A&P Fall 2017 quizes

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

The __________ are joined to one another by __________ joints. (You may want to use your lecture notes or textbook tables to help with this one.)

; 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).

Which can pick up the heavier load? (Assume otherwise equal joint architecture.)

A short muscle with a large physiological cross sectional area. Physiological cross sectional area (PCSA) determines the maximal force production in a muscle. More sarcomeres pulling in parallel generate more tension than more sarcomeres pulling in series (fiber length). The larger the PCSA, the more peak force a muscle can generate and the heavier the load that can be lifted.

Why is the concentration of calcium so high in the sarcoplasmic reticulum during rest?

Because ATP dependent pumps actively move it there from the sarcoplasm 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.

At rest, why is myosin in the high energy state? (Rest means no AP on the sarcolemma.)

Because the energy in ATP was transferred to the myosin after the ATP caused crossbridge detachment.

Why is acetylcholine (Ach) used at the junction between neurons and muscle cells?

Because the neuron's action potential cannot cross the synaptic cleft

After a fracture, what is the correct sequence of repair?

Blood clot, cartilage patch, bony patch, bone remodel

What would happen if your cell membranes did not contain sodium-potassium pumps?

Both of the above would happen if your cell membranes did not contain sodium-potassium pumps. Right! The sodium-potassium pump is on every cell membrane - including neurons and muscle cells. The pumps are not in one spot on the cell membrane but all along the membrane. They pump 3 sodium ions out of the cell, while pumping 2 potassium ions into the cell. When they are active (which is always), they create a concentration gradient for sodium and potassium across the cell membrane. This separation of ions across the cell membrane creates a measurable voltage (the membrane potential). Even at rest (the cells are neither sending nor receiving a signal), these pumps are working. Due to their actions, the membrane has a potential at rest. When neurons and muscles "send signals" they change the membrane potential by opening gated sodium and potassium channels, allowing rapid ion movement across the cell membrane. As these ions move, the membrane potential changes. If the pumps did not establish concentration gradients for these ions, the cells could not have a resting membrane potential or generate signals using rapid, passive sodium & potassium movement through gated channels.

Keratin is an intracellular protein. How is it made?

By a free ribosome Free ribosomes synthesize proteins for intracellular purposes. Fixed ribosomes on the rough ER synthesize proteins as well, but those are exported from the cell to be used on the cell membrane or elsewhere in the body. The nucleus contains the genetic code in the form of DNA to determine the structure of proteins. The smooth ER makes carbohydrates and lipids.

During a twitch in a skeletal muscle fiber, what is happening in the latent period?

Calcium is flowing through mechanically gated channels

What type of channels in the motor end plate bind Ach (acetylcholine, a neurotransmitter)?

Chemically (ligand) gated sodium channels The motor end plate is the region on the muscle cell membrane that binds neurotransmitter. Chemically (ligand) gated channels open when a chemical binds to the binding site (receptor) on the channel. The channel that opens in response to Ach on the motor end plate is a sodium channel and when it opens, sodium moves down its own concentration gradient into the muscle cell. This sodium entry will change the membrane potential of the motor end plate (moving it closer to 0 mV). As the sodium ions enter the muscle cell, they spread out to the nearby sarcolemma, also changing this region's membrane potential. When the nearby sarcolemma membrane potential changes, the voltage gated channels embedded in it will open.The opening of specific voltage gated channels is called an action potential. Action potentials can only occur on cells that have the right types and amounts of voltage gated channels. Voltage gated channels open when the membrane voltage (potential) near the channel changes. Ach is not directly involved. Leak channels are always open. Ach is not involved. The sodium potassium pump moves sodium and potassium across the cell membrane; Ach is not involved.

Which tissue type is charaterized by cells scattered throughout an extracellular matrix of proteins?

Connective. Connective tissue is made up of relatively few cells (as opposed to epithelial and muscle tissue) scattered throughout an extracellular matrix. Many seemingly disparate tissues in the body are connective: bone, blood, and dense connective tissue (tendons) to name a few. You may have noticed that these details about tissue types are not included in the slides I posted for you. Remember, posted slides are only an outline. It is up to you to complete them by listening in lecture and supplementing the outline.

Which of the following will least likely reduce movement of the upper limb?

Decreased elasticity of the sacroiliac ligament The sacroiliac joint is the the articulation between the pelvis and sacrum - the ligaments holding it include the sacroiliac ligaments.

Which of the following will increase force production in a skeletal muscle?

Decreasing the time between successive neural stimulations Decreasing the time between successive neural stimuli to a muscle means that you are stimulating the muscle more frequently. Increasing stimulus frequency increases force production in a muscle fiber or whole muscle because it allows more calcium to persist in the sarcoplasm. More calcium binds to more troponin leading to more availability of actin for crossbridge formation. Increasing the activity of acetylcholinesterase or the pumps on the SR will decrease force. AchE will remove Ach from the motor end plate, ending APs on the sarcolemma and thus ending contraction. If the SR pumps are more active, they will remove more calcium from the muscle cell sarcoplasm and end contraction. Increasing the latent period length will make for less frequent contractions. Changing the ratio between muscle fibers and motor neurons does not affect force production.

To be activated, skeletal muscle fibers must receive neurotransmitter from neurons. What structure must neurons penetrate to activate the myofiber

Endomysium

What structure must neurons penetrate to activate the myofiber?

Endomysium 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.

What type of fluid is found in the transverse tubules (t-tubules)?

Extracellular fluid (ECF) 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? Endochondral bone formation stops at birth.

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.

Flagella are used to move fluids across the surface of the cell

False indeed. Cilia are used to move fluids across the surface of their cells. Cells with cilia are anchored in place but may need to propel the fluid around them. Flagella allow a cell to move through its liquid environment. Sperm are the only flagellated cells in the human body.

Meiosis produces gametes that are genetically identical to the parent cell and are used in reproduction.

False. Although it is true that meiosis produces sex cells for reproduction, the gametes that are produced are not genetically identical to the parent cells. Instead, they contain half the DNA of the parent cell.

Bones like the femur are only composed of connective tissue.

False. Bones are organs, and like all organs, bones are composed of multiple tissue types. While much of bone is connective tissue, blood vessels in bones contain smooth muscle and epithelial tissue. Sensory neurons also receive signals from bone.

Small, fat-soluble molecules require transport proteins to cross the cell membrane

False. Generally speaking, small uncharged molecules, gasses and fat-soluble molecules can pass through the cell membrane without a channel, carrier or transport protein, as long as they are traveling DOWN their concentration gradient. Ions and larger water soluble molecules require protein channels, carriers or transport proteins to cross the membrane.

During transcription, the small and large ribosomal subunits combine to read the mRNA strand and synthesize an polypeptide (amino acid chain).

False. Translation, not transcription, is the process in which the small and large ribosomal subunits combine to read the mRNA strand and synthesize an polypeptide (amino acid chain). During transcription, an enzyme copies a gene from the DNA on an mRNA molecule.

All organisms must breathe oxygen in order to survive.

False. While all organisms metabolize to gain energy, not all organisms use oxygen. Even in the human body, there are anaerobic processes which allow us to harvest energy without using oxygen.

Which organ is best described as one in which there are some cells, there is more ground substance than extracellular fibers, and the ground substance is solid at maturity?

Femur The four primary tissue types are epithelial, connective, muscle and neural. Only connective tissues are characterized using the terms ground substance - and of this list, bone (the femur, thigh bone) is the only 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).

The enzyme pepsin is responsible for catalyzing the digestion of food proteins in the stomach. Which of the following conclusions would be most logical?

Food proteins are unable to cross the membranes of digestive cells unless digested. Much of what we consume, include protein, is too large to be absorbed into our digestive cells. We reply on digestive enzymes to catalyze the digestion of these foods so that we can absorb their components. Enzymes are substrate specific; that means their active site is formed to fit only one particular type of substrate and that is the only reaction they can catalyze. Enzymes are not used up or destroyed by the reactions that they catalyze, but can be use again and again unless they become denatured. Denaturing occurs when enzymes are exposed to pH or temperature out of their optimal range. An enzyme that functions in the very acidic environment of the stomach would likely be denatured in the neutral small intestine.

Where in a sarcomere do you find the thick filament, but not the thin filament?

H-zone

Where in a sarcomere do you find titin and tropomyosin, but not myosin?

I-band Right! The I-band, or the lIght band, is the region of the sarcomere that contains the Z-disc and the structures directly connected to it - the thin filament, which contains actin, tropomyosin and troponin, and titin. Myosin is the protein that makes up the thick filament. The H-zone is the region of the sarcomere that only contains myosin. The M-line, at the center of the H-zone, cross links the thick filament. The zone of overlap is the region of the sarcomere where the actin and myosin are able to interact because they physically overlap with one another.

Where do you find the cells that act to remodel or maintain bone?

In all of the listed structures 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.

Which of the following will NOT likely reduce movement of the upper limb?

Increased tightness of the acetabular labrum The femoroacetabular joint is the the articulation between the pelvis and femur (it is the hip). The fibrocartilaginous labrum extends from the acetabulum (socket) and increases the tightness of this joint. The tighter the joint, the less the joint moves. The pectoral girdle are the bones that attach the upper limb to the axial skeleton - they include the clavicle and the scapula. It forms the following joints: the sternoclavicular, the acromioclavicular and the physiological scapulothoracic. Largely, anything that affects mobility of the pectoral girdle will affect range of motion of the upper limb. The upper limb relies on movements of the scapula for increased range of motion - since the sternoclavicular joint is the only bony connection between the upper limb and the axial skeleton, fusing the sternoclavicular joint would reduce the clavicular movement and the attached scapular movement; then, the upper limb range of motion would be reduced by some 30-50 degrees (degrees vary for direction of movement). Disruption of the acromioclavicular joint often reduces range of motion, but may not in all people (interestingly). Arthritis (loss of articular cartilage) in the glenohumeral joint will cause pain and inflammation of the junction of the humerus in the glenoid cavity (fossa) and reduce movements of the shoulder.

Oxygen is essential for cellular respiration and therefore must cross the cell membrane. Which of the following would increase O2 transport into a cell?

Increasing surface area of the cell's membrane

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 epithelial tissue 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).

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, 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.

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 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.

What would happen if you somehow increased the amount of acetylcholinesterase (or its activity) in the synaptic cleft?

Muscle contractions would be shorter or may not happen

Acetylcholinesterase breaks down Ach in the synaptic cleft. What would happen if you somehow increased the amount of acetylcholinesterase (or its activity) in the synaptic cleft?

Muscle contractions would be shorter or may not happen Acetylcholinesterase (AchE) is an enzyme that breaks down Ach in the synaptic cleft. When it is active, it removes Ach from the ligand gated channels and ends the entry of sodium into the muscle cell. This ends the opening of voltage gated channels which ends the AP on the sarcolemma. Without an AP, there is no muscle contraction. If you somehow have too much AchE, it would break down the Ach faster and stop the generation of APs on the muscle. This effect would be to either have briefer muscle contractions, or if there was so much AchE, no muscle contractions because of very few APs or none, respectively. In some conditions, muscles do not respond well to neural stimuli. The treatment for these diseases can include a drug that blocks the action of AchE, thereby allowing longer interaction between Ach and the channels and therefore more APs and more muscle contraction.

Which is true?

Myofilaments are protiens

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). 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 rate (the rate at which it pumps blood) varies depending on your degree of physical activity or neural/hormonal activity. 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. 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.

In anatomy, collateral means accessory, subordinate, secondary, serving to support or reinforce. Knowing this, where would you expect to find the tibial collateral ligament?

On the medial aspect of the knee Collateral ligaments are groupings of ligaments that function together to support joints. Of the choices listed here, you can eliminate anything having to do with the elbow. Ligaments around the elbow joint should be named ulnar or radial because they are the bones in that area. This leaves us with the knee. In the leg, the fibula is lateral and the tibia is medial. As such, the tibial collateral ligament is found on the medial aspect of the knee. The fibular collateral ligament is on the lateral aspect. This question was really asking you anatomy of the upper and lower limb, but also forced you to apply your understanding of general joint anatomy.

Tendons have many collagen fibers. Which of the following best describes where these fibers are located?

Outside the fibroblasts, in the extracellular matrix 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.

According to this figure, what is the primary hormone regulating blood calcium?

Parathyroid hormone (PTH) The parathyroid glands are small glands attached on the posterior of the thyroid gland. They secrete parathyroid hormone 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.

What organelle of skeletal muscle cells stores calcium used in muscle contaction?

SR The sarcoplasmic reticulum (SR) is a special smooth endoplasmic reticulum (ER). Since smooth ER can be used for storage (as well as fat synthesis or carbohydrate synthesis), here it stores calcium. When a signal for contraction arrives, the calcium is released from storage and interacts with the contractile elements to produce muscle force. Myofibrils are the contractile elements of skeletal muscle - they contain actin and myosin. The SR wrap around the myofibrils (like red licorice over spaghetti noodles). Mitochondria are used for ATP production. The sarcolemma is the cell membrane of the skeletal muscle cell.

Cancers are more common in tissues with high rates of mitotic division. Based on this information, which of the following tissues would be most likely to deveolp cancerous tumors.

Skin epithelium

Cancers are more common in tissues with high rates of mitotic division. Based on this information, which of the following tissues would be most likely to deveolp cancerous tumors.

Skin epithelium Our skin epithelium is subject to a lot of external abrasion and must replace itself frequently. Consequently, skin epithelial cells have high rates of mitotic division, which can contribute to a higher likelihood of errors in the control mechanism for cell division and result in cancer. Frequent, direct exposure to UV radiation also contributes to higher rates of cancer in skin epithelial tissues. Neural, skeletal muscle and cardiac muscle tissues are composed of cells with much lower rates of mitotic division. Though they can develop tumors, they are less common

Sodium (Na+) is more concentrated outside of cells than inside cells. What would happen if the cell membrane permeability to sodium suddenly changed?

Sodium rushes into the cell passively (net inward movement) Membrane permeability to an ion can change when a gated ion channel opens and the ion can then cross the cell membrane. Sodium ions are more concentrated outside of all cells because the sodium-potassium pump constantly moves 3 sodium ions out of the cell while moving 2 potassium ions into the cell. This activity uses ATP. Because sodium ions are so concentrated outside the cells compared to the inside, when allowed through a channel, the sodium will rush passively down its concentration gradient and enter the cell (passively means that no ATP must be used by the cell to move the ion). Sodium will not flow passively out of the cell because nature does not favor more sodium being located outside the cells. Nature favors equilibrium - an equal amount of sodium inside and outside. Because there is so much sodium outside the cell and so little inside, passive movement of sodium permits only net movement of sodium into the cell.

Sodium is more concentrated outside of cells than inside cells. What would happen if the cell membrane permeability to sodium suddenly changed?

Sodium rushes into the cell passively (net inward movement). Membrane permeability to an ion can change when a gated ion channel opens and the ion can then cross the cell membrane. Sodium ions are more concentrated outside of all cells because the sodium-potassium pump constantly moves 3 sodium ions out of the cell while moving 2 potassium ions into the cell. This activity uses ATP. Because sodium ions are so concentrated outside the cells compared to the inside, when allowed though a channel, the sodium will rush passively down its concentration gradient and enter the cell (passively means that no ATP must be used by the cell to move the ion). Sodium will not flow passively out of the cell because nature does not favor more sodium being located outside the cells. Nature favors equilibrium - an equal amount of sodium inside and outside. Because there is so much sodium outside the cell and so little inside, passive movement of sodium permits only net movement of sodium into the cell. Something will happen when the membrane permeability changes, but that something will be whatever nature favors.

What is the difference between spongy and compact bone?

Spongy bone and compact bone are microscopically arranged differently 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.

Which will allow you to lift a heavier load?

Stimulating a muscle more frequently. Muscle force is related to the number of cross-bridge cycles that can occur. To lift a heavier load, you muscle must generate more force. If you recruit fewer motor units, less fibers are active and therefore less cross-bridges can form. If you stimulate the muscle more frequently, you will release more Ca from the SR and therefore the binding site on actin is exposed more and more cross-bridges can form. If you contract the muscle at a very long length, the actins are pulled to the ends of the myosins and fewer cross-bridges can form.

Which of the following would most likely affect your ability to maintain proper blood calcium?

Surgical removal of parathyroid glands, leaving thyroid gland in body The parathyroid glands are small glands attached on the posterior of the thyroid gland. They secrete parathyroid hormone 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. While the thyroid gland does secrete a hormone called calcitonin, it is not important in regulating adult blood calcium. Removal of the parathyroid glands would be most devastating to blood calcium balance for these reasons. The answer involving vitamin D is wrong because that statement suggests that bone cells respond to vitamin D - the GI tract responds to its activated form (calcitriol) to absorb calcium ions from the gut.

Which of the following is a fibrocartilage cartilaginous joint?

Symphysis Fibrocartilage has a bit of give to it, so symphyses are amphiarthrotic. You find this joint type in the vertebral column and between pubic bones.

The acromioclavicular joint is an amphiarthrotic syndesmosis.

The AC joint is not amphiarthrotic. It is diarthrotic and a synovial joint (specifically a gliding joint). Though we tend to think of the movement of the arm coming from the glenohumeral joint, the AC and sternoclavicular joints are critical to allow the full range of motion of the arm. There are a lot of joint classifications to remember, and the words sound similar (e.g. syndesmosis, synarthrosis, synchondrosis). Be sure to spend some time working through the joint vocabulary, and be familiar with examples of the different joint types.

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 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.

Suppose you are a cytologist and you are examining an 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. 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. Cytoskeletal elements help give support and structure to cells. In particular, 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.

Apocrine sweat glands, like those in the armpit, produce a watery secretion rich with pheromone oils. Which of the following best describes the cells of these glands that export these secretions?

The cells contain smooth ER and golgi apparatus

In which of the following would you expect to find osteons?

The diaphyseal cortex of the humerus

In which of the following would you expect to find osteons?

The diaphyseal cortex of the humerus Osteons are the structural unit of compact bone. They make up the thick walls of long bone diaphyses and the most superficial compact bone (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 vertebral column (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.

What is its role of endosteum in bone?

The endosteum can add or remove bone from the inside of bones, remodeling them. 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.

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 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.

Compare the hip and shoulder. Which joint has more contact with its socket?

The hip (femoracetabular) has more contact between bony elements than the shoulder (glenohumeral). The acetabulum is deeper than the glenoid cavity (fossa) and there is more interaction between the elements. This confers more stability to this joint compared to those with less bony contact.

In an infant's humerus, what happens if the rate of hyaline cartilage death is faster than the rate of interstitial growth?

The humerus would become too short at full maturity. 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?

The joint between the pubes and the joint between the bodies of adjacent vertebrae 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 joints between ribs 2-7 and the sternum 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).

What is the most inferior articulation between the axial and appendicular skeletons?

The joint between the sacrum and ilium

Which are synovial joints?

The joints between true ribs (with the exception of the first) and the sternum. The joints between true ribs (with the exception of the first) and the sternum are synovial (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 gomphoses, the joint between the distal tibia/fibula and the interosseous membranes are all fibrous. The radioulnar joint is synovial pivot.

Bisphosphonate medications (like Boniva) result in osteoclast death. Such medications have been prescribed to those at risk of osteoporosis, but after long term use, some people developed mid-shaft femoral fractures. Why?

The medication decreased bone remodeling and microfractures did not heal. Bone must be remodeled through the combined activity of osteoblasts and osteoclasts. Osteoclasts destroy old bone, but in doing so, give an opportunity for osteoblasts to deposit new healthy bone. When osteoclasts cannot destroy the old bone, the old bone remains, allowing microcracks that develop from long term activity to build up. These areas are not remodeled and replaced as often as they need to be. It has also now been realized that osteoclast activity helps determine osteoblast activity. When new spaces are scoured by osteoclasts, osteoblasts then come along and fill in the spaces. Bone that has not been frequently remodeled becomes brittle and fractures more readily, but in odd places (like diaphyseal fractures) where stress damage has accumulated. Osteoporosis results when osteoclast activity is greater than osteoblast activity, making bone weak. Although osteoporosis does result in more fractures of bone due to low bone density/mineralization, the type of fractures are usually compression fractures of the vertebral column or other places of higher typical spongy bone density. The bisphophonates worked to maintain spongy bone density and limit typical osteoporotic fractures, but instead allowed frequently cortical bone microfractures to build up by limiting osteon remodeling.

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 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?

In this image, which of the following could be described as most inferior?

The plantar surface of the foot

When you swim in a pool, your body gains water. When you swim in the ocean you lose water. What most likely explains these observations?

The pool water is less salty than the inside of your body (and cells); the ocean water is saltier than the inside of your body (and cells) 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.

What happens when parathyroid glands become hyperactive and secrete too much of their hormone

The skeleton becomes weak PTH stimulates osteoclasts which degrade the skeleton. PTH secreting tumors result in osteoporotic skeletons and overly high blood calcium (because the calcium is released from skeletal storage). All the other results might occur if calcitonin were overly secreted (perhaps, but not always because calcitonin is often unimportant in the adult skeleton).

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 stable the joint

What is the relationship between the tightness of the ligaments reinforcing joints and that joint's range of motion?

The tighter the ligaments, the less range of motion

What characteristic unites all connective tissue?

They all come from a common embryonic tissue (mesenchyme)

What characteristic unites all connective tissue?

They all come from a common embryonic tissue (mesenchyme) 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 - 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.

Why do sodium ions enter a cell when gated sodium channels open?

They move down their concentration gradient passively, by diffusion.

Is bone mass homeostatically regulated?

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? You can achieve full range of upper limb motion at the shoulder (flexion, extension, abduction and adduction) only through movements of the glenohumeral joint.

This is false. Scapular movements extend the shoulder range of motion beyond the ranges permitted by the glenohumeral joint alone. For examle, during shoulder abduction, above about horizontal, the clavicle begins to elevate at the sternoclavicular joint and the scapula rotates at the physiological scapulothoracic joint to permit further abduction. Without the combined movements of these joints together, upper limb total mobility is greatly reduced.

Which of the following make up spongy bone

Trabeculae 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 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 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.

Which of the following is a protein that acts to permit the action of another protein?

Troponin Troponin and tropomyosin are regulatory proteins - they allow or disallow the interaction of actin and myosin during muscle activation or inactivation. When calcium is released from the sarcoplasmic reticulum during muscle activation, it then binds to troponin. Activated troponin moves tropomyosin away from the active site on myosin. Once tropomyosin is removed, actin and myosin can interact, producing tension (force).

How do ions move from low concentration to high concentration?(Against a concentration gradient)

Using cellular energy (ATP) Because nature favors equilibrium, ions that are clustered together will bounce off of each other very frequently and move away until they are evenly separated from one another. To then move ions to where they don't really want to be (not energetically favorable), you must use ATP. I think of this like pumping water from a well - gravity pulls water to the bottom and to overcome gravity, you must use energy to bring the water up. ATP dependent pumps are used by cells to move ions against a concentration gradient (from low to high; also called uphill or against a concentration gradient).

In which of the following conditions would you most reasonably expect to generate the most tension in a single muscle fiber? Assume otherwise equal conditions.

When a motor neuron generates a high frequency of action potentials. (greater than 80/s). Tension is related to the number of crossbridges being formed. The more crossbridges, the more tension the muscle/fiber develops. When the motor neuron generates a high frequency of action potentials more Ach is released to the muscle cell generating a high frequency of action potentials on the muscle cell. At this high AP frequency on the muscle cell (80-100 stimuli/s), the muscle cell is stimulated to complete tetanus. The most muscle force of a fiber is generated during complete tetanus because the most calcium is available to the troponin and therefore the actin/myosin binding site remains open for longer periods of time and the most crossbridges can form and cycle. The role of acetylcholinesterase is to break down Ach in the synaptic cleft. When it is maximally active, the Ach is removed from the cleft, ending contraction in the muscle. At the described long length, the actin and myosin are pulled past one another and cannot form crossbridges. No crossbridges, no tension. Twitch is a brief contraction and relaxation of the muscle fiber. It generates a very low amount of tension because crossbridges form only briefly.

When you are lying prone on the beach getting a good tan while studying your anatomy textbook, which of the following anatomical structures is considered anterior?

Your navel (umbilicus, belly button) No matter what your actual position, anatomical position refers to the individual standing erect, facing forward, feet on the ground, palms open with thumbs turned outward. Regardless of the actual position that this question describes, all anatomical language and relationships are in reference to anatomical position. In anatomical position, the umbilicus is anterior, the calf, elbow point and dorsal thigh are all posterior.

In vitamin C deficiency you cannot synthesize collagen. Which of the following would most likely occur?

Your skeleton would become malformed. 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.

As a contracting muscles shortens the _____ lengthens.

Zone of overlap

Which of the following will affect how heavy a load some joint can move?

all of the above The relative position of muscle & bones determines the mechanical advantage/disadvantage of a joint. If a mechanical advantage, the joint can move a heavy load with relatively little muscle force generation. If a mechanical disadvantage, the joint can move a load a relatively great distance at a good speed. Fiber pennation angle contributes to PCSA and thus total force production of a muscle. However, pennation angle lessens how much a muscle will shorten and therefore lessens range of motion through a joint. Overall, joint mechanics reflect the architecture in terms of position of bones and muscles as well as the intrinsic properties of the muscle such as pennation angle, PCSA and fiber type.

In extreme circumstance, contractions that recruit _____ motor units in a muscle to _____ are the most powerful, but they cannot be sustained for long periods of time.

all; complete tetanus The greatest muscle contraction (whole muscle) occurs when all motor units in the muscle are activated. If only some are activated, submaximal force is achieved. Each muscle fiber if stimulated to complete tetanus will generate its maximal tension. Submaximal tension is generated when a single fiber twitches or is stimulated so that partial relaxation occurs before the next stimulus arrives (incomplete tetanus). Therefore if all motor units are activated to complete tetanus, the greatest possible whole muscle contraction occurs. Complete tetanic contractions require ATP to be provided at a very high rate to allow continued crossbridge cycling. Because these contractions require such a high ATP demand/unit time, sufficient oxygen cannot be delivered by the cardiovascular and respiratory systems to generate all ATP aerobically (using the mitochondria). Therefore oxygen is unavailable for all ATP generation and most ATP must be generated anaerobically (by a process called glycolysis - this takes place in the cytoplasm). Without enough oxygen, most of the end products of glycolysis (pyruvic acid) are converted to lactic acid which diffuses into the blood. This lactic acid acidifies the blood causing cells (including the brain) to not function properly. As such, contraction ends partially due to signals from the brain terminating the contraction. Therefore, complete tetanic contractions of whole muscles cannot be sustained for long periods of time.

Endochondral ossification:

begins when osteoblasts are delivered by blood vessels. Right! Endochondral bone formation requires blood vessels to form and deliver osteoblasts to the site of ossification. A hyaline cartilage (not fibrocartilage) protobone exisits. The chondrocytes in that proto bone cannot become osteoblast; the osteoblasts must be brought in. These first osteoblasts begin to form the bony collar, which is the periosteum. As the bone collar grows, the cartilage within it begins to dye. Bone continues to grow from the primary ossification center in the diaphysis until maturity. In intramembranous bone formation, mesenchymal cells in the area differentiate to form osteoprogenitor cells and eventually osteoblasts.

When a motor neuron and the skeletal muscle cell it innervates are at rest:

calcium is actively transported into the SR

During sustained skeletal muscle contractions, crossbridges are:

constantly breaking and reforming asynchronously.

Cells:

have phospholipid membranes which regulate the passage of molecule into their cytosol. Some cells, including the mature red blood cell, do not have nuclei. DNA must be organized as chromatin to allow transcription to occur, so most cells (even rapidly dividing skin cells) spend more time with their DNA organized as chromatin than chromosomes. Cells divide by mitosis to replace dead or damaged cells.

You find a tissue that has the following characteristics: avascular cells contain nuclei, rough ER, golgi apparatuses and mitochondria cells are widely spaced from one another Where did this sample likely come from?

intervertebral disc 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.

During formation of the flat portions of the frontal bone, ______ differentiate to become _______.

mesenchymal cells; osteoblasts 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.

During skeletal muscle activation, each myosin requires ____ ATP per cross bridge cycle, and myosin heads cycle ____.

one; as often as possible

Which is the lowest level of organization? (lowest of the options)

oxygen

During a sustained submaximal whole muscle contraction (like muscle activation that keeps your head upright throughout the day), what is happening in your neck muscles?

some motor units are activated to incomplete tetanus while others are resting Many sustained submaximal contractions involve activating only some motor units while others are resting. Contractions of whole muscles that are maintained over many hours usually are due to the activation of some motor units to incomplete tetanus while others are resting. When some motor units are activated, they are carefully controlled by your nervous system to activate out of sequence with other motor units so that smooth, sustained contractions result. If your muscle needs more tension to develop, it will activate more motor units also to incomplete tetanus. Complete tetanus is not usually generated in motor units unless maximal force is needed from the muscle and then, all motor units are activated at once to complete tetanus. If all motor units were twitching synchronously tension would rise and then fall very rapidly in the muscle. The force produced would be submaximal, but the action of the whole muscle would not be very smooth and would not be sustained longer than the twitch duration, probably something like 200 ms.

Comparing the glenohumeral and femoroacetabular joints:

the femoroacetabular joint has a larger labrum.

In a muscle cell:

there are many nuclei and the sarcoplasm contains abundant mitochondria

_____ are useful in the skeleton because they remodel most readily in response to stress and efficiently transmit forces while remaining lightweight.

trabeculae 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 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 diaphyseal cortex (cortical bone) and the part adjacent to the periosteum. 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.

I think if a joint is more stable, it will....

will be less likely to dislocate than a similar type, but less stable joint.