blood calcium - Narrow medullary cavities

Bowed lower limbs. Right! Vitamin D is needed for absorption of calcium from the gut. People who do not have enough calcium (either by diet or lack of viitamin D) will have malformed bones. In particular, children will develop bowed legs because although they don't have calcium, they have collagen that makes their bones flexible, but not as supportive. Lack of vitamin D should not increase height, it might perhaps lower it due to reduced bone formation. Narrow medullary cavities result from excessive bone deposition at the endosteum. Again, without calcium this is hard to imagine. Without vitamin D, they cannot have high enough blood calcium - high blood calcium is almost always linked to excessive PTH.

These are sections through a sarcomere. Which letters would be taken from the A (dArk) band? - A, B, C, D & E - B, C & D - C, D & E - A & B

C, D & E. Correct! The A band is the region of the sarcomere that contains all of the myosin. A bands do not change length because the myosin does not fold during activation, it only sides past the thin filaments. Notice that all the sections that contain myosin are within the A band.

While riding her horse, Maria falls and completely tears all the ligaments of her glenohumeral joint. Which of the following treatments would help her recover and prevent future dislocations of this joint? - A surgery that removes her glenoid labrum - Exercises that strengthen her rotator cuff muscles - A surgery that fuses her acromioclavicular joint - Exercises that strengthen her brachialis

Exercises that strengthen her rotator cuff muscles. Right! The rotator cuff is a group of muscles that crosses the shoulder (glenohumeral joint) and provide stability to this joint. The labrum serves a similar role, though it is made of fibrocartilage. Removing the labrum would make this situation worse. The brachialis does not cross the shoulder. Fusing her AC joint (Acromioclavicular) would decrease range of motion of the upper limb.

During formation of the mandible, the first osteoblasts to appear were delivered by blood vessels. - True - False

False. Right. The mandible is formed by intramembranous bone formation. During intramembranous bone formation osteoblasts differentiate from mesenchyme cells before the arrival of blood vessels. This is in contrast to endochondral bone formation that requires blood vessels for successful action of osteoblasts.

Bone mass (or bone density) is homeostatically regulated. - True - False

False. This is false. Although blood calcium is homeostatically regulated (via the parathyroid and thyroid glands the subsequent release of PTH or calcitonin), bone mass is not. In order to regulate blood calcium, these hormones will take bone mass or add bone mass to balance the blood. When the blood is balanced in terms of blood Ca2+, bone will be influenced by other factors (growth hormone, estrogen/testosterone, exercise, diet etc). But nothing is monitoring bone mass (or bone density) and then maintaining it within a narrow range - this is why we need to monitor it consciously as we age (through bone density tests or imaging). We know that bone mass may be in peril when we break a limb or have high metabolic demand for calcium (think about a lactating female), but do not use a receptor to monitor it, a control center to interpret the information and an effector to correct it. Therefore, bone mass (bone density) is not homeostatically regulated.

True or False. This movement is rotation.

False. The movement shown is circumduction.

You find a tissue that has the following characteristics:avascularcells contain nuclei, rough ER, golgi apparatuses and mitochondriacells are widely spaced from one anotherWhere did this sample likely come from? - Osteon - Brain - Intervertebral disc - Mammary gland

Intervertebral disc. Right! The description of this tissue is avascular, cells contain nuclei, rough ER, golgi apparatuses and mitochondria the cells are widely spaced from one another. Of the four primary tissue types, epithelia and some connective tissues are avascular (cartilages). Neural tissue (the brain) and osteons (bones) are highly vascular, so these two answers are out. The described tissue has cells that make proteins for export (rough ER, golgi etc), so a mammary gland may be possible (breast milk contains protein), but so is an intervertebral disc. The intervertebral discs are made of fibrocartilage and they have extracellular protein fibers that are made by chondrocytes. The defining character here is the cells that are widely spaced from one another. In glands, the tissue cells are attached to one another and there is no extracellular material. In connective tissues, the cells are widely spaced from one another by ground substance, as described here. The best answer is the fibrocartilaginous intervertebral disc.

The liver is a glandular organ that functions to secrete many substances to the blood or digestive tract, detoxify chemicals and synthesize molecules utilized by all the cells of the body. What do you think is its likely histologic composition? - It is mostly neural tissue - It is mostly epithelial tissue - It is mostly cardiac muscle - It is mostly connective tissue

It's mostly epithelial tissue. Right! The liver is the largest gland in the body and is mostly specialized epithelial cells. It is definitely not neural tissue - only the brain, spinal cord and nerves are neural tissue. It is definitely not cardiac muscle tissue - cardiac muscle tissue is specialized for movement and is only found in the heart. You might suspect that the liver is connective tissue. However, you may remember that glands are epithelial tissue. The more organelles you can pack into a cell, the more that cell, and therefore that gland can do. Liver cells are large and well supplied with organelles to perform the liver's many functions (lots of rough and smooth ER and golgi apparatuses).

What level of organization is this image? - whole muscle - muscle fascicle - muscle cell

Muscle Cell. Right! This is a muscle cell. You might be able to tell by the mitochondria. Fascicles are bundles of muscle cells Whole muscles are bundles of fascicles

Does a single sarcomere contain a complete, continuous I band? - Sometimes - No, never - Yes, always

No, never. No, it does not. An I-band is the part of the myofibril that does not contain the myosin (the A-band). An I-band contains thin filaments joined by a Z-disc. Within a given sarcomere, 1/2 of an I-band is on one side of the the A-band, and another 1/2 of an I-band is on the other side of the A-band. However, these halves are not part of the same I-band. To have a complete, continuous I-band, you need to have two sarcomeres in series with the Z-disc at the middle of an I-band.

In skeletal muscle, the sarcoplasmic reticulum stores calcium. What organelle is the sarcoplasmic reticulum? - smooth ER - mitochondria - ribosome - golgi apparatus

Smooth ER. Right! In muscle, "sarco-" is a common prefix (we also use "myo-"). The sarcoplasmic reticulum (SR) is the smooth endoplasmic reticulum of muscle cells. In muscle, it stores calcium in very high concentrations. The calcium in the SR can be released into the cytosol of the cell when muscle contractions need to happen. While calcium is being stored, although it is inside the cell, it is not freely able to interact and cause contraction of muscle.

The below graphs show schematic illustrations of the effect of physical activity on bone mass throughout life for both male and female humans. For each graph, the red curve represents a continuous exercise effect (meaning, from the appearance of the red line, this is when exercise was introduced into their life and regular exercise remained). The yellow curve represents a sedentary person engaging in normal activities (such as walking, but not regular continuous exercise). Note for each group that exercise is introduced at different points in life (ages). Using this model, What can be said about bone mass? - Being continuously physically active has a bigger impact on bone mass than sex related differences. - Age at time of continuous physical exercise implementation does not affect end of life bone mass. - The greater peak bone mass, the greater end of life bone mass. - In older adult populations, the effects of continuous physical exercise are greater in males than in females.

The greater peak bone mass, the greater end of life bone mass. Correct! If you compare peak bone mass in all groups, the higher peak bone mass, the higher end of life bone mass (as a general trend). For individuals that introduce physical exercise at earlier points in life, the higher their end of life bone mass. In the oldest populations, exercise increased bone mass, but to a similar (or same) degree. Although physical exercise increases bone mass in all groups, the effects of exercise in females does not cause their bone mass to exceed that of males.

Which of the following happens during formation of the ulna? - Osteoid deposition occurs before the appearance of blood vessels - Cartilage cells are converted into osteoblasts - The epiphyses ossify before the diaphysis - The outer periosteal bone forms before the inner spongy bone

The outer periosteal bone forms before the inner spongy bone. Right! The ulna (like all long bones) forms via endochondral bone formation. During endochondral bone formation hyaline cartilage must die and be removed before osteoblasts can produce new bone on the remains of the cartilage. This bone deposition occurs at the outer edges of the structure to create a bony collar around the diaphysis. The osteoblasts depositing this bone must arrive via the invading blood vessel because cartilage cells cannot transform into bone cells. So, blood must precede bone in the case of endochondral bone formation. When long bones form, the diaphysis is the first site of bone formation. At birth, the diaphysis is usually bone but the epiphyses are still cartilage. The epiphyses ossify (creating secondary ossification sites) at different ages throughout childhood. The skeleton can be dated by the pattern of secondary ossification sites. See here for an authoratative listing of the ages at which the these centers

Which are synovial joints? - The sacroiliac and the joint between the articular processes of adjacent vertebrae - All of the listed joints are synovial - The joint between the spinous processes of adjacent vertebrae and the joint between the flat bones of the skull - The joint between the pubes and the joint between the bodies of adjacent vertebrae

The sacroiliac and the joint between the articular processes of adjacent vertebrae. Right! The sacroiliac and the joint between the arches of adjacent vertebrae (joint at the superior and inferior articular processes) are synovial (both are planar). Although we do not typically think these joints as mobile as perhaps the shoulder, they are lined with synovial membranes and thus are synovial joints. The joint between adjacent vertebral bodies or the joint between the two pubes are cartilaginous symphysis joints. The joint between the spinous processes of adjacent vertebrae and flat bones of the skull are both fibrous joints (spinous processes joint = syndesmosis, joint between flat bones = suture).

What is this? - Myofibril - Sarcomere - Sarcolemma - Thin filament - Thick filament

Thin filament. Right! The thin filament is a part of the myofibril. Thin filaments are made mostly of the myofilament actin. They are also made of other cytoskeletal proteins troponin, tropomyosin and nebulin. The thick filament is made mostly of myosin, but also contains titin. Myofilaments are organized into sarcomeres. Sarcomeres are in series running the length and breadth of myofibril. Since this image does not contain a thick filament, it cannot be a sarcomere or a myofibril, only part of them, the thin filament.

Using figure 1, when are the potassium leak channels open?

At all times. Right! The potassium leak channels are always open. There is never a time when they are closed (reliably).

Using figure 1, when do the sodium voltage gated channels first open and allow ion movement across the cell membrane?

At the beginning of C. Right! The beginning of C marks the beginning of the depolarization phase of the action potential. The depolarization is due to passage of Na+ into the cell through open voltage gated Na+ channels.

Cells of the thyroid and parathyroid glands are sensitive to blood calcium levels. Which of the following is the most likely mechanism by which blood calcium levels are detected?

Calcium binds to a cell membrane receptor which activates a second messenger system Right! Calcium is charged - it cannot diffuse simply through the membrane (fat soluble do this); it is more concentrated outside cells due to all cells having a calcium pump on them, constantly keeping extracellular calcium levels high; even if calcium were to enter cells, it would depolarize them, not hyperpolarize them. It is true that calcium binding on these cells activates second messenger systems, leading to cellular response.

Starting with the resting state, what happened to the membrane permeability for the shown ion in these panels?

It increased. Right! The membrane permeability to this ion increased when the gated channel opened.

What type of epithelium is shown here?

stratified squamous epithelium Right! This is a multi-layered epithelium (making it stratified) with the top cells being flat and thin (squamous). Although the bottom layer cells are cuboidal, by convention we classify stratified epithelia by naming the top cell. This is the epidermis.

Resting Membrane Potential (RMP) is the potential difference that exists across a membrane of an unstimulated cell (i.e. cell at rest). What is the RMP for a typical neuron shown above? (This is model 1 from the activity sheet in class #3, Thursday week 1).

-70 mV Yes. Notice in the middle of the graph, the flat line is labeled "resting membrane potential." This is at -70 mV.

What directly causes a voltage gated channel to open?

A change in the transmembrane potential due to some factor Correct! Voltage gated channels are membrane proteins that open when the surrounding membrane transmembrane potential (electricity) changes. Not just any change in the membrane potential will cause the voltage gated channel to open, but only when the membrane reaches a particular transmembrane potential. This membrane potential value that causes the voltage gated channel to open is called threshold. Chemically gated channels open when a chemical binds to a receptor on the channel. Mechanically gated channels open when the surrounding membrane (or channel) is physically changed (deformed). ATP can act as a neurotransmitter causing certain chemically gated channels to open.

Using figure 1, when does the action potential begin?

At the start of C. Yes. The AP begins at the start of time C. B shows a graded depolarization, not the start of the AP.

Given the image above, will increased Na+ diffusion cause the membrane to depolarize or hyperpolarize and why? (This is model 2 from the activity sheet in class #3, Thursday week 1).

Depolarize because Na+ will enter the cell Yes. Sodium is more concentrated outside cells due to the Sodium-Potassium Pump. When sodium is permitted to cross the membrane through an open Na+ channel, it enters the cell. The movement of + charges across the cell membrane creates a current that is less negative/more positive than the resting membrane potential. This is known as a depolarization. Hyperpolarizations are when the membrane potential becomes more negative than resting levels. This can be due to the influx of anions (- ions) or efflux of cations (+ ions). Since Na+ would passive diffuse inward (from high outside to low inside), it cannot create a hyperpolarization in this case.

For connective tissue compared to muscle tissue, do cells or extracellular matrix (ECM) make up more of the total tissue volume? - ECM - Cells

ECM. Yes, if you look at the pictures of the connective tissues shown above, most of the tissue volume is made of extracellular matrix (ECM). This matrix is made of fibers (proteins called collagen, reticular fibers, or elastic fibers) and ground substance (the stuff between the fibers that can be liquid or solid).

The most abundant type of cell in your epidermis is: - Keratinocytes - Langerhans cells - Melanocytes - Merkel cells

Keratinocytes. Right! More than 90% of cells in the epidermis are the keratinocytes that are cells packed full of keratin. The other cells are low in number but each have important jobs (melanin production for melanocytes, sensation for Merkel's cells and immune function for Langerhans cells).

Which trace(s) of the transmembrane potential shows additional action potentials occurring during the absolute refractory period?

None. Correct! During the absolute refractory period it is impossible to generate another action potential due to the state of the voltage gated sodium channels. So, none of these traces show an AP during the absolute refractory period.

True or False? Accessory structures are called "epidermal structures" because even though they reside in the dermis, they are made of, and by, epidermal cells.

True. Right! During fetal development, the same cells that give rise to the epidermis (ectoderm cells) give rise to the cells that produce the hair, glands and nails. Hair and nails are really just stacks of epithelial cells that form in the same way the stratum corneum forms. Mitosis of stem cells in a basal layer (hair matrix for hair, nail matrix for nails) occurs and the older cells get pushed to the apical surface. And if you look at the origins of the hair matrix and nail matrix, you will find that the cells that are presently there used to be cells of the stratum basale (germinativum) in the embryo/fetus. During development these cells grew downward and became anchored in the dermis.

True or false? Keratin is an intracellular protein.

True. Right. Keratin is found inside cells of the epidermis. It is an intracellular protein. Even though you may think of hair and nails as being made of keratin, this is true, because hair and nails are made of stacks of cells filled with keratin.

Does a resting neuron consume ATP? (Neurons are resting when they are neither sending nor receiving a signal.)

Yes. Correct! Resting neurons are spending ATP to move ions across their cell membranes (Na+/K+ ion pump). Even at rest, these pumps are active - no rest for the wicked!!

What type of membrane protein is shown here? (The bottom yellow portion of each panel represents the cytosol)

chemically (ligand) gated sodium channel Correct! This channel responds to the presence of Ach (acetylcholine) - a neurotransmitter. When Ach binds, the channel opens, allowing an ion to flow. The ion flows into the cell in the image - this means that the ion is more concentrated outside of the cell than in. Sodium is more concentrated outside of cells than in, and potassium is more concentrated inside cells than out. If this were a potassium channel, the potassium would flow out. Leak channels are not gated and do not respond to chemicals like Ach. Voltage gated channels respond to changes in membrane potential not Ach.

Depolarization and hyperpolarization are two types of alterations in resting membrane potentials. Using the previous image, match the following membrane values to the shown terms: resting, depolarized or hyperpolarized.

0 mV --> depolarization -70 mV --> resting membrane potential -100 mV --> hyper-polarization -71 mV --> hyper-polarization 30 mV --> depolarization Resting membrane potential as listed above is -70 mV (in truth, this is different for different cells and is really an average of values recorded over time). Any membrane potential away from resting that is greater than -70 mV (-69 mV and upward) is considered a depolarization (unless the membrane is return back towards rest from being depolarized). Any membrane potential below -70 mV (-71 mV and more negative) is considered a hyper-polarization.

Using this figure, which cells (numbers) are affected by the red circles (hormones)?

3, 4, & 5 Right! Hormones circulate throughout the blood and bind to receptors located either on the cell membrane surface or within cells. Only cells with specific receptors can respond to the specific hormones that fit those receptors. Here, the red circles can fit into the cell membrane receptors of cells 3, 4 & 5 because those cells have the half circle receptor. The red hormone is a water soluble hormone - we can tell this because its receptor is on the cell surface. Fat soluble hormones can diffuse through the cell membrane, water soluble cannot. This is why water soluble hormones must bind to the cell membrane surface receptor and then active second messengers inside the target cell.

Which of the above traces would be most consistent with the longest opening of a K+ chemically gated channel?

3. Right! Opening a K+ channel will allow K+ to leave a cell, causing a hyperpolarization. The longest duration of opening would produce the largest hyperpolarization - #3. 1 is smaller than 3, 6 is a depolarization. 7 is an action potential and even though the membrane hyperpolarizes at the end of the action potential, this is not due to chemically gated K+ channels. It is due to K+ voltage gated channels.

Which of the above traces best matches figure A in this quiz (membrane protein image)?

4, 5 or 6 (but not 7) Right! 1, 2, & 3 are graded hyperpolarizations and would be observed if K+ or Cl- were crossing the membrane through a chemically gated channel. In the other image, a cation is shown entering the cell through a chemically gated channel. This ion is likely sodium because it is flowing into the cell down a gradient and is monovalent. Depolarizations are created by sodium flow through a chemically gated channel (4, 5 or 6). 7 is an action potential - it occurs when voltage gated channels open, not chemically gated channels.

Arrange the following structures in the correct order starting with the simplest level of organization and ending with the most complex. 1. Cell membrane 2. Epithelial cell 3. Human 4. Digestive system 5. Phospholipid 6. Small intestine

5, 1, 2, 6, 4, 3 Right! Ordering questions are often on my exams. When approaching an ordering question, you can either try to order the options yourself and then check to see if your order matches an answer, or you can look through the options. If you look here, each option begins with either 3 or 5. Regardless of the answer you choose, you should always look at the given orders and eliminate the really wrong ones. The most common error people make with ordering questions is reading the question incorrectly. If you selected an option that began with the whole human (3) as the first number, it is likely that you were organizing the numbers from most complex structural organization to least complex structural organization. Another place where folks go wrong here is to get thrown off by the fact that the levels of organization are not exactly as displayed in class. Here you have to look at each structure and identify it as a molecule, or a part of a cell, a whole cell, an organ, or an organ system. Then you have to put them into an order that is more familiar to you.

To create a graded hyperpolarization in the postsynaptic cell, the following events would need to occur in which of the following orders (you may or may not need to use all numbers below). 1. Voltage gated calcium channels open. 2. Neurotransmitter binds to chemically gated channels. 3. Synaptic vesicles migrate to cell membrane. 4. Neurotransmitter released into synaptic cleft. 5. Action potential arrives at terminal end (knob). 6. Sodium rushes into the postsynaptic cell. 7. Potassium rushes out of the postsynaptic cell.

5, 1, 3, 4, 2, 7 Correct

Big graph. Above is trace of the transmembrane potential of a neuron taken at single location in the neuron. Each number refers to durations between the successive dashed lines. The graded potentials are due to one type of ion movement.Using the big graph above, which trace(s) directly reflect/s movement of chloride ions through open chemically gated channels (adult cell)?

5. Right! Only #5 shows a graded hyperpolarization. If you read the caption for the figure, it states that each graded potential occurs only due to one type of ion. When Cl- channels open, Cl- rushes into the cell. When the channels close, the membrane potential returns to resting levels.

Which cell is not affected by any of these hormones?

6. Right! This is because cell 6 does not have any receptors for these hormones. Unlike neurotransmitter in the nervous system in which a neuron releases the NT right onto the target cell (postsynaptic cell), hormones circulate throughout the entire body. In theory, anywhere the blood goes, all hormones go. This means that cells are constantly bathed in all the body's hormones, but only cells with receptors for a hormone will respond to that hormone.

Using figure 1, which traces are most likely caused by the opening of voltage gated K+ channels?

8 & 9. Right! 8 & 9 indicate the membrane potential during the repolarization and hyperpolarization phases of the action potential. These phases are due to opening of voltage gate K+ channels. The other trace that are below resting level are most likely due to opening of chemically gated K+ channels (4) or recovery from the action potential when the membrane pumps are active (10). 2 & 6 are graded depolarizations and are not due to opening of K+ channels. If K+ channels were to open, K+ would leave the cell creating a hyperpolarization. Depolarizations (such as 2 & 6) would be due to influx of Na+ or Ca++.

Using figure 1, what type of stimulus would generate another action potential during E & F?

A large suprathreshold depolarizing graded potential. Correct! This is the relative refractory period. The voltage gated sodium channels are reset and available, but the exflux of potassium must be overcome by a larger than normal depolarization for threshold to be achieved.

In certain neurological disorders, the neurons controlling muscles continuously activate skeletal muscles causing rigidity. Which of the following medications would be most effective at treating these disorders?

A medication that extends the absolute refractory period in these neurons Right! We want to decrease NT release from neurons. Since NT is released each time action potentials travel down the neuron, if we increase the duration of the absolute refractory period, fewer APs per minute will be possible on the neuron. With fewer APs, there will be less NT release. Increasing vesicle exocytosis will increase NT in the cleft and make the problem worse. Inhibiting re-uptake means that neurons do not remove NT from the synaptic cleft. Increasing Ca++ entry into the presynaptic neuron will cause more vesicle release, making the problem worse.

What is meant by the term "chemically gated sodium channel"?

A membrane channel that opens when some chemical binds to it, allowing sodium to cross the cell membrane Correct! Neurotransmitters are chemicals released from neurons that bind to chemically gated channels. If the gated channel is specific for sodium, once the neurotransmitter binds, the gate opens and sodium flows down its concentration gradient into the cell. For more resources on this concept, please refer to your text book, the DVD or the animations on BB.

What directly causes a chemically gated channel to open?

A neurotransmitter binding on the chemically gated channel Correct! Chemically gated channels are membrane proteins that open when a chemical binds to a receptor on the channel. The chemical that causes them to open, if released from a neuron, is called a neurotransmitter. Voltage gated channels are membrane proteins that open when the surrounding membrane transmembrane potential (electricity) changes. Not just any change in the membrane potential will cause the voltage gated channel to open, but only when the membrane reaches a particular transmembrane potential. This membrane potential value that causes the voltage gated channel to open is called threshold. Mechanically gated channels open when the surrounding membrane (or channel) is physically changed (deformed).Regardless of the type of gated channel, channels are specific for the ions they allow to cross the cell membrane and only allow ions to cross the cell membrane using their diffusion gradients. Meaning, they only allow sodium to enter the cell because there is so much sodium outside of cells compared to inside of cells. The reverse is true for potassium.

Which of the following will cause a graded hyperpolarization on a postsynaptic neuron?

A neurotransmitter binding to a chemically gated potassium channel Correct! At a synapse, the presynaptic cell communicates with the postsynaptic cell. At a chemical synapse, the presynaptic cell releases a chemical (neurotransmitter) that binds to chemically gated channels on the membrane of the postsynaptic cell. When a chemically gated channel opens, specific ions may move down their concentration gradients (from high to low). The concentration gradient for potassium is to move out of the cell. When potassium moves out of the cell, it removes positive ions from the cellular interior, thus leaving the cell more negative. A hyperpolarization is a change in the transmembrane potential from resting values to something more negative (perhaps -70 mV to -90 mV). Neurotransmitters do not bind to voltage gated channels. Opening a sodium channel would lead to a graded depolarization. Because sodium would move down its concentration gradient into the cell, this would make the interior less negative (move closer to 0 or positive values; perhaps from -70mV to -20 mV).

What is the effect of increased blood flow to the dermis? - All of the above. - It increases heat loss to a colder external environment. - It increases nutrient delivery to the cells of the epidermis. - It causes a change in light skin color in the area of increased blood flow.

All of the above. Right! Increasing blood flow to the dermis results in a reddening of the skin due to an increase in blood volume in the dermis. The more blood you deliver to the dermis, the more opportunity you have to lose heat across the skin to the outside world. Increased blood flow to the dermis also results in increased nutrient delivery to the tissues in that area. Because the epidermis receives all its nutrients by diffusion from the dermis, when blood flow to the dermis increases, so does delivery to the epidermis. When you have injuries to an area of the body, blood flow increases so that the cells responsible for healing the injury can have enough raw materials to do their job. This causes redness and swelling of the area as well as heat due to the increased blood volume.

Which of the following statements best explains the image above?

All stimuli opened calcium gated channels Right! These are each depolarizations called graded potentials (depolarizing graded potentials). Depolarizations are caused by influx of cations into the cell (here, Ca+) or efflux of anions. When Cl- channels open, Cl- rushes into cells - it always is associated with sodium, so if sodium is more concentrated outside of cell, so is chloride. Hyperpolarizations occur when potassium (K+) channels open too because the K+ leaves the cell down its concentration gradient, making the cell interior relatively less positive (negative). When allowed to cross the membrane, Cl- will enter a cell, causing a hyperpolarization, not a depolarization. Though stimulus 3 is largest, it is not an action potential. Action potentials are characterized by a different shape that will discuss next week.

The compressible fibrocartilaginous joint between spinal vertebrae is functionally classified as ________ and structurally classified as _____________.

Amphiarthrotic, cartilaginous

Using figure 1, when do the sodium voltage gated channels first become inactivated?

At the end of C. Right! The sodium channel becomes inactive at the peak of the action potential.

The sarcoplasmic reticulum of skeletal muscle cells has a very high calcium concentration. Which of the following would explain why the concentration of calcium is so high in the sarcoplasmic reticulum during rest? - Because ATP dependent pumps actively move it there from the sarcoplasm - Because the t-tubule passed calcium ions there during the action potential - Because the neuron released calcium there during the action potential - Because calcium ions diffused in there during rest.

Because ATP dependent pumps actively move it there from the sarcoplasm. Right! The sarcoplasmic reticulum has pumps that use ATP to actively move calcium into the interior of the sarcoplasmic reticulum (SR). The concentration can be very high in the SR because these pumps use energy to move ions against the concentration gradient - meaning that they move the ions from a place that is less concentrated (the sarcoplasm) to a place that is more concentrated (the SR). During an action potential, the calcium release channels on the SR open and the calcium can move down its gradient from high in the SR to low in the sarcoplasm. The greater this gradient, the faster the calcium will flow out and the more it can influence contraction once released.

After a fracture, what is the correct sequence of repair for indirect bone healing? (Take a look at your notes from lecture 10) - Cartilage patch, blood clot, bony patch, bone remodel - Blood clot, bony patch, cartilage patch, bone remodel - Blood clot, bony patch, bone remodel, cartilage patch - Blood clot, cartilage patch, bony patch, bone remodel

Blood clot, cartilage patch, bony patch, bone remodel Right! Blood is always the first to arrive at an injury. After the fracture hematoma (blood clot) forms, a fibrocartilaginous callus (patch) forms. The cartilage is then replaced by a temporary bony callus. The bony callus is finally remodeled into mature bone.

Which of the following happens during intramembranous bone formation? - Bone deposition occurs before blood vessel invasion - The outer periosteal bone forms before the inner spongy bone - Blood vessels deliver osteoblasts which then produce the first osteoid - Disorders of chondrocyte mitosis are very damaging to the bone formation

Bone deposition occurs before blood vessel invasion. Right! During intramembranous bone formation mesenchymal cells differentiate to become osteoblasts which then produce new bone. The mesenchymal cells are already present in the tissue, blood vessels are not required. In fact, bone formation precedes blood vessels. As the new bone forms, it traps the blood vessels within spongy bone trabeculae. The outer compact bone from the periosteum is the last bone to form. This type of bone formation does not involve cartilage at all, so mitotic problems with cartilage cells should not impact intramembranous bone formation.

What will happen to bone mineral density if osteoblast activity is unchanged but osteoclast activity decreases? - Bone mineral density will increase relative to some baseline state - Bone mineral density will not change relative to some baseline state - Bone mineral density will decrease relative to some baseline state

Bone mineral density will increase relative to some baseline state. Right! When osteoblast and osteoclast activity is matched, bones will neither grow weaker or stronger. When osteoblasts are more active than osteoclasts, bone mass will increase. When osteoclasts are more active than osteoblasts, bone will become weaker. Bone mineral density is an indicator of overall bone mass. So, if osteoblasts and osteoclasts are at some state and osteoclasts decrease activity, the bone mineral density will relatively increase. This is the mechanism of action for bisphosphonate medications.

Which statement correctly describes both the epidermis AND dermis? - Both are composed of connective tissue. - Both contain adipocytes. - Both are superficial to the hypodermis. - Both are made mostly of keratinocytes. - Both are highly vascular.

Both are superficial to the hypodermis Right. The hypodermis is deep to the dermis, which is deep to the epidermis. The epidermis is avascular because it is an epithelium, though the dermis is highly vascular. Adipocytes are connective tissue cells and are not found in the epidermis. Keratinocytes are epithelial cells that make up the epidermis. Some keratinocytes will be found in the dermis as the accessory structure roots (like in hair follicles), but these are not the majority of the tissue volume and are not the most abundant cells located there.

Where must threshold be reached to send a signal all the way down the length of the neuron?

Both at the trigger zone and at each node of Ranvier Right! Signal conduction down an axon requires the action potential to be generated (or regenerated) at each exposed portion of the axon. To generate an AP at each section of the neuron, you must bring that section to threshold so that voltage gated sodium and potassium channels can open. Typically, the first place where an AP is generated is at the trigger zone (initial segment). Then, the AP must be recreated at each section of the neuron to transmit the signal to the end of the neuron.

Looking at these graphs, what is different about the calcitonin graph compared to the others (calcitonin is the lower left graph)? - Calcitonin graph also shows a placebo, the others do not. - Calcitonin has a shorter time frame than the others. - Calcitonin has an effect much larger than all others. - Calcitonin has a smaller bone mineral density change compared to the others.

Calcitonin has a smaller bone mineral density change compared to the others. Right! The calcitonin graph has a vertical axis that ends at 2%. All vertical axes are percentage change from baseline for bone mineral density and all but calcitonin goes up to 6% change. All time frames are in months, but calcitonin is in years - much longer than the others. All graphs have the treatment (calcitonin, growth hormone, estrogen or bisphosphonates) against a placebo. The calcitonin effect is much less than the others. It does not change bone mineral density as much and takes longer to achieve its effects.

Which of the following is the most likely mechanism by which blood calcium levels are detected in the thyroid and parathyroid? - Calcium is pumped into the cell, down its concentration gradient - Calcium binds to a cell membrane receptor which activates a second messenger system - Calcium entry hyperpolarizes the thyroid and parathyroid cells, creating a signal - Calcium enters the cell by simple diffusion and binds to an intracellular receptor

Calcium binds to a cell membrane receptor which activates a second messenger system Right! Ca2+ is charged and must enter a cell via pump or channel (not simple diffusion). If it does not do that (none of the options above offered that), then it must bind at the surface and activate a second messenger. It is does enter a cell, it depolarizes it. It is more concentrated outside of cells, so a pump will pump it out, not in.

In the picture of the epidermis in this quiz, what are those lines between the keratinocytes? - Collagen fibers - Keratin fibers - Desmosomes

Desmosomes. Correct! Desmosomes are membrane proteins that extend from one cell to another. They provide mechanical strength to epidermis, linking cells together. These junctions are not so tight as to prevent material from sliding between the cells (tight junctions would prevent such a thing), but they do allow flexible connectivity. Gap junctions would be holes between adjacent cells and we see those in smooth muscle cells and cardiac muscles cells where ions can flow between the cells allowing action potentials to spread without neurotransmitter. Collagen is an extracellular protein fiber that is found in connective tissues, not epithelia. Keratin is an intracellular protein, not located on the external surface of the cell membrane.

To be activated, skeletal muscle fibers must receive neurotransmitter from neurons. What structure must neurons penetrate to activate the myofiber? - Sarcoplasmic reticulum - Endomysium - Myofibril - Sarcolemma

Endomysium. Right! Blood vessels (capillaries) and neurons must come very close to a muscle cell (myofiber) to control it (neuron) or supply it with nutrients (capillary). However, the neuron and capillary do not penetrate the cell membrane (sarcolemma). They stop beneath the endomysium but above the sarcolemma - the space between the neuron and the sarcolemma is the synaptic cleft. The sarcoplasmic reticulum and myofibril are organelles within the cell and therefore are too deep to be reached directly by the neuron and capillary.

How do nutrients reach osteocytes trapped between lamellae of osteons? - diffusing from the central canal to the cells via canaliculi - diffusing from the central canal through the mineralized matrix - actively pumped from central canal through gap junctions in the osteocytes - it does not; the cells are dead an do not need nutrients

Diffusing from the central canal to the cells via canaliculi. Right! As osteoblasts secrete their matrix, it mineralizes around them and they become trapped. Each lamella is a ring of osteoid secreted by osteocytes that eventually mineralizes and traps the osteocytes within pockets (lacunae). However, cytoplasmic processes of the osteocytes radiate out away from the lacunae and inhibit mineralization from filling in all the cracks between lamellae. Inside these cracks (called canaliculi), the osteocytes extend themselves and form gap junctions with their neighboring cells. The cells closest to the central canal receive the nutrients that diffuse out of the blood in the central canal and then allow them to diffuse outward through the connected cells within the canaliculi to the further and further osteocytes. These canaliculi are also useful for transmitting physical stress to through the bone, allowing bone to sense physical forces applied to bone and respond accordingly.

How does the epidermis receive its nutrients? - Diffusion from capillaries in the dermis. - Diffusion from capillaries in the stratum germinativum (basale). - Blood vessels in all layers of the epidermis.

Diffusion from capillaries in the dermis. Right! The dermis is immediately deep to the stratum basale (germinativum). The capillaries in the upper region (papillary layer) deliver nutrients to this area and diffusion from the papillary layer upward nourishes the epidermis. This is why as you move further toward the apical surface, cells die in the epidermis. They are moving further from the nutrient source and diffusion is limited by distance. The epidermis is an epithelial tissue and like all epithelial tissue, has no blood supply (avascular). This does not mean the cells are dead (not all cells, anyway), just that there are no capillaries scattered among the epidermal cells.

According to this image, what connective tissue layer surrounds whole muscle? - Epimysium - Perimysium - Endomysium

Epimysium. Right! Epimysium is a denser connective tissue that contains fibers (reticular & collagen fibers) and cells (fibroblasts) that surrounds whole muscles ("epi" means above, "mysium" means muscle - above the muscle). Surrounding individual cells/fibers is an endomsyium - "endo" means within. The endomysium is deep in the muscle, surrounding individual muscle cells, above the cell membrane. (Skeletal muscle cells are also called muscle fibers because they are long.) The endomysium is a looser connective tissue than the epimysium - it is an areolar connective tissue combined with reticular connective tissue. The endomysium is connected to muscle cell membrane through linking proteins and is also between all the muscle cells, linking them to each other. The perimysium surrounds bundles of muscle cells/fibers. These bundles are called fascicles and the connective tissue wrapper around them is in-between the fiber density of the endomysium and epimysium. All three types of connective tissues are continuous with each other and blend together with the tendon, that runs onto the bone.

What type of fluid is found in the transverse tubules (t-tubules)? - Extracellular fluid (ECF) - Intracellular fluid (sarcoplasm)

Extracellular Fluid (ECF) Right! The t-tubules are inward extensions of the sarcolemma. The sarcolemma is in contact with the ECF externally and the sarcoplasm internally. When the t-tubules extend down, they maintain this relationship.

True or False? All epithelial cells are dead because all epithelial tissues are avascular. - False - True

False. Correct! While it is true that epithelial tissues are avascular (meaning that they lack blood vessels), they are not all made of dead cells. The blood supply in the underlying connective tissue delivers oxygen and nutrients to the connective tissue, near the lowest level of the epithelial cells. These nutrients and oxygen diffuse into the connective tissue and then up to the epithelial cells. The closer the epithelial cells are to the bottom of the epithelial layer, the closer they are to the nutrients and the further the epithelial cells are from the bottom (closer to the top), the further they are from the nutrients. Your skin is made of stratified squamous epithelium and the cells at the top are indeed dead because they have migrated so far from the diffusing nutrients. The cells are the bottom however, are alive and constantly growing and dividing to replace the surface cells lost to the world.

If a physiological variable is regulated within a normal range, it is appropriately described as being "homeostatically regulated."

False. Homeostatic regulation requires 3 components: a sensor, an control center and an effector. Many variables in the body are regulated within ranges, but true homeostatic regulation requires all 3.

True or False? People with darker skin have more melanocytes than people with lighter skin.

False. This is false. Skin color reflects epidermal activity and dermal activity. All people (except those with albinism) have approximately the same number of melanocytes, but the level of melanin production differs. Darker skin results from increased melanocyte activity to produce more melanin which is then incorporated into the nearby keratinocytes. Once in keratinocytes the melanin accumulates around the surface of the nucleus exposed to the sun. When solar UV radiation enters the keratinocytes the melanin absorbs it and dissipates the energy as heat, preventing the cell's DNA from damage. The more melanin you produce, the darker your skin and the more you are protected from the damaging effects of the sun's UV radiation. This is why people develop tans when exposed to the sun. The dermis can influence skin color by the degree of blood flow within it. The more blood flow, the redder your skin becomes; the less blood flow, the paler your skin becomes. When blood is unable to carry oxygen, the blood becomes bluer in color (deep purple) and gives the skin a bluish tint (this condition is called cyanosis from the Greek "kyanos" which means blue).

True or False? Endochondral bone formation stops at birth. - True - False

False. Right! Endochondral bone formation forms most of the bones of your body. The process begins in the embryo when hyaline cartilage bones are replaced by osseous tissue. However, the process continues at the epiphyseal plate (growth plate) until adulthood. At the epiphyseal plate a thin line of hyaline cartilage remains and continues to grow through interstitial growth. As new cartilage grows, the epiphysis and diaphysis are pushed further away from each other. The older cartilage on the diaphyseal side of the growth plate is continuously degraded and replaced by bone. In this way the bone grows longer. At fully maturity (18-25 years of age), the hyaline cartilage is completely replaced by bone at the epiphyseal plate and the bone can no longer grow in length.

Muscle tissue is specialized for creating movement. Connective tissues are all derived from a common embryological tissue (mesenchyme which can derive from either ectoderm or mesoderm) and perform various functions including support, binding, storage, and transportation. In this image, the top panel shows the three types of muscle tissue, the bottom panel shows some of the many connective tissues. For Connective Tissue, are the cells relatively close to each other or relatively far from each other (when compared to muscle)? - Farther away than muscle cells - Closer together than muscle cells

Farther away than muscle cells. Yes, in connective tissues, the cells make up very little of the tissue volume. Most of the tissue volume is extracellular materials. Therefore, the cells are relatively far apart compared to muscle tissue. Muscle tissues are made of many densely packed cells (similar to epithelial tissues).

According to this image, what is wrapped by the perimysium? - whole muscle - fascicles - single muscle cells

Fascicles. Right! The perimysium surrounds bundles of muscle cells/fibers. These bundles are called fascicles and the connective tissue wrapper around them is in-between the fiber density of the endomysium and epimysium. Epimysium is a denser connective tissue that contains fibers (reticular & collagen fibers) and cells (fibroblasts) that surrounds whole muscles ("epi" means above, "mysium" means muscle - above the muscle). Surrounding individual cells/fibers is an endomsyium - "endo" means within. The endomysium is deep in the muscle, surrounding individual muscle cells, above the cell membrane. (Skeletal muscle cells are also called muscle fibers because they are long.) The endomysium is a looser connective tissue than the epimysium - it is an areolar connective tissue combined with reticular connective tissue. The endomysium is connected to muscle cell membrane through linking proteins and is also between all the muscle cells, linking them to each other. All three types of connective tissues are continuous with each other and blend together with the tendon, that runs onto the bone.

Which of the following explains why females at end of life have lower bone mass than males? (This image is Model 1 from the activity from Tuesday week 6) - The bone cells of men are more responsive to exercise - Males have higher dietary requirements for protein and calcium - Males secrete more parathyroid hormone than females - Females have lower peak bone mass than males

Females have lower peak bone mass than males. Right! Peak bone mass predicts end of life bone mass. Since bone mass declines with age after peak, the higher the peak, the higher the end of life mass. Men cells are just as responsive to exercise as females (same changes in bone mass graph associated with exercise in men and women). Males higher dietary calcium and protein would be consistent with their need to maintain a higher bone mass, but does not really answer the question - you would assume that males and females are both maintaining their bone mass, not that one group is intentionally negligent. If males secreted more PTH than females, that might mean that they reduce their bone mass more over time than females (unless the PTH level is consistent with their metabolic needs, but then so would the female level of PTH and again, would not explain a difference in end of life bone mass).

Which organ is best described as one in which most of the tissues have some cells, but there is more extracellular matrix than cells and that ECM is solid at maturity? - Heart - Liver - Brain - Femur

Femur. Correct! The four primary tissue types are epithelial, connective, muscle and neural. Connective tissues are characterized by their cell types and extracellular matrix. For the ECM, we use the terms ground substance and fibers. Of this list, bone (the femur, thigh bone) is the one with the most connective tissue. The brain is composed mostly of neural tissue, the heart is composed mostly of cardiac muscle and the liver is a gland (composed mostly of epithelial tissue).

In terms of functional properties, osteoid that fails to mineralize is likely most similar to: - endosteum - bone marrow - skeletal muscle - fibrocartilage

Fibrocartilage. Yes! Osteoid is unmineralized matrix of bone. Since the non-mineral part of the matrix is collagen, and fibrocartilage contains collagen, functionally speaking, of the ones listed here, osteoid would be most similar to fibrocartilage. Bone marrow does not contain collagen. Skeletal muscle does not contain collagen. The endosteum is a single layer thick of bone cells. Osteoid is unmineralized matrix of bone. Since the non-mineral part of the matrix is collagen, and fibrocartilage contains collagen, functionally speaking, of the ones listed here, osteoid would be most similar to fibrocartilage. Bone marrow does not contain collagen. Skeletal muscle does not contain collagen. The endosteum is a single layer thick of bone cells.

Collagen is an extracellular protein made by cells and released into the interstitial fluid. What organelles would most likely be abundant in the cells that make collagen?

Golgi Apparatus Right! Collagen is a protein that must leave the cell via exocytosis. Rough ER make the protein, the golgi repackage it and then send it to the cell membrane for exocytosis. Free ribosomes are important for production of proteins that remain in the cytoplasm. In biology there are always a few exceptions and indeed there are a few proteins that are made by the free ribosomes that end up in membranous organelles - these include some proteins of peroxisomes, mitochondrial proteins and a select group of small secretory proteins. The general rule of thumb is that proteins that are associated with membranes (vesicles or the cell membrane) are created by rough ER and cytosol proteins are created by free ribosomes. Smooth ER makes carbohydrates and fat.

Acetycholinesterase (AchE) is the enzyme that breaks down the neurotrasmitter acetylcholine (Ach). In skeletal muscle cells, Ach opens chemically gated sodium channels. Ach is necessary for activating skeletal muscles cells - once activated, skeletal muscle cells produce force. Using the graphs, which graph best depicts the effect of increasing acetylcholinesterase activity on skeletal muscle force production? - Graph A - Graph B - Graph C - Graph D

Graph A. Right! Horizontal axis would be increasing acetylcholinesterase activity, vertical axis would be skeletal muscle force production. Acetylcholinesterase (AchE) destroys Ach. Without Ach, the muscle cell cannot generate force. The more active the AchE (which resides in the synaptic cleft), the less Ach can stimulate muscle and muscle force declines. This is best shown as Graph A, a declining line.

Using the graphs, which graph best depicts the effect of age at time of regular exercise introduced (min=5 years, max = 80 years) on end of life bone mass? Assume otherwise equal factors (sex, hormone level, diet, etc). (Age at time of regular exercise introduced means that at age 5, this person started exercising regularly and continued to do so until they died.) - Graph A - Graph B - Graph C - Graph D

Graph A. We have already explored in graphs that if you have a higher peak bone mass, you will have a higher end of life bone mass. Assuming otherwise equal factors, when you introduce weight bearing activity, you get an increase in bone mass. The earlier you introduce exercise, the more of an impact it has on bone mass - children engaging in regular weight-bearing physical activity will have higher peak bone mass, and then higher end of life bone mass than people for whom exercise was introduced later in life. Although the actual graph is likely more like a plateau to start, it will decrease with age of activity onset.

Which graph best represents what happens to the size of the zone of overlap (relative from min to max) as H-zone gets bigger (min length to max length) in an eccentrically activated sarcomere? - Graph A - Graph B - Graph C - Graph D

Graph A. Should be a negative relationship, with H-Zone length on the X-axis and Zone of Overlap Length on the Y-Axis. Yes! For this question you are asked to select a graph that depicts the effect of the H-zone on the zone of overlap. The zone of overlap is dependent (vertical axis) on the H-zone length (horizontal axis). For short H-zone lengths, the fiber is very shortened - this means that the Zone of overlap is maximized. For long H-zone lengths, this means that the fiber is very long and the zone of overlap is minimized (or if pulled long enough, 0 overlap)

Vitamin D is required for absorption of dietary calcium. Using the graphs, which graph best depicts the effect of increasing calcium intake (assume vitamin D present) on bone mass? - Graph B - Graph A - Graph D

Graph D. Right - the correct answer is D! Horizontal axis would be Vit D, vertical would be bone mass. When calcium levels are low, the body cannot build bone matrix (it can make collagen, but then it will not mineralize) and so bone mass will remain low. This means that graph A is out. Graph B & D both show increased bone mass with increasing dietary calcium and both have a plateau - this would mean that bone mass reaches a maximum regardless of dietary calcium and even if more calcium were available, bone mass could not further increase. This might be due to a maximum uptake of calcium or a maximum osteoblast activity or homeostatic regulation of blood calcium maxing out bone activity. But then, in Graph B, there is a decline in bone mass even though dietary calcium continues to be high - why would bone mass decrease with really high dietary calcium? Why would osteoclasts begin breaking down bone again, causing decreased bone mass?

In skeletal muscle cells, Ach opens chemically gated sodium channels. Ach is necessary for activating skeletal muscles cells - once activated, skeletal muscle cells produce force. Unlike neurons, skeletal muscle activations can build on one another, producing more and more force. Using the graphs, which graph best depicts the effect of increasing Ach release from neurons on skeletal muscle force? - Graph A - Graph B - Graph C - Graph D

Graph D. Right! Horizontal axis would be increasing Ach release from neurons, vertical would be skeletal muscle force. When more Ach is available, it will bind to receptors on the skeletal muscle cell. The more receptors bound, the more they activate the muscle cells, causing more force. The line goes up. However, receptors can be saturated. Once all the receptors are bound, no greater rates of sodium can enter the cell, causing a maximum activation of the muscle cell - this is shown best by graph D. The line plateaus and adding more Ach (horizontal axis) does not increase force (vertical axis).

Using the prior figure, where do you find the cells capable of producing osteoid? - H & O, but not N - O - N - H - All of the above

H & O, but not N H is the periosteum, O is the endosteum. Both contain a layer of osteoblasts, osteoclasts and osteogenic cells (also called osteoprogenitor cells). For the periosteum, it is as the inner layer, immediately against the compact bone, deep to the fibrous dense irregular connective tissue. Of these cells, the osteoblasts can produce osteoid; as they do so, they add bone through appositional bone growth. N is the hyaline cartilage - the chondrocytes there do not make osteoid.

Using this figure, where would you find canaliculi? - I & F but not M - F - I - M - All of the above

I & F but not M Yes. I is the compact bone, F is the spongy bone. Both contain lamellae with canaliculi - these are made of calcified matrix . Since the matrix is calcified, it limits nutrient diffusion. This is why canaliculi are present - to permit nutrients reach trapped cells (osteocytes trapped in lacunae are connected by the little channels, the canaliculi). M is the synovial lining of a joint capsule. It does not contain canaliculi.

You are a post-menopausal 65-year old female who has fallen and had a mid shaft fracture of your fibula (no ankle involvement). After assessing your injury, no surgery is required and your physician advises you that your fibula will heal on its own. You can walk, though it is painful (the fibula bears ~10% of body weight, the tibia bears the rest). To help you heal, your physician prescribes you take calcitonin (200 IU) per day. Using the data from class and what you may know, do you agree with your physician and wish to take the calcitonin, choose another medication or choose an alternate therapy? Support your position both using information about bone density from the graphs and what we have examined in class. Give at least 2 distinct reasons for your choice - these can include advantages or disadvantages of either your chosen option or the ones you did not want to choose. If you choose some alternate therapy, you must explain why it is a reasonable option given what we have learned in our class.

I would disagree with my physician that taking calcitonin is the best option because according to the graphs comparing hormones that help with bone healing, calcitonin had the lowest impact on bone mass density and it also took the longest time out of all the other medications to improve bone mass density. I would, instead, choose to take an estrogen supplement. This is because estrogen has the highest positive effect on increasing bone mass density and the time period it takes for estrogen to start improving bone mass density is only one year. On top of that, it may be beneficial to have an estrogen supplement to help with menopausal issues, such as heat flashes and inability to sleep.

On a certain neuron, neurotransmitter X (NT X) caused a hyperpolarization due to direct opening of an ion channel. When will NT X cause a depolarization on a different neuron?

If a different neuron has the receptor for NT X, but on a different ion channel Right! NT X may bind to a receptor associated with a K+ channel on one neuron, leading to a hyperpolarization. But on another neuron, that same receptor for NT X may be associated with a Na+ channel. Or a Ca++ channel. This is the beauty of receptor associations. While receptors are specific for specific ligands, they can be associated with many different proteins in/on the target cells, leading to differential responses in different cells. A great example is the NT acetylcholine - in the heart, it binds to its Ach receptor and causes hyperpolarization; at the gut, Ach causes depolarization.

Where do you find the cells that act to remodel or maintain bone? - In osteon lacunae - In the periosteum found covering bones - In the endosteum found lining the medullary cavity - Lining the central canal of the osteon - In all of the listed structures

In all of the listed structures. Right! Bone is a dynamic tissue that remodels in response to stress and hormones. Osteoblasts and osteocytes act to build bone, an important feature of bone remodeling. Osteoclasts chew old bone and remove it from where it is not needed. Bone remodeling reshapes the bone while bone maintenance redeposits and renews old bone. The endosteum is a layer of osteoblasts, osteoclasts and osteoprogenitor cells that actively remodel bone. The endosteum is located in the central canal and covering all the trabeculae inside a bone. It is adjacent to the medullary cavity as well. The periosteum consists of the same cells (inner layer of periosteum) although it is located on the outside of bone, adjacent to the outermost compact bone. When bones get thicker or thinner, it is by both endosteal and periosteal deposition or removal. Osteocytes maintain the matrix and can act to build new bone. All the cells mentioned are found in the endosteum and periosteum, although only osteocytes are located in lacunae.

For connective tissues compared to muscle tissues, are the proteins intracellular or extracellular? - In connective tissues, the proteins are extracellular - In connective tissues, the proteins are intracellular

In connective tissues, the proteins are extracellular. Right! In connective tissues, the majority of the tissue volume is extracellular materials. The proteins are located outside the tissue cells. These proteins include collagen, reticular fibers and elastic fibers.

Below represents data from four different clinical trials in which different medications were administered and lumbar spine bone mineral density was observed. For each clinical trial, medications and a placebo were given to postmenopausal women (treatment group, control group), except for the growth hormone trial in which growth hormone (or placebo) was administered to growth hormone deficient adult males age 24-63. All data shown are in relative reference to baseline bone mineral density recorded before trial onset. Using this image, what do these hormones/medications show? - Decreased bone density with treatments of growth hormone, calcitonin, bisphosphonates & estrogen - Increased bone density with treatments of growth hormone, calcitonin, bisphosphonates & estrogen - Decreased bone density with treatments of growth hormone and calcitonin, but increased bone density with bisphosphonates & estrogen - Increased bone density with treatments of growth hormone and calcitonin, but decreased bone density with bisphosphonates & estrogen

Increased bone density with treatments of growth hormone, calcitonin, bisphosphonates & estrogen Right! All graphs show increased bone mineral density in the controlled trials for participants compared to a placebo. This indicates that giving growth hormone, estrogen, bisphosphonates or calcitonin to these populations will increase bone mineral density.

What type of tissue growth is occurring inside the circled area shown? - Interstitial growth - Appositional growth

Interstitial growth. Right. The circle indicates the area within the hyaline cartilage of the growth plate. Since the tissue is experience mitosis and matrix deposition here, deep within the tissue, this is interstitial growth. If the tissue were being deposited on the periphery, that would be appositional growth.

Skeletal muscle requires a neural signal for activation. The neurotransmitter that always activates skeletal muscle is Acetycholine (Ach). How does Ach excite skeletal muscle cells? - It crosses the sarcolemma through chemically gated channels - It binds to chemically gated channels on the sarcolemma - It activates chloride channels on the sarcolemma

It binds to chemically gated channels on the sarcolemma. Right! Like other synapses, the neuromuscular junction (the place where the neuron releases neurotransmitter to the skeletal muscle cell) involves neurotransmitter binding to chemically gated channels. Ach does not cross the sarcolemma (cell membrane of muscle cells) nor does it enter skeletal muscle cells. If Ach did open chloride channels on the sarcolemma, the skeletal muscle cell would hyperpolarize. you do not know this quite yet, but skeletal muscle cells have voltage gated channels and can generate action potentials. They do in the same way neurons do - they reach threshold and then fire APs. Opening Cl- channels would make the muscle cell less likely to fire and AP and contract.

What happens to titin during skeletal muscle shortening? - It compresses - It stretches - It slides past the thin filament

It compresses. Right! Inside skeletal muscles, titin is a protein of the thick filament. It runs through the myosin component of the thick filament, spanning from Zdisc to Zdisc within a sarcomere. Acting to anchor the thick filament, it has a spring like quality in which it compresses during shortening and stretches during lengthening. Titin allows skeletal muscle sarcomeres to maintain their shape, keeping thick and thin filaments in proper alignment.

This figure shows the levels of sex hormones (estrogen and testosterone) from birth to old age. Estrogen in women is the solid purple line; Testosterone in men is the dotted green line. Using this figure, why are men less likely to suffer osteoporosis than women? - Men's adult sustained levels of sex hormone continue to stimulate osteoblasts preventing osteoporosis - In women, estrogen stimulates osteoclasts, but testosterone does not, so the male skeleton has less bone removal - In later adulthood, the high peak of female sex hormone produces more remodeling of bone, which weakens the skeleton in women

Men's adult sustained levels of sex hormone continue to stimulate osteoblasts preventing osteoporosis Right! In women, menopause occurs when the ovarian cells that produce estrogen are gone. Both estrogen and testosterone stimulate osteoblasts, but have no effect on osteoclasts. Osteoporosis occurs when osteoclast activity is greater than osteoblast activity. With the loss of estrogen in women, there is less stimulus for osteoblast activity, although the osteoclasts continue their level of activity. The skeleton weakens and may develop osteoporosis if severe enough. In men, the presence of testosterone throughout life continues to promote osteoblast activity, and therefore, the skeleton remains stronger.

During formation of the flat portions of the frontal bone (the bone that makes up your forehead), ______ differentiate to become _______. - mesenchymal cells; osteoblasts - osteoblasts; osteoclasts - osteoprogenitor; osteoclasts - mesenchymal cells; chondroblasts

Mesenchymal cells, osteoblasts. Right! Certain bones form intramembranously - these include the flat skull bones of the cranium, the clavicle and the mandible. During intramembranous bone formation, mesenchymal cells in the mesenchyme differentiate to become osteoblasts. Differentiation refers to a non-specific stem cell developing into a specific cell type. Mesenchyme in the embryo is a tissue that contains mesenchymal cells and extracellular fibers and fluid. During development, specific cellular signals cause the mesenchymal cells in the appropriate areas to cluster and then differentiate into osteoblasts. The newly formed osteoblasts deposit bone which eventually morphs into the above mentioned bones. Osteoblasts are derived from osteoprogenitor cells which are derived from (differentiate from) mesenchymal cells. Chondroblasts are also derived from mesenchymal cells, but they deposit cartilage, not bone. This process occurs during endochondral bone formation. Osteoprogenitor cells do not give rise to osteoclasts - the bone destroying cells. While osteoclasts are active during bone growth and remodeling, they are derived from the white blood cell line, not the osteoprogenitor cell line.

After a bone fracture, bone repair occurs. Depending on the severity of the break and the distance between the bone fragments, bone healing can occur in two ways: direct and indirect bone healing. With direct bone healing, the broken elements must be very close together and osteoblasts present at the site of injury deposit concentric lamellae around blood vessels. Indirect bone healing occurs when bone fragments are further apart. Initially, a large vascular response occurs, bringing cells and nutrients to the site of injury. Then, a temporary bridge (patch) forms. The temporary patch consists of cells and collagen fibers in a gelatinous, avascular matrix. The patch is then replaced by woven, trabecular bone but is later remodeled into mature bone. This type of bone repair can occur in spongy or compact bone and involves many cell types.Using the passage, during indirect and direct bone healing in the normal, healthy adult aged 40, which of the following would be recommended to help repair a fractured bone? - a drug that blocked the action of calcitonin - moderate weight bearing activity - a drug that blocked the action of parathyroid hormone - limited exposure to sunlight

Moderate weight bearing activity. During bone healing, you will want to promote osteoblast activity and bone remodeling. This means that you will want to have some activity and not inhibit any hormones needed for good bone health. Calcitonin and PTH have impacts on osteoblasts and osteoclasts, and unless they are out of balance, you would not want to interfere with their normal influence on bone. Since fracture repair involves remodeling as a normal part of the process, you will want activity of osteoblasts and osteoclasts. Vitamin D is needed for calcium absorption in the gut - exposure to sun light is needed for production of vitamin D. Again, you would not want to interfere with its normal activity.

Mature osseous connective tissue (bone) is composed of collagen fibers and mineralized matrix. When osseous CT is first made, the osteoblasts secrete osteoid onto which calcium salt then precipitates. What is osteoid? - Mostly collagen or collagen pre-cursors - Hydroxyapatite mineral - Hyaline cartilage - Mesenchyme

Mostly collagen or collagen pre-cursors. Right! Osteoid is the immature bone that is first formed. It contains the collagen fibers and proteins that promote calcium salt formation onto the collagen. Hyaline cartilage is a different connective tissue that makes embryonic protoskeletons and articular cartilage. Mesenchyme is an embryonic connective tissue made of mesenchymal cells in a liquid ground substance. Hydroxyapatite mineral is the calcium salt that then forms on the osteoid.

Neurons are specialized for communication. They are capable of sending electrical signals due to the presence of many ion channels and pumps on the cell membrane that they constantly maintain or replace as needed. Which of the following would be NOT consistent with this information?

Neurons are anucleate (they do not have nuclei) Right! Neurons (nerve cells) are very active tissue cells that send signals throughout your body. For the nervous system to communicate with a muscle cell or gland, a nerve cell must physically extend all the way to the target. Along the length of the nerve cell, the cell membrane is populated with many ion channels and pumps (pumps move substances against a concentration gradient and require energy to operate). These pumps and channels are proteins that the neuron must construct for itself and insert into the cell membrane. To make these membrane proteins, the neuron uses its abundant rough ER and its nucleus. There are so many rough ER in neurons they have a special name - Nissl bodies - named for a German neurologist. The presence of the many ion pumps in a neuron means that the neuron uses lots of ATP. A full 2/3rds of neuron ATP use is for these pumps alone! The nucleus is required for the production of the membrane proteins (by directing the cell to make these proteins or expressing the recipe for the proteins themselves). Anucleate means "without a nucleus" and this would be inconsistent with the needs of the neuron. The only anucleate cell that we talk about is the red blood cell and it does have a nucleus for a time during its lifespan (the time when protein production is occurring).

Your heart pumps blood at variable rates depending on your degree of physical activity or neural/hormonal activity (this is called heart rate). With exercise or fear, heart rate increases to pump more blood to an active body. Yet after exercise, heart rate decreases to a resting level. There are several nerves and hormones that stimulate heart rate to increase as needed, or decrease when needed, but there is no receptor that monitors heart rate. Is heart rate homeostatically regulated?

No. Correct! Homeostatic regulation requires 3 components: a receptor, a control center and an effector. Without a receptor, there cannot be homeostatic regulation. Even though it seems that heart rate varies and returns to some number, this is not technically homeostatic regulation. Blood pressure is homeostatically regulated - it has baroreceptors that monitor pressure, the brainstem that receives the information and nerves that then activate blood vessels to contrict or dilate to correct pressure (as well as other effectors) - but heart rate is not. Heart rate is not monitored by any neuron. Absolute water content of the body is not homeostatically regulated either - no neuron detects the number of water molecules, although neurons do detect the relative saltiness of the body. This is why different people can have the same blood pressure and fluid concentration but very different overall blood volume or heart rate.

If mature RBCs do not have mitochondria, can they make ATP aerobically?

No. No they can not. Aerobic ATP production is due to mitochondrial activity. Without mitochondria, there is no aerobic ATP production.

Using figure 1, what type of stimulus would generate another action potential during C & D?

None. Correct. This is the absolute refractory period. The sodium voltage gated channels are either in use or not yet reset and so a second action potential cannot be generated despite a new large signal being applied.

In neurons, a stimulus is an event that changes membrane potential. What would create "a bigger" or "stronger" stimulus on a neuron?

Opening a chemically gated channel for a longer time Opening more chemically gated channels at once Right! Changes in transmembrane potentials can be made bigger or stronger by allowing more ions to cross the membrane. We can have more ions cross the membrane when gated channels are left open for longer or when more gated channels are opened at once.

After a bone fracture, bone repair occurs. Depending on the severity of the break and the distance between the bone fragments, bone healing can occur in two ways: direct and indirect bone healing. With direct bone healing, the broken elements must be very close together and osteoblasts present at the site of injury deposit concentric lamellae around blood vessels. Indirect bone healing occurs when bone fragments are further apart. Initially, a large vascular response occurs, bringing cells and nutrients to the site of injury. Then, a temporary bridge (patch) forms. The temporary patch consists of cells and collagen fibers in a gelatinous, avascular matrix. The patch is then replaced by woven, trabecular bone but is later remodeled into mature bone. This type of bone repair can occur in spongy or compact bone and involves many cell types.Using the passage, what structures are formed during direct fracture healing? - osteons - cancellous bones - soft calluses - articular cartilages

Osteons. The passage states: With direct bone healing, the broken elements must be very close together and osteoblasts present at the site of injury deposit concentric lamellae around blood vessels. This describes osteons but not articular cartilages or soft calluses which are both cartilaginous. Cancellous bone is another name for spongy bone which do not contain concentric lamellae around a blood vessel - the lamellae are irregular in spongy/cancellous bone.

Tendons are a connective tissue. They have many collagen fibers. Which of the following best describes where these fibers are located? - Outside the tendon cells, in the extracellular matrix - In the cytosol of the cells of the tendon

Outside the tendon cells, in the extracellular matrix. Correct! The fibers of connective tissues are part of the extracellular matrix (outside the cells). Ground substance refers to the non-fiber part of the extracellular matrix. Fibroblasts are the cell type found in tendons (dense regular connective tissues) and they are responsible for producing the collagen fibers. Chondrocytes are cartilage cells and are not found in tendons, they are found in cartilaginous structures like the ends of bones, intervertebral discs and knee menisci. Osteocytes are bone cells; adipocytes are fat cells. All of these are connective tissue cells, just of different connective tissues.

According to this figure, what gland is the primary controller for regulating blood calcium? - Parathyroid gland - Thyroid gland

Parathyroid gland. Right! The parathyroid glands are small glands attached on the posterior of the thyroid gland. They secrete parathyroid hormone (PTH) which is the primary regulator of blood calcium level in the adult. PTH is released when blood calcium falls, and PTH stimulates osteoclasts to break down more bone. When bone is destroyed, the liberated calcium enters the blood, raising the blood calcium levels. This graph shows that blood calcium level changes greatly when the parathyroids are removed. When the thyroid is removed, there is no effect on blood calcium. Although this graph is a dramatization, the effect has been observed in practice with thyroidectomy and parathyroidectomy. While the thyroid gland does secrete a hormone called calcitonin, it is not important in regulating adult blood calcium. It is more important during growth, and especially important in other vertebrates (like mice), but not so in human. Removal of the parathyroid glands would be most devastating to blood calcium balance for these reasons.

The skeletons of newborn children lack the bony processes where muscles attach, though they form in the first years of life. Which of the following best explains how and where these processes develop? - Tendons release growth hormone and calcitonin which activates nearby osteoblasts - Interstitial bone formation occurs in response to physical stresses generated by tendons - Periosteal osteoblasts are stimulated by physical stresses generated by tendons - Endosteal osteoclasts detect the location of tendons and secrete less acid

Periosteal osteoblasts are stimulated by physical stresses generated by tendons. Right! Physical stress stimulates osteoblasts to deposit bone. Tendons attach at the periosteum. Increased physical stress at the periosteum stimulates the osteoblasts to make more bone at that site. Interstitial bone formation does not occur at the periosteum (site of tendon attachment); the endosteum is not where tendons attach; although it may seen popular to select that tendons release GH & calcitonin, this is not true - you should know that calcitonin is released by the thyroid gland.

Which of the following will most likely stimulate an action potential in a neuron?

Several small depolarizations, occurring repeatedly near the trigger zone Right! Depolarizations bring the neuron transmembrane potential above resting values towards (or above) threshold values. Once threshold is reached at the trigger zone, the voltage gated channels open and an action potential can be generated. Hyperpolarizations lower the membrane potential away from threshold and make a neuron less likely to fire an action potential. In this question I ask which is most likely but, what you do not know from this question is the magnitude of each stimulus. They could be very small depolarizations and very large hyperpolarizations - truthfully, it is impossible to know if the postsynaptic neuron generated an action potential without seeing a measure of its membrane potential at the trigger zone.

What do we call the process whereby a molecule crosses the cell membrane, moving from a high concentration of itself to a low concentration of itself, by dissolving through the phospholipid portion of the cell membrane? (Select the single best answer that describes this specific circumstance.)

Simple Diffusion Correct! Simple diffusion refers to the passive (no ATP required) movement of a molecule through a cell membrane. The molecule must be able to penetrate the membrane without using a transport protein. When it moves, it does so by moving away from an area of high concentration of itself to an area of low concentration of itself. Examples include oxygen, carbon dioxide, steroid hormones and fat soluble vitamins A, D, E & K which all dissolve across the membrane into or out of the cell. Small, non-charged polar molecules can do this too: alcohol, urea and glycerol are included in this. If the molecule cannot pass through the membrane except by using a transmembrane protein, but does so without ATP because it goes from high concentration to low (down a concentration gradient), this is said to be facilitated diffusion. It is still a passive process, but not simple. Roughly, if the membrane protein changes shape as this happens, it is a carrier; if the membrane protein does not, it is a channel. Passive transport is too broad of a term in this specific instance above, because either simple diffusion or facilitated diffusion are both passive transport. Active transport happens when molecules move against their concentration gradients across the cell membrane using membrane transport proteins. This type of movement against a concentration gradient, from low concentration to high, always requires ATP. This is why we call it active. Examples include membrane pumps that pull sodium ions out of the cell and deposit them on the outside of cells. Because of the action of these pumps, sodium is always more concentrated outside cells than in. Although endocytosis and exocytosis use ATP, we do not call them active transport usually, preferring the term vesicular transport.

What is the difference between spongy bone and compact bone? - Spongy bone and compact bone are microscopically arranged differently - Spongy bone and compact bone are made of different matrix material - Spongy bone and compact bone contain different cellular populations - Spongy bone and compact bone are both absent in long bones.

Spongy bone and compact bone are microscopically arranged differently. Right! Spongy bone and compact bone are made of the same matrix material (1/3rd collagen, 2/3rds mineral), contain the same cellular populations (osteoblasts, osteoclasts, osteocytes, osteoprogenitor cells) and are both found in long bones. Microscopically, the matrix arranges itself as osteons in compact bone, but as non-osteon, irregular lamellae of trabeculae in spongy bone.

Suppose you step on a nail. What layer of the epidermis do you penetrate first? - Stratum corneum - Stratum granulosum - Stratum germinativum - Stratum spinosum

Stratum corneum. Right! From bottom to top, the layers are stratum germinativum, stratum spinosum, stratum granulosum, stratum lucidem, stratum corneum. When a nail enters, it goes through the top (apical) layer first, then hits the basal layer last.

Suppose you are a cytologist and you are examining a cell under the microscope. You observe that inside the cell there are many flattened, sac-like structures, many of them with small round granules. Based on this information, which of the following conclusions would be most logical?

The cell produces many proteins for export. Right! The best answer here is that the cell makes proteins for export. The description given in the question is suggestive of an organelle that has flat sacs and ribosomes attached to them - the rough endoplasmic reticulum (rough ER). This organelle is responsible for protein production. These proteins might leave the cell or become incorporated into the cell membrane. The other options in this question may be true, but the only information you were given was about the rough ER and the question states Based on this information... It would not be logical to conclude no cell membrane - the cell would not be in very good shape to examine in the scope without a cell membrane. There was no mention of a flagellum or of centrioles, therefore motion and cellular division are unusual conclusions at best.

Which of the following would be most likely found in a cell that is subjected to significant mechanical strain (such as a cell in the outer skin)?

The cell would have many cytoskeletal elements Yes! Keratin is a protein string (cytoskeletal element) found in great quantity in skin cells. The keratin provides strength to skin cells to resist mechanical stresses. The keratinized skin cells are regularly lost from the body surface and replaced with cells in deeper layers of the skin. Smooth ER is used for making fats or carbohydrates (or combinations of those) or acts as an intracellular storage site. It is not the best choice here. Golgi are not the best choice here because they serve to repackage materials that do not remain in the cytoplasm. Phospholipids contribute significantly to the cell membrane and without them, the cell is unlikely to be functional. In answering questions you must always assume a healthy adult unless otherwise indicated.

Which of the following would be most likely found in a cell that is subjected to significant mechanical strain (such as a cell in the outer skin)? - The cell would have many golgi apparatuses - The cell would have many smooth ER - The cell would lack phospholipids in its cell membrane - The cell would have many cytoskeletal elements

The cell would have many cytoskeletal elements. Yes! Keratin is a protein string (cytoskeletal element) found in great quantity in skin cells. The keratin provides strength to skin cells to resist mechanical stresses. The keratinized skin cells are regularly lost from the body surface and replaced with cells in deeper layers of the skin. Smooth ER is used for making fats or carbohydrates (or combinations of those) or acts as an intracellular storage site. It is not the best choice here. Golgi are not the best choice here because they serve to repackage materials that do not remain in the cytoplasm. Phospholipids contribute significantly to the cell membrane and without them, the cell is unlikely to be functional. In answering questions you must always assume a healthy adult unless otherwise indicated.

Using figure 1, what is happening during time period C?

The membrane is more permeable to sodium than it is to potassium Correct! The voltage gated Na+ channels are open at this time and allowing Na+ to enter the cell causing depolarization. Opening gated channels increases membrane permeability. The faster those channels open, the faster permeability increases. Closing the channels decreases permeability.

In which of the following would you expect to find osteons? - The diaphyseal cortex of the humerus - The medullary (marrow) cavity of the femur - The trabeculae of the humeral distal epiphysis - The ligaments connecting adjacent vertebrae - The epithelium of the oral cavity

The diaphyseal cortex of the humerus. Right! Osteons are the structural unit of compact bone. They make up the thick walls of long bone diaphyses and the most superficial compact bone collar (cortex) of long bone epiphyses. Compact bone is found in all bones with variable amounts of spongy bone between compact bone regions. Osteons do not exist in the ligaments of the neck (a dense regular connective tissue) or in epithelia. The medullary (marrow) cavities of long bones contain bone marrow (red or yellow, more likely yellow). Perhaps you selected the trabeculae within an epiphysis. Trabeculae are spongy bone struts. While spongy bone is made of the same material as compact bone, the organization is different and osteons do not form. It is important to remember the terms epiphysis and diaphysis - we will use them more when we talk about how bone grows.

In bones, a layer of osteoblasts and osteoclasts line the interior of the bone (this cellular layer covers all trabeculae, is adjacent to the medullary cavity and lines the inside of osteons). This layer is called the endosteum. What is its role in bone? - The endosteum can add or remove bone from the inside of bones, remodeling them. - The endosteum can add or remove cartilage from the inside of bones, replacing bone with cartilage. - The endosteum is an epithelial layer that protects the inside of bones and regulates transportation of nutrients to bones. - The endosteum has collagen fibers that anchor attaching muscles.

The endosteum can add or remove bone from the inside of bones, remodeling them. Right! The endosteum is made of connective tissue cells (not epithelial cells) that can deposit or reabsorb bone from the internal aspect of the bone. During growth, the endosteum is particularly important to remodel bone from the inside. Without endosteal bone reabsorption, as bones grow wider overall, the bone would become too heavy. In other words, as bones grow wider (due to periosteal bone deposition), they maintain the same cortical bone thickness because of endosteal removal. Cartilage is deposited by chondroblasts. Muscles attach at the outside of bone on the fibrous layer of the periosteum.

What ligament passes from the scapula to the humerus to reinforce the shoulder joint? - The glenohumeral ligament - The acromioclavicular ligament - The coracoclavicular ligament - The coracoacromial ligament

The glenohumeral ligament. Right! This question is more about your understanding that the names of structures (in this case ligaments) can be "dissected" to figure out where the structures are on the body. It is easy to get overwhelmed by information, but if you remember that the clavicle, humerus and scapula articulate to make the pectoral girdle/shoulder, then you can reason out these names. The glenohumeral ligament goes from the glenoid fossa/cavity of the scapula to the humerus. The coracoclavicular ligament goes from the coracoid process of the scapula to the clavicle. The acromioclavicular goes from the acromion process of the scapula to the clavicle. The coracoacromial goes from the coracoid process to the acromion process of the scapula. So really, just remembering the names of the acromion and coracoid processes of the scapula, the clavicle and the humerus is all that is needed to answer this question. You will find that learning the bones well will help you throughout the rest of the term and course in general.

In an infant's humerus, what happens if the rate of hyaline cartilage death is faster than the rate of cartilage interstitial growth? - Nothing - this would not affect humerus development. - The humerus would become too short at full maturity. - The humerus would become too long at full maturity.

The humerus would become too short at full maturity. Right! The humerus is a long bone that grows through endochondral bone formation. During endochondral bone formation hyaline cartilage grows on one aspect of the epiphyseal plate (epiphyseal side) as it dies on the other (diaphyseal side). As it dies, it is degraded and replaced by bone. If the rate of growth is slower than the rate of death and replacement, the bone will replace the existing cartilage completely. Because bone is a hard tissue, it cannot grow from within (interstitial growth) to further elongate the bone and thus a long bone cannot grow any longer once the cartilage at the plate is gone. Too fast cartilage death is a problem in certain forms of dwarfism that results in smaller stature.

Which are cartilaginous joints?(You may want to use your lecture notes or textbook tables for this one.) - The sacroiliac and the joint between the arches of adjacent vertebrae - The joint between the pubes and the joint between the bodies of adjacent vertebrae - The distal tibia-fibular joint and interosseous membrane of the tibia/fibula - Gomphoses joints & the elbow and wrist - All of the listed joints are cartilaginous

The joint between the pubes and the joint between the bodies of adjacent vertebrae Right! The joint between the pubes and the joints between adjacent vertebral bodies are cartilaginous joints - more specifically, they are amphiarthroses, cartilaginous symphysis joints. That is, they allow little movements and contain a disc (puck/pad) of fibrocartilage between the articulating bones. The sacroiliac and the joint between the arches of adjacent vertebrae (joint at the superior and inferior articular processes) are synovial. Although we do not typically think these joints as mobile as perhaps the shoulder, they are lined with synovial membranes and thus are synovial joints. The gomphoses, the joint between the distal tibia/fibula and the interosseous membranes are all fibrous. The elbow and wrist joints are diarthroses, synovial joints (elbow is hinge, wrist is condylar/condyloid).

Which are cartilaginous joints? - The joint between the pubes and the joint between the bodies of adjacent vertebrae - The sacroiliac and the joint between the arches of adjacent vertebrae - Gomphoses joints & the elbow and wrist - All of the listed joints are cartilaginous - The distal tibia-fibular joint and interosseous membrane of the tibia/fibula

The joint between the pubes and the joint between the bodies of adjacent vertebrae. Right! The joint between the pubes and the joints between adjacent vertebral bodies are cartilaginous joints - more specifically, they are amphiarthroses, cartilaginous symphysis joints. That is, they allow little movements and contain a disc (puck/pad) of fibrocartilage between the articulating bones. The sacroiliac and the joint between the arches of adjacent vertebrae (joint at the superior and inferior articular processes) are synovial. Although we do not typically think these joints as mobile as perhaps the shoulder, they are lined with synovial membranes and thus are synovial joints. The gomphoses, the joint between the distal tibia/fibula and the interosseous membranes are all fibrous. The elbow and wrist joints are diarthroses, synovial joints (elbow is hinge, wrist is condylar/condyloid).

In the body we identify four primary tissue types: epithelial tissue, muscle tissue, connective tissue and neural tissue. Epithelial tissues usually share an embryological origin and are located over external body surfaces (epidermis from the ectoderm), lining body cavities and hollow organs (stomach, lungs, bladder, etc from the endoderm), and make up glandular tissue throughout the body (exocrine sweat, mammary glands derived from the ectoderm, as well as endocrine glands like thyroid, pancreas, etc derived from the endoderm). In this first model, you will investigate the structure of epithelial tissues. Shown here are 6 types of epithelia - the name of each type of epithelium is written below the tissue shown. Looking at the tissues, how are stratified epithelia different from simple epithelia? - the shape of the cells - the number of layers of cells

The number of layers of cells. Yes. Stratified epithelia have several cells stacked up from the bottom of the layer to the top. Simple epithelia have only one cell thickness from the top to the bottom of the epithelial layer.

When you swim in the ocean you lose water. What most likely explains this observation?

The ocean water is relatively saltier than the inside of your body (and cells) Correct! Water moves passively (does not require cellular energy to move) to a place where there is less water (relatively). When we say less water, it is not in absolute terms, but instead we are talking about concentrations. If a liquid has lots of salt and little water, we say that solution is very concentrated in salt but it has relatively little water. If another solution has little salt (or other dissolved substance, like sugar) we say it is dilute and has relatively much water. A swimming pool is very dilute and compared to the inside of your body, it has fewer dissolved particles for each molecule of water. Therefore water moves away from where there is more water (in the pool) to where there is less (your body) - water enters your body and makes your body swollen. The ocean is very salty - it has many dissolved salt particles for each molecule of water. When you swim in the ocean, you lose water to the ocean because the leaving water is trying to "dilute" the ocean's salt. This process is osmosis and it occurs across every body cell. In response to wet conditions, you skin wrinkles. Interestingly, this is due to neural activation - if the nerves are cut, you skin does not wrinkle (or prune) despite the presence of external water. It is believed this response increases finger grip in wet conditions.

Skeletal muscle cells generate action potentials. Which of the following is most likely FALSE about skeletal muscle cells? - The sarcolemma contains voltage gated potassium channels - The sarcolemma contains voltage gated sodium channels - The sarcolemma has voltage gated calcium channels - The sarcolemma has sodium potassium pumps

The sarcolemma has voltage gated calcium channels. Correct! To be able to generate action potentials, cells must have the proper density of voltage gated sodium and voltage gated potassium channels. These are the structures that determine the function. They must also have a concentration gradient across the cell membrane for sodium and potassium - all cells have this gradient because all cells in your body have the sodium and potassium pumps on their cell membranes. Voltage gated calcium channels are not necessary for action potential generation - they are necessary for NT release from the synaptic vesicles. These vesicles are present in neurons, but not in skeletal muscle cells.

Using figure 1, what is happening during C & D?

The sodium voltage gated channels are either open or are incapable of opening. Correct! This is the absolute refractory period. A second action potential is not possible.

The periosteum is a double layered structure on the outside of all bones. The outermost layer is a fibrous connective tissue, the innermost layer (adjacent to the cortical bone) is a layer of osteoblasts, osteoclasts and osteogenic/osteoprogenitor cells. What are the two roles of the periosteum? - The outer fibrous layer attaches muscle; the inner cellular layer deposits or removes bone - The outer fibrous layer deposits or removes bone; the inner cellular layer attaches muscle - The outer fibrous layer makes the bone flexible; the inner cellular layer regulates nutrient/waste transfer - The outer fibrous layer regulates nutrient/waste transfer; the inner cellular layer makes the bone flexible

The outer fibrous layer attaches muscle; the inner cellular layer deposits or removes bone. Right! The periosteum's outermost layer is a dense irregular connective tissue in which collagen fibers are oriented at varying angles (hence the name, dense - lots of fibers; irregular - fibers at many angles). This creates good tensile strength to resist the pull of the many muscles attaching at different angles. The collagen fibers in this layer blend with the fibers of muscle tendons and with the outermost compact bone. By blending together, the muscles attach very firmly to both the periosteum, which is then firmly anchored to the bone - it is more typical to tear a muscle in the middle of its belly than to tear it off the periosteum. The name of the connecting fibers between the periosteum and bone are called Sharpey's fibers. The cells of the inner periosteal layer are essential for bone remodeling. As bones grow in length, they need to add mass to the outer circumference of a bone and they need to be able to remove bone where it is not needed. Bone is alive and requires resources to maintain it. The periosteum helps balance the needs of the body for strong bones that are of the right construction for maximal efficiency of use.

Which of the following happens during formation of the femur? - Osteoid deposition occurs before the appearance of blood vessels - The outer periosteal bone forms before the inner spongy bone - The epiphyses ossify before the diaphysis - Cartilage cells are converted into osteoblasts

The outer periosteal bone forms before the inner spongy bone. Right! The femur (like all long bones) forms via endochondral bone formation. During endochondral bone formation hyaline cartilage must die and be removed before osteoblasts can produce new bone on the remains of the cartilage. This bone deposition occurs at the outer edges of the structure to create a bony collar around the diaphysis. The osteoblasts depositing this bone must arrive via the invading blood vessel because cartilage cells cannot transform into bone cells. So, blood must precede bone in the case of endochondral bone formation. When long bones form, the diaphysis is the first site of bone formation. At birth, the diaphysis is usually bone but the epiphyses are still cartilage. The epiphyses ossify (creating secondary ossification sites) at different ages throughout childhood. The skeleton can be dated by the pattern of secondary ossification sites. See here for an authoratative listing of the ages at which the these centers

When you swim in a pool, your body gains water. What most likely explains this observation?

The pool water is relatively less salty than the inside of your body (and cells). Correct! Water moves passively (does not require cellular energy to move) to a place where there is less water (relatively). When we say less water, it is not in absolute terms, but instead we are talking about concentrations. If a liquid has lots of salt and little water, we say that solution is very concentrated in salt but it has relatively little water. If another solution has little salt (or other dissolved substance, like sugar) we say it is dilute and has relatively much water. A swimming pool is very dilute and compared to the inside of your body, it has fewer dissolved particles for each molecule of water. Therefore water moves away from where there is more water (in the pool) to where there is less (your body) - water enters your body and makes your body swollen. The ocean is very salty - it has many dissolved salt particles for each molecule of water. When you swim in the ocean, you lose water to the ocean because the leaving water is trying to "dilute" the ocean's salt. This process is osmosis and it occurs across every body cell. In response to wet conditions, you skin wrinkles. Interestingly, this is due to neural activation - if the nerves are cut, you skin does not wrinkle (or prune) despite the presence of external water. It is believed this response increases finger grip in wet conditions.

Using figure 1, what is happening during C & D?

The sodium voltage gated channels are either open or are incapable of re-opening. Correct! This is the absolute refractory period. A second action potential is not possible.

What is the relationship between the muscles crossing a joint and that joint's properties (ie: joint stability, mobility or range and type of motion)? When answering this question, assume muscles are balanced on all sides of the joint. - The stronger the muscles crossing a joint, the more likely that joint is to dislocate - The fewer muscles crossing a joint, the more types of motions a joint can create - The weaker the muscles crossing a joint, the less range of motion that joint has - The stronger the muscles crossing a joint, the more stable the joint

The stronger the muscles crossing a joint, the more stable the joint Correct! Muscles stabilize joints, just as does more bony contact between elements, stronger ligaments, or more fibrocartilaginous elements (labrum, menisci). When the joint is more supported by muscles, it tends to have a lower range of motion but it is more stable. In addition, having more muscles, or longer muscles can increase the types of joint movements. When fewer muscles cross a joint, the joint cannot move in directions for which a muscle does not pull them.

After a bone fracture, bone repair occurs. Depending on the severity of the break and the distance between the bone fragments, bone healing can occur in two ways: direct and indirect bone healing. With direct bone healing, the broken elements must be very close together and osteoblasts present at the site of injury deposit concentric lamellae around blood vessels. Indirect bone healing occurs when bone fragments are further apart. Initially, a large vascular response occurs, bringing cells and nutrients to the site of injury. Then, a temporary bridge (patch) forms. The temporary patch consists of cells and collagen fibers in a gelatinous, avascular matrix. The patch is then replaced by woven, trabecular bone but is later remodeled into mature bone. This type of bone repair can occur in spongy or compact bone and involves many cell types.Using the passage, during indirect bone healing, what likely happens before the woven, trabecular bone is deposited? - the temporary patch is destroyed - cells of the patch differentiate into osteoblasts - Osteoid deposition occurs before the appearance of blood vessels - parathyroid hormone activates osteoclasts

The temporary patch is destroyed. Right! According to the passage: The temporary patch consists of collagen fibers in a gelatinous, avascular matrix. This implies cartilage. In order for bone to be deposited, the cartilage must be removed and then bone laid down. Cartilage cells cannot differentiate into osteoblasts; PTH was not mentioned in the passage; osteoid deposition must occur, but blood vessels are already there (as indicated in the passage). Indirect bone healing is much like endochondral bone formation and is described in our lecture notes and textbook. Direct bone healing is not described in our book, but is posted in the lecture 8 notes page on Canvas.

What characteristic unites all connective tissue? - They all come from a common embryonic tissue (mesenchyme) - They all have a rich blood supply - They all have osteocytes - They all have liquid ground substance

They all come from a common embryonic tissue (mesenchyme) Right! Connective tissues vary widely in anatomy. Some have many collagen fibers (dense regular connective tissues), some have few fibers (blood). Some are solids (bone) some are loose and stringy (areolar CT). The single unifying component among all connective tissues is their common originating tissue - all connective tissues come from a stem cell tissue called mesenchyme. Mesenchyme is found in embryos - it is made of mesenchymal cells and a fluid ground substance with a few fibers. These cells can differentiate to become bone cells or cartilage cells or blood cells or any other connective tissue cell. Not all connective tissues have a rich blood supply - cartilage is avascular and this is why it is slow to heal. Not all connective tissues have a hard ground substance - bone does, but blood is all liquid. Bone has osteocytes - they are the cells of bone (osteo=bone, cyte=cell). It is those cells that make the fibers in bone.

Mature red blood cells lack nuclei and mitochondria. Which of the following is consistent with this information?

They cannot add new transport proteins to their cell membranes Without nuclei, they cannot make new proteins. Since new membrane bound proteins would require a nucleus, rough ER & golgi, these cells cannot make such transport proteins. Additionally, mature RBCs are not able to repair their cell membranes, which is why we removed damaged cells and make new ones constantly. Though at some point in these cells' development these organelles were present. RBCs do not readily alter their membrane permeability to oxygen - since oxygen is fat soluble, it is freely permeable to the cell membrane. All cells have sodium/potassium pumps on their membranes that create concentration gradients for Na+ & K+. These pumps pump 3 Na+ out of the cell and 2 K+ into the cell. Because the membrane is not freely permeable to the charged ions, a differential ionic distribution of Na+ & K+ is created. RBCs can make ATP anaerobically, using glycolysis. This does not require mitochondria or oxygen, making RBCs excellent carriers of oxygen.

What changes occur in the epidermal keratinocytes as they migrate from the stratum basale (germinativum) to the stratum corneum? - They dehydrate, die and become full of actin - They swell, die and become full of calcitonin - They swell, die and become full of calcitriol - They dehydrate, die and become full of keratin

They dehydrate, die and become full of keratin Right! The keratinocytes die as they move from their nutrient source (dermal capillaries), dehydrate and become packed with keratin. Keratin is an intracellular protein that gives mechanical strength to keratinocytes. Calcitonin is a hormone made by the thyroid gland. Calcitriol is the active form of vitamin D and is not stored in skin cells. Actin is of course a contractile protein located in great abundance in muscle cells.

Glucose and oxygen are used by cells to produce energy for muscle action - this process occurs within each cell. Your new workout partner tells you that the supplement he's taking allows him to produce more energy (and have a better workout) because it increases oxygen delivery by increasing the number of cell membrane protein carriers for oxygen (such protein carriers transport substances from the outside of cells to the inside across the cell membrane). What would you say to him?

This seems unlikely because oxygen does not require membrane proteins for transport across the cell membrane. Correct! Oxygen is fat soluble and moves through the cell membrane unassisted. Only substances that cannot dissolve in the cell membrane require membrane proteins (channels or carriers) to cross the membrane. Such substances include charged ions (sodium, potassium, calcium) and molecules like glucose and amino acids. However, if a supplement increased the number of glucose transport proteins in a cell membrane, it would increase the number of glucose molecules that enter a cell. In our bodies, cells frequently change the number of transporters or receptors for specific molecules to increase transport in/out of a cell or the likelihood of reaction a cell has to a substance.

How do mature red blood cells make ATP?

Through glycolysis Right. All cells require ATP to run their cell membrane pumps, but mature RBCs lack mitochondria. Without mitochondria, they cannot make ATP using aerobic respiration. Since ATP cannot be stored, RBCs need to make their ATP by anaerobic processes (glycolysis).

What is the role of the sodium-potassium pumps on the cell membrane?

To move potassium against its concentration gradient To move sodium against its concentration gradient To establish the proper ionic concentrations of sodium and potassium across the cell membrane Correct! The Na+/K+ pump uses ATP to pump 3 Na+ ions out of the cell and 2 K+ ions into the cell. Because it uses energy to move the ions, it does not rely on diffusion for ion movement - meaning, it can push ions uphill against their concentration gradient. In doing this, it actually establishes the concentration gradient of these ions across the cell membrane and then re-establishes it after signals (action potentials) pass through the cell. This is an essential component to neuron function. Without the concentration gradients created and maintained by the Na+/K+ pumps, there could be no action potential.

How does calcium act during synapses?

To play a role in chemical reactions at the terminal end Right! Calcium entry into the terminal end of the neuron is caused by the presence of the AP opening voltage gated Ca++ channels. The calcium enters the terminal end and participates to activate kinases involved in synaptic vesicle release. We usually think about cAMP or IP3 acting as second messengers, but second messengers are really just molecules that participate in chain reactions (cascades) inside cells leading to cellular response. Here, calcium is playing that role. If it helps, think of the AP as the first messenger.

Which of the following make up spongy bone? - trabeculae - osteons - cortical (compact) bone - articular cartilage

Trabeculae. Right! Trabeculae are the struts of spongy bone in the epiphyses and adjacent to the medullary cavity. They are more lightweight than dense compact bone (as evidenced by their many open spaces). In the epiphyses they transmit weight to the more dense compact bone of the outer diaphyseal cortex. They remodel very rapidly in response to signals (compressive stress/hormonal fluctuations); the proximal femoral spongy bone remodels every 3-6 months but the denser compact bone may take 3-7 years to fully remodel. Osteons are the structural unit of compact bone; compact bone comprises the bulk of the outer diaphyseal cortex (cortical bone) and the part adjacent to the periosteum (outer connective tissue layer used for bone remodeling and muscle/ligament attachment). Articular cartilages (cartilage on the end of long bones) do not function for weight bearing as much as they function for friction reduction. They do not remodel in response to stress like spongy bone trabeculae do.

True or False? The sooner a person enters puberty, the sooner they will reach peak bone mass. - True - False

True. Right! As we age, bone formation at the epiphyseal plate surpasses cartilage leading to disappearance of all cartilage and replacement of this cartilage by bone. Once the bone has replaced all cartilage, the long bone cannot become longer. As bones elongate, we remodel the diaphysis and increase overall diaphyseal width. The more bones grow long, the wider their diaphysis becomes. The wider the diaphysis, the greater total bone mass. Together, the timing of the closure of the epiphyseal plate and the duration of growth between onset of puberty and closure influence peak bone mass. At the onset of puberty, cartilage and bone growth accelerate. However, cartilage death also accelerates (this effect is greater in females than males). So, the sooner you begin this progression to closure of the epiphyseal plate, the sooner you will reach peak bone mass.

True or False? In response to a neurotransmitter, depolarizating graded potentials on the cell body show a depolarization and repolarization phase, but do not show an hyperpolarization phase.

True. Right! The action potential shows depolarization, repolarization and after-hyperpolarization phases due to the opening and timing of sodium voltage gated channels and potassium voltage gated channels. The opening of the sodium voltage gated channels results in the depolarization phase as Na+ enters the cell. The repolarization and after-hyperpolarization phases occur as the K+ voltage gated channels open allowing K+ to leave the cell. During an action potential, both types of channels open in the appropriate sequence and therefore all phases are observed. BUT, in graded potentials on the neuron cell body that are caused by neurotransmitter binding, only chemically gated channels that are sensitive to the neurotransmitter open; the channels then close once the neurotransmitter is removed. Therefore, depolarization occurs as the channel opens (say, a Na+ chemically gated channel) and then repolarization as the channel closes and we return to resting conditions. Hyperpolarization can only occur if the NT opens a channel that allows different ions to move (Cl- or perhaps K+).

The presence of hyaline cartilage is required for elongation of the femur in a 10 year old child. - True - False

True. Right. The femur is a long bone that forms through endochondral bone formation (which requires hyaline cartilage). This process continues throughout childhood until the early 20's.

True or False? The epidermis protects the body from excessive water loss.

True. This is true. Although we lose some water across the skin every day (insensible perspiration), this loss is greatly lessened by the water resistant epidermis. The combination of oils and cellular layers restricts water loss significantly, especially when compared to other animals such as amphibians. The epidermis's ability to prevent excessive water loss is readily apparent when people suffer severe burns. Among the many challenges associated with loss of the protective epidermis (potential for infection, significant metabolic effort to regrow skin), water loss and the resultant electrolyte imbalance are substantial compromising factors.

On average, for human body cells, the overall intracellular fluid concentration is equal to the overall extracellular fluid concentration.

True. Yes, this is true. We are talking about if the interior is iso-osmotic with the exterior. This is true in most cases for cells of the body. If the interior concentration had a higher osmolarity than the exterior, water would rush into cells until no difference existed - this would cause swelling of the cells and disrupt their membrane protein positions or cause the cell to rupture. If the exterior had a higher osmolarity, the reverse would occur and cells would shrink. Because cells cannot restrict water movement but they can pump salt, the only way to intentionally adjust the osmolarity of the cell is with pumps. It is believed the sodium potassium pump evolved as a mechanism to regulate osmolarity. See here Links to an external site.for more on the this theory.

For a sarcomere, does the A-band contain the M-line? - Sometimes - Yes, always - No, never

Yes, always. Right! The M-line is in the middle of the thick filament. It is made of cytoskeletal proteins that anchor the middle of the thick filament & A band. The M-line (and the Z-discs) help keep the proper arrangement of the thick and thin filaments needed for proper interaction of actin and myosin. The A-band is the length of the myosin portion of the thick filament. Yes, the M-line is always in the middle of the A-band. The A-band never changes length, so the M-line should never change its position within the A.

For a sarcomere, is the M-line in the H-zone? - No, never - Sometimes - Yes, always

Yes, always. Right! The M-line is in the middle of the thick filament. It is made of cytoskeletal proteins that anchor the middle of the thick filament & A band. The M-line (and the Z-discs) help keep the proper arrangement of the thick and thin filaments needed for proper interaction of actin and myosin. The H-zone is the middle region within a sarcomere that extends from the free ends of the thin filaments on one side of the sarcomere to the free ends of the thin filaments on the other side of the sarcomere. Yes, the M-line is always in the middle of the H-zone. Should the sarcomere shorten enough, the free ends of the thin filaments would run into the M-line. When they do, the H-zone is at its narrowest and likely about to disappear.

In vitamin C deficiency you cannot synthesize collagen. Which of the following would most likely occur? - Your skeleton would become malformed. - You would not be able to replenish lost epithelial cells. - You would not be able to sweat. - Your cartilage would become avascular.

Your skeleton would become malformed. Right! The skeleton is constantly being degraded and replaced. Since the skeleton is 1/3rd collagen and 2/3rds mineral, an inability to make collagen would substantially affect the skeleton. Furthermore, proper collagen formation is required for proper bone mineral deposition. Epithelial cells do not have collagen. Sweat is mostly water and salt, and should not have collagen. Sweat glands are made of epithelial tissue, not lots of collagen like you would find in tendons/ligaments or bone. Cartilage is already avascular and actually secretes a compound that inhibits blood vessel formation. The best answer here is the one discussing skeleton formation.

What type of membrane protein is shown here? (The bottom yellow portion of each panel represents the cytosol) - NOTE THIS IS FIGURE A and WILL BE REFERENCED LATER

chemically (ligand) gated sodium channel Correct! This channel responds to the presence of Ach (acetylcholine) - a neurotransmitter. When Ach binds, the channel opens, allowing an ion to flow. The ion flows into the cell in the image - this means that the ion is more concentrated outside of the cell than in. Sodium is more concentrated outside of cells than in, and potassium is more concentrated inside cells than out. If this were a potassium channel, the potassium would flow out. Leak channels are not gated and do not respond to chemicals like Ach. Voltage gated channels respond to changes in membrane potential not Ach.

Using figure 1, compare the trace in time 2 to the trace in time 6. Trace 2 was due to ____; trace 6 was due to ____.

chemically gated channels; chemically gated channels Right! These are both graded potentials. The action potential begins at time 7 - this is when voltage gated channels open at this spot on the neuron.

Using figure 1, of the following, what contributes most to the change in transmembrane potential between 7 & 8?

decreased membrane permeability to sodium Right! At the peak (transition between 7 & 8), the sodium voltage gated channels close, decreasing membrane permeability to Na+. At the same time, membrane permeability to K+ is increasing. Chloride & calcium are not involved.

Shown below are cross-sections through a long bone at the level of the mid-diaphysis. The light gray represents new bone that is being formed at three different life stages. Secondary osteons represent where a previous osteon has been removed and then a new one deposited. Using this model, what diaphyseal cells are most active in an adult, acting to remodel and maintain bone? - periosteal cells - endosteal cells close to the marrow cavity - endosteal cells of osteons

endosteal cells of osteons. Correct! The imageshows transverse sections through the diaphysis a long bone. The remodeling seen in adults is due to secondary osteon formation and endosteal cells adjacent to the medullary (marrow) cavity. These cells include the osteoblasts and osteoclasts of the endosteum. Since endosteum is found both adjacent to the marrow cavity and in the central canals of osteons, remodeling is possible in both these places. Adult bones are not growing longer, only removing old material and redepositing in its place. However, heavily physically stressed bones are capable of increased thickness due to cells at both the endosteum adjacent to the marrow cavity and at the periosteum. More remodeling is seen in the osteons than at the medullary cavity.

The __________ are joined to one another by __________ joints. (You may want to use your lecture notes or textbook tables to help with this one.) - vertebral bodies; synarthrotic - paired flat skull bones; synchondrosis - femur and tibia; symphysis - flat hand bones (carpals); synovial

flat hand bones (carpals); synovial Right! The carpals are joined to each other by synovial joints that allow much movement to type on a keyboard or click a mouse. When two bones are joined by fibrocartilaginous material, and not also synovial membranes inside an articular (joint) capsule, the joint is classified as a symphysis joint. It is a special case of the broader category of cartilaginous joints. Symphysis joints are usually amphiarthrotic because the fibrocartilage disc has some flexibility. The femur and tibia articulate at the knee, a diarthrotic synovial hinge joint. The flat bones of the skull are joined by fibrous suture joints - they are usually immobile and classified as synarthroses. Synchondroses joints are special cases of cartilaginous joints where the joining material is hyaline cartilage - they are usually synarthrotic (immobile).If you are unsure as to what these words all mean, you can use the tables in the joint chapter and pay special attention to the terms that start with the letters "syn."

The condition Marfan syndrome is a genetic disorder that affects proper production of the extracellular fluid protein fibrillin-1. Fibrillin-1 is necessary for proper production of elastic fibers in connective tissues, though other connective tissue fibers are not affected. When elastic fibers are not properly formed, certain organs are severely affected. In extreme cases, the most affected organs include the large blood vessels near the heart which become brittle and tear open (this is very bad and can cause immediate death). Marfan syndrome is an autosomal dominant genetic disorder caused by a mutation of the FBN1 gene. Where will you find the mutated FBN1 gene?

in all somatic, nucleated cells in the body Right. This question is asking about the genome of somatic cells. All somatic cells of a person's body should have the same genome (roughly). The differences in cell specificity come from variable gene expression. Because the genetic mutation addressed above is described as an autosomal dominant, it is not acquired through mutation over time, instead present in all cells of the body. The effects of this mutation only affect certain organs because the elastic fibers are only produced by cells of those organs. Though every cell has the faulty gene, it affects only certain tissues and organs.

In the growing 10 year old, the humerus becomes longer through ____ and wider through ____. - interstitial growth and intramembranous bone formation; appositional growth at the periosteum - appositional growth and endochondral bone formation; appositional growth at the periosteum - interstitial growth and endochondral bone formation; interstitial growth at the periosteum - interstitial growth and endochondral bone formation; appositional growth at the periosteum

interstitial growth and endochondral bone formation; appositional growth at the periosteum Right! Bone elongates through interstitial growth of hyaline cartilage in the epiphyseal growth plate followed by replacement of that cartilage with bone (endochondral bone formation). At the edges of bones, appositional bone growth from the periosteum makes overall bone dimensions wider. Intramembranous bone formation does not occur in long bones.

The condition Marfan syndrome is a genetic disorder that affects proper production of the connective tissue matrix protein fibrillin-1. Fibrillin-1 is necessary for proper production of elastic fibers in connective tissues, though other connective tissue fibers are not affected. When elastic fibers are not properly formed, certain organs are severely affected. In extreme cases, the most affected organs include the large blood vessels near the heart which become brittle and tear open (this is very bad and can cause immediate death). For Marfan syndrome, the provided evidence suggests:

molecular structure is affecting organ function This passage addresses a structural component of a molecule (elastic fibers) and how it affects the body. You cannot select an option that suggests function is affecting structure - you must select that structure determines function. Therefore of the two, tissue structures are not affecting cells in this case, but a molecular structure is affecting organ function.

Using figure 1, what most likely explains why the membrane potential repolarized in time 2?

neurotransmitter was removed from the synaptic cleft Right! When NT is removed, the chemically gated channel closes, preventing further movement through this channel. Once ions cannot cross the membrane, the Na/K pumps return the membrane potential to resting levels. Unlike action potentials, no additional channels are opened to allow for repolarization, only those opened by the NT binding.

Using figure 1, what type of stimulus would trigger an additional action potential during time period 9?

persistent binding of neurotransmitter at a chemically gated Na+ channel Right! Time 9 is during the relative refractory period. Another AP is possible if the depolarizing stimulus is sufficiently large to overcome the efflux of K+. Very large stimuli can be caused by opening many chemically gated channels on the nearby cell body/dendrites or opening fewer channels, but keeping them open longer with persistent binding of NT. Additional APs are possible during the relative refractory period. NT does not bind to voltage gated or mechanically gated channels.

Sodium ions have a ____ charge and ____ a neuron when they flow down their concentration gradient.

positive; enter Correct! Sodium ions are positively charged (Na+) and are more concentrated outside the neuron due to the action of the sodium/potassium pump. When they are able to cross the cell membrane through a channel, they flow passively down their concentration gradients from where they are more concentrated to where they are less concentrated, thus entering the cell.

Potassium ions have a ____ charge and ____ a cell when they flow down their concentration gradient.

positive; exit Correct! Potassium ions are positively charged (K+) and are more concentrated inside the cell due to the action of the sodium/potassium pump. When they are able to cross the cell membrane through a channel, they flow passively down their concentration gradients from where they are more concentrated to where they are less concentrated, thus exiting the cell.