Unit 2 Book Questions

Muscle tone is

the result of a small amount of involuntary activation of motor units by the nervous system

The dark band containing the entire length of the thick filament

A band

Mr. Nasheed has cerebral palsy and suffers severe skeletal muscle spasms as a result of his condition. He is prescribed the drug dantrolene, which prevents the release of Ca2+ from the SR. Explain how this will treat his muscle spasms.

Blocking the release of calcium ions from the SR will prevent calcium ions from flooding the cytosol and binding to troponin. This will prevent actin and myosin from binding and the initiation of contraction.

Which of the following is not a function of articulations?

Blood cell formation

Major excitatory neurotransmitter in the brain

Glutamate

Which of the following is not likely to result from endurance training alone?

Hypertrophy of the muscle fibers

Predict how the characteristics of a person's bones would change if compact bone were located on the inside and spongy bone on the outside.

If the spongy bone were on the outside, the thin trabeculae would be subjected to more mechanical trauma than usual, which would damage their structure. In addition, the bone marrow housed within the trabeculae could also sustain damage without the outer shell of compact bone to protect it.

The band of proteins in the middle of the H zone

M line

When a pathologist performs an autopsy on a person who died of a brain injury, explain why he or she typically finds large numbers of microglia in the brain.

Microglia are phagocytes that ingest dead or damaged cells in the brain, including neurons and other neuroglia. A brain injury results in damaged cells, and as a result, more microglia will be present.

Phagocytic cells of the CNS

Microglial cells

Which of the following statements best describes saltatory conduction?

Only the nodes of Ranvier must generate action potentials.

Which of the following energy sources would provide the majority of the ATP for a person running a 26-mile marathon?

Oxidative catabolism

The functional unit of contraction

Sarcomere

What is the difference between a primary and secondary ossification center in a long bone?

The primary ossification center is generally in the diaphysis of a long bone, whereas the secondary ossification centers are generally in the epiphyses

The primary mineral in the inorganic matrix is hydroxyapatite

Ture

Which of the following types of muscle fibers have low myosin ATPase activity and are classified as slow-twitch?

Type I fibers

The boundary between sarcomeres

Z-disc

Bone deposition is triggered by tension placed on the bone

True

Identify each of the following joints as synovial, fibrous, or cartilaginous. a. Pubic symphysis b. Elbow joint c. Epiphyseal plate d. Frontal suture e. Gomphosis

a. cartilaginous b. synovial c. cartilaginous d. fibrous e. fibrous

Neurotransmitter released at the neuromuscular junction

Acetylcholine

Anchor neurons and blood vessels, maintain extracellular environment around neurons, assist in repair of damaged brain tissue

Astrocytes

Multiaxial joint in which the spherical articular surface of one bone fits into a cup or socket of another bone

Ball-and-socket joint

Long bone

Bone that is longer than it is wide

Epiphysis

End of a long bone

Major inhibitory neurotransmitter in the brain

GABA

The middle region of the A band containing only thick filaments

H zone

xplain what would happen if depolarization of the trigger zone led to a negative feedback loop instead of a positive one.

If depolarization triggered a negative feedback loop, the initial depolarization to threshold would not lead to further depolarization. Instead, it would lead to repolarization and the cell would return to its resting membrane potential.

Which of the following best describes single-unit smooth muscle tissue?

It contains gap junctions that couple the fibers electrically

Periosteum

Membrane surrounding the bone

Catecholamine involved in the autonomic nervous system

Norepinephrine

Create the myelin sheath in the CNS

Oligodendrocytes

Which of the following is not a function of the skeletal system?

Primary storage site in the body for the minerals sodium and potassium

Diaphysis

Shaft of a long bone

Neuropeptide involved in transmission of pain

Substance P

Which of the following statements accurately describes the role of ATP in a muscle contraction?

ATP breaks the actin/myosin attachment and "cocks" the myosin head

Paola is a 3-year-old girl with a disease that reduces the ability of her mitochondria to generate ATP. Explain the specific effects of this disease on the ability of Paola's muscles to function properly. What other tissues and organs are likely to be especially affected by her disease, and why?

ATP is required to fuel multiple aspects of muscle contraction, including cocking of the myosin head, running the pumps in the SR, and running the Na+/K+ pumps in the sarcolemma. A decrease in ATP production would therefore interfere with all aspects of muscle tissue function. Other organs and tissues with high metabolic rates would also be affected, including the kidneys, the heart, the brain, and the liver.

Which of the following factors is/are responsible for muscular fatigue?

Accumulation of chemicals, including calcium and phosphate ions Decreased availability of oxygen Psychological and environmental factors Depletion of key metabolic fuels, such as creatine phosphate

Order the following events of excitation and excitation-contraction coupling

Acetylcholine binds to receptors on the motor end plate, and ligand-gated ion channels open The motor end plate generates an end-plate potential The action potential propagates through the sarcolemma and dives deeply into the cell along the T-tubules The action potential spreads along the T-tubules, SR Ca2+ channels are pulled open, and Ca2+ flood the cytosol Ca2+ bind troponin, which allows tropomyosin to move away from the actin active site, initiating a contraction cycle

Albert accidentally ingests the poison tetrodotoxin from the pufferfish, which you know blocks voltage-gated Na+ channels. Predict the symptoms Albert will experience from this poisoning.

Albert's nervous system will partially or completely shut down, as action potentials will be unable to propagate along his axons. This will result in paralysis, loss of autonomic functions, and mental impairment. The severity of the symptoms will depend on the amount of poison he ingested, but could include a decrease in all functions of the brain and nervous system. Death results from moderate to severe poisoning.

Predict the appearance of the muscle fibers of an athlete who trains to run marathons.

An athlete who runs marathons likely undergoes endurance training. This individual probably has a higher number of type I fibers, and the training would likely increase the number of mitochondria, the amount of oxidative enzymes, and the blood flow. Each of these adaptations would make the athlete's muscle fibers more resistant to fatigue.

Injuries may damage the nerves of any motor or sensory division of the PNS. In which PNS subdivision would a nerve injury be most threatening to survival? Explain.

An injury to the visceral motor division would likely be the most threatening to survival. This division innervates the viscera, including the heart, the smooth muscle of hollow organs, and the glands. Damage to this division would therefore produce disturbances in variables such as heart rate and blood pressure, which could prove fatal.

The poison ouabain (wah-BAY-in), or arrow poison, blocks the Na+/K+ pump. What effect would this poison have on the sodium and potassium ion gradients, and so on the action potentials of a muscle fiber?

Blocking the Na+/K+ pump would disrupt the resting membrane potential and eventually deplete the Na+ and K+ gradients. This would diminish the amount of Na+ in the extracellular fluid available for depolarization and the amount of K+ in the cytosol available for repolarization. Eventually, action potentials would cease.

Short bone

Bone that is about as wide as it is long

Flat bone

Bone that is broad and thin

A new drug opens ligand-gated calcium ion channels in the membrane of the postsynaptic neuron. Would this produce an EPSP or an IPSP? Would this make an action potential more or less likely to occur? Why?

Calcium ions are more concentrated in the extracellular fluid, so when calcium ion channels are opened, calcium ions follow their gradient and flow into the cytosol of the neuron. The influx of positive charges produces an EPSP. Repeated EPSPs make an action potential more likely to occur.

Medullary cavity

Canal running down the center of the diaphysis

Explain why cardiac muscle cells and some smooth muscle cells will continue to contract even when their nerve supply has been removed.

Cardiac muscle cells and some smooth muscle cells are stimulated by pacemaker cells that stimulate the cells to have action potentials. Such cells do not require stimulation from an external nerve supply.

Which bones form via intramembranous ossification?

Certain flat bones

Biaxial joint in which the oval, convex articulating surface of one bone fits into the shallow depression of another bone

Condylar joint

Would extra creatine phosphate likely enhance performance of activities lasting several minutes to an hour? Explain.

Creatine phosphate, even when provided in excess, yields only enough energy to fuel activities lasting a few seconds. Activities lasting longer than this will be fueled by glycolytic and oxidative catabolism, and extra creatine phosphate will be of no benefit.

The poison curare (kyoo-RAH-ray) blocks the binding of acetylcholine to its receptors at the neuromuscular junction. What effects would you predict from such a poison? Can you think of any useful applications for it? Why might an overdose of it be lethal?

Curare would prevent acetylcholine from binding to the motor end plate and initiating contraction, effectively paralyzing the recipient. This could be useful in the treatment of muscle spasms and in cases in which a patient must be paralyzed, such as during surgery. An overdose would be lethal because it would paralyze the respiratory muscles and prevent breathing.

Ms. Sanchez was in a motorcycle accident in which she lost the use of her right upper limb muscles due to significant nerve damage. However, when an electrode is inserted into her muscles, they are able to contract. Explain specifically why nerve damage caused her to lose the use of her muscles. Why can they still respond to stimulation from an electrode?

Damage to the nerves has impaired their ability to stimulate the muscle fibers, which means that the fibers will not receive the signal from the neuron to have an action potential or contract. However, the muscle fibers are still able to contract when stimulated by an electrode because the electrode triggers the initiation of an action potential along their sarcolemmas, which then leads to a contraction.

Catecholamine involved in movement and behavior

Dopamine

Neuropeptide involved in relief of pain

Endorphins

Ciliated cells in the CNS that produce and circulate the fluid around the brain and spinal cord

Ependymal cells

What would probably happen to bone with more osteoclast than osteoblast activity?

Excess osteoclast activity would mean that more ECM would be broken down than built, which would lead to progressive weakening of the bone.

What is thought to cause excess postexercise oxygen consumption?

Excessive postexercise oxygen consumption (EPOC) is due to the body's efforts to correct the disturbances to homeostasis that were brought on by exercise, including dissipating heat, restoring ion concentrations, and correcting blood pH.

The inorganic matrix of bone is solely responsible for the strength of bone tissue

False: Both the organic and inorganic matrices of bone are responsible for the strength of bone tissue

Osteoblasts are responsible for bone resorption, and osteoclasts are responsible for bone deposition

False: Osteoclasts are responsible for bone resorption, and osteoblasts are responsible for bone deposition

List some of the functions of smooth muscle tissue

Functions of smooth muscle include peristalsis, regulating the flow through organs such as blood vessels, and the formation of sphincters.

Toxins from the cone snail block glutamate receptors in the postsynaptic membrane. What will be the effect of these toxins?

Glutamate binds ionotropic postsynaptic receptors that trigger EPSPs in the postsynaptic neurons. Blocking glutamate receptors will prevent the generation of these EPSPs and reduce the number of action potentials fired in the CNS.

Predict the effects of the poison strychnine, which blocks glycine receptors on postsynaptic neurons of the CNS

Glycine typically triggers IPSPs and so has an inhibitory effect in the CNS. Blocking glycine receptors will increase the amount of inappropriate excitation in the CNS, leading to abnormal motor, sensory, and mental processes.

Some athletes will consume only protein for several days before a competition, which reduces the amount of glycogen in both the muscle fibers and the liver. What effect would this have on their ability to perform activities that require short, powerful bursts of activity? How would it affect their ability to perform endurance activities?

Glycogen stores are one of the main sources of energy for short, powerful bursts of activity. Therefore, protein loading in an athlete engaging in these types of activities would actually decrease his or her performance. An athlete engaging in light endurance-type activities would not likely suffer a great decrease in performance, as glycogen is not the primary fuel for these activities.

The light band containing only thin filaments

I band

You have finished exercising with a friend, who says that he is breathing rapidly because he must have "used up all of his oxygen." What do you tell him?

If your friend had truly "used up all of his oxygen," it would be because he was no longer breathing. Instead, the rapid rate of breathing, or excess postexercise oxygen consumption, is due to the body's attempt to correct homeostatic imbalances that result from exercise.

Guillain-Barré (GHEE-yawn bar-RAY) syndrome is caused by the patient's own immune system attacking the myelin sheath of PNS neurons. Predict the symptoms and effects of such a disease.

In a patient with this syndrome, conduction will slow significantly in PNS neurons due to destruction of myelin. This will decrease the delivery speed of motor impulses to muscles, leading to partial or full paralysis. It will also slow the delivery of sensory impulses to the CNS, leading to decreased sensation.

Explain how an action potential is propagated down an axon in continuous conduction. Why is saltatory conduction faster than continuous conduction?

In continuous conduction, the initial segment of the axolemma depolarizes to threshold and has an action potential, which depolarizes the next segment of the axolemma to threshold. This continues down the length of the axon. Saltatory conduction is faster than continuous conduction as only the nodes of Ranvier must be depolarized to threshold, allowing action potentials to "leap" down the length of the axon.

What would happen if the drug blocked K+ channels instead?

In this case, the drug would prevent the neuron from repolarizing. The neuron would remain depolarized and unable to generate another action potential.

What do you think would happen to the neuronal action potential if the concentration of sodium ions in the extracellular fluid decreased significantly, to the point of reversing the gradient?

In this hypothetical situation, the opening of sodium ion channels would lead to Na+ leaving the cytosol and entering the extracellular fluid. This would cause the cell to lose positive charges, and the cell would hyperpolarize instead of depolarize.

One of the medications used to treat asthma works by causing the formation of a compound that inactivates myosin light-chain kinase. What effect would this medication have on smooth muscle cells? Why do you think it would be used to treat asthma?

Inactivating myosin light-chain kinase is a key part of smooth muscle cell relaxation. Taking this medication will hopefully cause the smooth muscle cells of the airways to relax, allowing them to open and restore normal breathing.

The drug neostigmine blocks the actions of acetylcholinesterase in the synaptic cleft. What effect would this have on synaptic transmission? What effects might you expect to see as a result of this drug?

Initially, synaptic transmission is increased as the actions of acetylcholine are prolonged. However, eventually the postsynaptic cell becomes refractory to stimulation because its membrane is unable to repolarize, and so it cannot be depolarized again or have another action potential. This will decrease the excitation at synapses that use acetylcholine, including the neuromuscular junction.

Which of the following best describes the function of the anterior cruciate ligament?

It prevents anterior displacement of the tibia on the femur and hyperextension

Certain conditions cause ligamentous laxity, which means that the ligaments are very loose. Predict how this would affect synovial joints. Would it have the same effect on cartilaginous and fibrous joints? Why or why not?

Ligaments are important in supporting synovial joints. If the ligaments are too loose, they will not fulfill their supportive role, and the synovial joint will be more likely to allow abnormal motion, leading to injury such as dislocation. On the other hand, cartilaginous and fibrous joints do not rely on ligaments for stability, as these two joint types are inherently more stable.

Albert, the patient in question 3, takes the drug lithium, which reduces the permeability of the neuronal axolemma to Na+ (that is, it allows fewer Na+ to enter the axon). Predict the effect this would normally have on his neuronal action potentials. Do you think this drug would be beneficial or harmful, considering his condition?

Lithium would simply make the tetrodotoxin poisoning worse, as it would further decrease the ability of the neurons to generate and conduct action potentials. The drug should not be administered while the patient recovers from the poison.

Sequence the following list of events of a neuronal action potential by placing 1 next to the first event, 2 next to the second event, and so on.

Local potentials depolarize the membrane to threshold The activation gates of voltage-gated Na+ channels open, Na+ flood the cytoplasm, and depolarization occurs The inactivation gates of voltage-gated Na+ channels close as voltage-gated K+ channels open, K+ begin to exit the axon, and repolarization begins Repolarization continues and Na+ channels return to resting K+ continue to flow out of the axon until the membrane is hyperpolarized

Explain why engaging in 30-60 minutes of "aerobics" is promoted as an activity that "burns fat." Would you get this same "fat burning" from several 20-second sprints? Explain your answer in biochemical terms.

Long-lasting activities typically use all the available glucose and require the use of other fuels such as fatty acids. This is why aerobics are said to "burn fat." Short sprints will not produce this same effect because they use primarily glycolytic catabolism and glucose as a fuel.

A fitness trainer advises her client to lower a weight slowly and in a controlled manner to reduce the risk of injury. Which type of muscle contraction is being used when the weight is lowered? Explain why the trainer advises her client to train in this manner.

Lowering the weight is accomplished by an isotonic eccentric contraction, which involves lengthening of the muscle fibers. Such contractions can cause injury due to overstretching if they are not done in a controlled manner.

Which of the following is not a method by which the effects of neurotransmitters are terminated?

Movement back to the cell body by retrograde axonal transport

Ms. Karabekian suffers a vertebral fracture that damages a large number of ganglia, then loses feeling in much of her right leg. Is she likely to recover the function of these damaged neurons? Why or why not? (Hint: Are ganglia part of the CNS or PNS? What do ganglia contain?)

Ms. Karabekian might regain some sensation, but she is unlikely to recover fully. Ganglia contain the cell bodies of PNS neurons. These neurons have some limited ability to regenerate if the cell body is intact. However, since her cell bodies were damaged in the injury, her neurons are unlikely to regenerate.

The drug neostigmine blocks the activity of the enzyme acetylcholinesterase in the synaptic cleft. Predict the effects of this drug.

Neostigmine prolongs the activity of ACh in the synaptic cleft by preventing its nearly immediate breakdown by AChE. This prolongs the skeletal muscle contraction.

Would you expect to find motor units and recruitment in single-unit smooth muscle tissue and cardiac muscle tissue? Why or why not?

No, you would not find recruitment in single-unit smooth muscle tissue and cardiac muscle tissue, as both types contain muscle cells that are connected by gap junctions and so function as a unit. When the cells contract, they all contract together, so there are no cells left to recruit.

During a surgical procedure, an anesthesiologist administers to the patient an inhaled anesthetic agent that opens Cl− channels in the postsynaptic membranes of neurons in the brain. Explain why this would put the patient "to sleep" for the duration of the surgical procedure.

Opening Cl− channels will cause the neurons to hyperpolarize, making it very difficult to stimulate them to have an action potential. This slows neuronal activity in the brain, which puts the patient "to sleep" for the procedure.

Imagine you have just picked up a cup of coffee. List all the sensory, integrative, and motor functions that your nervous system is performing as you do so.

PNS neurons of the somatic sensory division deliver temperature, smell, and sight stimuli pertaining to the coffee to the CNS. In the CNS, different neurons integrate these stimuli. Then, PNS neurons of the somatic motor division coordinate lifting the cup of coffee to your mouth and taking a sip.

Uniaxial joint in which the rounded articular surface of one bone fits into a groove of another bone and is held in place by a ligamentous ring

Pivot joint

Cocaine blocks the reuptake of dopamine, causing a high level of dopamine that stimulates the postsynaptic receptors for an extended period. Explain why people who abuse cocaine eventually need more of the drug to reach an equivalent "high."

Prolonged abuse of the drug leads to synaptic fatigue; the number of dopamine receptors declines over time, and the remaining receptors become less sensitive to dopamine.

Biaxial joint in which each articular surface has both convex and concave regions

Saddle joint

Surround the cell bodies of neurons in the PNS

Satellite cells

Create the myelin sheath in the PNS

Schwann cells

Which of the following statements about the general functions of the nervous system is false?

Sensory stimuli are transmitted on sensory efferent fibers to a sensory receptor

How does a skeletal muscle fiber differ structurally from typical cells?

Skeletal muscle fibers are typically long, thin cells. Cylindrical myofibrils make up about 80% of their sarcoplasm, along with a large number of mitochondria and multiple nuclei. The myofibrils are surrounded by sarcoplasmic reticulum.

A drug that blocks Na+ channels in neurons does so not only in the axon but also in the dendrites and cell body. What overall effect would this have on action potential generation?

Such a drug would not only prevent the conduction of action potentials but also block the generation of local potentials. This would prevent the depolarization of the axon hillock to threshold, and thus the generation of action potentials.

What would happen to synaptic transmission if you blocked the degradation and/or reuptake of excitatory neurotransmitters in the synaptic cleft? What if the neurotransmitters were inhibitory?

Such blockage would prolong the actions of the neurotransmitters in the synaptic cleft, increasing excitation of the postsynaptic neurons. If you prolonged the actions of inhibitory neurotransmitters, you would decrease the excitation of postsynaptic neurons.

Sometimes diverging circuits split into excitatory and inhibitory paths. When might such a circuit be required? (Hint: Think about muscle contraction.)

Such circuits are required for certain types of muscle contractions, as these often involve both agonist and antagonist muscle groups, of which one group must be stimulated while the other must be inhibited.

Researchers discover a genetic mutation that leads to a lack of T-tubules in a person's skeletal muscle fibers. Predict the possible effects of such a mutation. (Hint: How would it impact the structure and function of a triad?)

The action potential would be unable to reach and open calcium ion channels in the terminal cisternae without T-tubules. This would prevent calcium ions from being released from the SR, which would in turn prevent contraction.

Why must a cell body be intact for an axon to regenerate? (Hint: What structure is housed only in the cell body, and what are its functions?)

The cell body must be intact because this is where the nucleus and all cellular "machinery" for protein synthesis are housed. Without an intact cell body, the neuron won't be able to produce the proteins needed for regeneration.

Your friend sits with her forearm flexed 45° at the elbow. You place a weight in her hand, and she notes that she has difficulty lifting it further. However, when she attempts to lift the weight with her forearm in a relaxed or neutral position, she has little trouble. Explain these differing results.

The difference in strength has to do with the difference in starting length of the muscle fibers. When your friend's arm was flexed at the elbow, her muscle fibers were shortened and therefore able to produce less tension due to increased overlap of the thin and thick filaments. However, when she picked it up from a relaxed or neutral position, the overlap of the filaments was ideal for maximal tension production.

How could a disease that affects primarily cartilage impact bone growth and bone formation?

The epiphyseal plate is composed of hyaline cartilage. Any disease that affects hyaline cartilage will impair the function of the epiphyseal plate, and therefore the structure and function of the bone as it grows.

Predict the effect of the poison ouabain (wah-BAY-in), which blocks Na+/K+ pumps, on the neuronal action potential. (Hint: What would happen to the sodium and potassium ion gradients?)

The gradients for Na+ and K+ change very little with a single action potential. However, the gradients will start to dissipate with repeated action potentials, and the poison will prevent the pumps from restoring them, reducing the ability of the neuron to have an action potential.

Sometimes when you pull your dinner out of the microwave you have to hold your fingertips to the food for a second or two before you can tell if it is hot or cold. Explain why this happens. (Hint: What type of fiber transmits temperature stimuli?)

The impulses are conducted relatively slowly because temperature sensations are carried on type C fibers, which are small and unmyelinated.

Predict how a poison that blocks voltage-gated calcium ion channels in the axon terminal would affect synaptic transmission.

The influx of calcium ions in the axon terminal is what triggers exocytosis of the synaptic vesicles. If these calcium ion channels are blocked, exocytosis will not be triggered, and synaptic transmission will effectively be halted.

Predict the effect that tetrodotoxin would have on Albert's muscle fiber action potentials (see question 3). Would it affect end-plate potentials at the motor end plate? Why or why not?

The poison would prevent the spread of action potentials along the sarcolemma of muscle fibers. The end-plate potentials at the motor end plate would not be directly affected, though, as they are generated by ligand-gated ion channels. However, because of the effect on action potentials, the neurons supplying the muscle fibers would be unable to stimulate those fibers.

Asthma is a respiratory disease involving the smooth muscle cells lining the airway passages of the lungs. When an asthmatic response is triggered, a pathway is initiated that causes two changes in the smooth muscle cells: (1) a release of calcium ions from the SR, and (2) increased binding of calcium ions with calmodulin. Predict the effect this would have on the smooth muscle cells of the airways and on a person's overall ability to breathe. Explain your answer.

The released calcium ions from the SR, combined with an increase in calcium ion binding to calmodulin, would trigger the activation of myosin light-chain kinase. This would lead to contraction of the muscle cells, and constriction (narrowing) of the airways.

Jesse is a 2-year-old boy who presents with difficulty in walking and poor control of movements. When the doctor examines Jesse, she notices that when his muscles contract, they are very slow to relax and remain contracted well after the movement has been performed. She sends a sample of his tissue for genetic analysis, and the lab reports a genetic defect that causes the pumps in the SR to operate much more slowly than normal. How does a defect in DNA lead to a malfunctioning protein? How does this finding explain Jesse's symptoms?

The segment of DNA that codes for a single protein is a gene. Each gene is a unique sequence of nucleic acids in the DNA that specifies a unique sequence of amino acids. When this sequence is modified, the resulting protein and its amino acid sequence are modified, often leading to a nonfunctional protein. Jesse's genetic defect prevents normal muscle relaxation by preventing the removal of calcium ions from the cytosol after a contraction.

Some health practitioners claim that the cranial bones are moveable and that they are able to move these bones to treat a variety of conditions. Is this likely to be true in an adult? Why or why not?

The sutures are fused fibrous joints that are synarthroses. No motion is allowed at these joints, and therefore the claims are unlikely to be true.

What is the basic mechanism of contraction at the level of myofilaments?

The thick and thin filaments slide past one another, which generates tension, as described by the sliding-filament mechanism of contraction. As multiple sarcomeres generate tension, the entire muscle fiber contracts.

Describe the three components of the neuromuscular junction

The three components of the neuromuscular junction are (1) the axon terminal of the motor neuron, which contains synaptic vesicles with the neurotransmitter acetylcholine; (2) the narrow synaptic cleft; and (3) the motor end plate of the muscle fiber, which contains acetylcholine receptors.

Suppose a new type of muscle fiber is discovered that has a high concentration of myoglobin, large numbers of mitochondria, and a well-developed blood supply. What do you think would be the primary energy source for this new muscle fiber type? Explain your answer. Is this new type likely to be resistant to fatigue? Why or why not?

This new fiber type would likely use primarily oxidative catabolism, as it has a ready supply of oxygen from myoglobin and blood vessels and a large number of mitochondria in which to carry out oxidative catabolism. Such fibers tend to be fatigue-resistant because they continue to produce adequate quantities of ATP for as long as chemical fuels are available.

A hypothetical poison blocks K+ leak channels. How would this affect the resting membrane potential of skeletal muscle fibers? Explain your reasoning.

This would cause the resting membrane potential to become progressively less negative (more positive), as potassium ions wouldn't leak out of the cell but sodium ions would continue to leak into the cell.

Explain how you could increase the likelihood that a certain neuron will reach threshold and have an action potential. (Hint: Think about the different types of summation.)

To make an action potential more likely, the number of EPSPs needs to be increased. This can occur via temporal summation, in which one or more neurons fire repeated action potentials and trigger multiple EPSPs in rapid succession. It can also occur via spatial summation, in which multiple neurons fire action potentials and trigger EPSPs all at the same time.

Which of the following influences bone remodeling?

Vitamins such as vitamins D, C, and K Intake of calcium ions Hormones such as estrogen and testosterone All of the above

Using biochemical terms, explain why lifting a stack of textbooks over and over again would likely make you feel fatigued more quickly than repeatedly lifting a single textbook. (Hint: What types of motor units are activated when more tension is needed?)

When more tension is needed, fast motor units are recruited in addition to slow motor units. These fast motor units are less fatigue-resistant than slow motor units, which is why you are likely to feel fatigued more quickly.

When you lift a heavy box, your muscles need to generate a stronger than average contraction. What will happen to the timing and frequency of nerve stimulation of your muscles, and why?

When you lift a heavy box, the muscle fibers will likely be stimulated at a very high rate, about 80-100 times per second. This will result in wave summation and fused tetanus, which are needed to produce a strong enough contraction.

Would you expect to find larger motor units in the postural muscles of the back or the muscles of the hand? Explain your answer.

You would expect to find larger motor units in the back. The hand requires precise motor control, which necessitates multiple small motor units.

Identify the following as properties of electrical synapses (ES), chemical synapses (CS), or both (B). a. The plasma membranes of presynaptic and postsynaptic neurons are joined by gap junctions. b. Transmission is unidirectional and delayed. c. A presynaptic neuron and a postsynaptic neuron are involved. d. The use of neurotransmitters packaged into synaptic vesicles is required. e. Transmission is nearly instantaneous and bidirectional.

a. ES b. CS c. B d. CS e. ES

Of the following statements, identify those that are properties of intramembranous ossification, endochondral ossification, or both. a. The bone is formed via a hyaline cartilage model. b. Bone tissue forms from ossification centers. c. Bone forms from within a mesenchyme membrane. d. The early spongy bone is formed, after which the early compact e. bone develops. f. The original primary bone is replaced with secondary bone. A bone collar forms, followed by the early spongy bone.

a. Endochondral b. Both c. Intramembranous d. Intramembranous e. Both f. Endochondral

Mark the following statements as true or false. If the statement is false, correct it to make it a true statement. a. Aggregates of Golgi apparatus and lysosomes form dark-staining Nissl bodies within the cell body. b. The axon contains a high density of ribosomes, rough endoplasmic reticulum, and Golgi apparatus. c. Axons arise from the axon hillock. d. Substances can move toward or away from the cell body through the axon via fast axonal transport.

a. False: Aggregates of rough endoplasmic reticulum form dark-staining Nissl bodies within the cell body. b. False: The cell body contains a high density of ribosomes, rough endoplasmic reticulum, and Golgi apparatus. c. True d. True

Mark the following statements as true or false. If a statement if false, correct it to make a true statement. a. An excitatory postsynaptic potential is caused by K+ or Cl− channels opening in the membrane of the postsynaptic neuron. b. Postsynaptic potentials may summate by spatial summation in which multiple neurons fire onto a single postsynaptic neuron. c. An inhibitory postsynaptic potential causes the membrane potential of the postsynaptic neuron to approach threshold. d. Spatial summation can combine two EPSPs, two IPSPs, or an EPSP and an IPSP.

a. False: An inhibitory postsynaptic potential is caused by K+ or Cl− channels opening in the membrane of the postsynaptic neuron. b. True c. False: An excitatory postsynaptic potential causes the membrane potential of the postsynaptic neuron to approach threshold. d. True

Mark the following statements as true or false. If a statement is false, correct it to make a true statement. a. A property of all muscle cells is elasticity, which means that the tissue is able to stretch. b. The common function of all types of muscle tissue is to generate tension. c. The plasma membrane of a muscle cell is called the sarcoplasmic reticulum. d. Muscle cells are contractile, conductive, distensible cells.

a. False: a property of all muscle cells is distensibility, which means that the tissue is able to stretch. b. True c. False: a muscle cell's plasma membrane is called the sarcolemma. d. True

Mark the following statements as true or false. If a statement is false, correct it to make a true statement. a. Muscle fibers generate more tension if the starting length of their sarcomeres is very short. b. Stimulation by a motor neuron before a muscle fiber has fully relaxed results in a condition called wave summation. c. Muscles that require a great deal of precise control will have large motor units. d. A muscle fiber changes length during isotonic concentric and isotonic eccentric contractions.

a. False: muscle fibers generate more tension if the resting length of their sarcomeres is 100-120% of their optimal length. b. True c. False: muscles that require a great deal of precise control will have small motor units. d. True

Mark the following statements as true or false. If a statement is false, correct it to make a true statement. a. Fibrous joints are united by collagen fibers. b. A syndesmosis is a type of cartilaginous joint. c. Cartilaginous joints are synarthroses. d. The joint between the two pubic bones and the intervertebral joints are examples of symphyses.

a. True b. False: A syndesmosis is a type of fibrous joint. c. False: Cartilaginous joints are synarthroses or amphiarthroses. d. True

Mark the following statements as true or false. If a statement is false, correct it to make a true statement. a. The resting membrane potential refers to the voltage difference across the membranes of excitable cells at rest. b. The concentration of Na+ is highest in the cytosol, and the concentration of K+ is highest in the extracellular fluid. c. The Na+/K+ pumps and gated channels maintain the Na+ and K+ gradients necessary for action potentials to occur. d. A depolarization is a change in membrane potential that makes the potential less negative.

a. True b. False: The concentration of Na+ is highest in the extracellular fluid, and the concentration of K+ is highest in the cytosol. c. True d. True

Mark the following statements as true or false. If a statement is false, correct it to make a true statement. a. The resting membrane potential refers to the voltage difference across the membranes of excitable cells at rest. b. The concentration of Na+ is highest in the cytosol, and the concentration of K+ is highest in the extracellular fluid. c. The Na+/K+ pumps and gated channels maintain the Na+ and K+ gradients necessary for action potentials to occur. d. A depolarization is a change in membrane potential that makes the potential less negative. e. A local potential is a change in membrane potential that conducts the long-distance signals of the nervous system.

a. True b. False: The concentration of Na+ is highest in the extracellular fluid, and the concentration of K+ is highest in the cytosol. c. True d. True e. False: An action potential is a change in membrane potential that conducts the long-distance signals of the nervous system.

Mark the following statements as true for smooth muscle tissue, cardiac muscle tissue, and/or skeletal muscle tissue. a. Actin attaches to dense bodies. b. Cells are joined by intercalated discs. c. The thick and thin filaments are arranged into sarcomeres. d. The thick filaments contain myosin heads along their entire length. e. The cells depolarize and contract as a unit. f. Ca2+ binding to troponin is the initiating event of contraction. g. Ca2+ binding to calmodulin is the initiating event of contraction. h. The sarcolemma has a distinct motor end plate.

a. smooth b. cardiac c. skeletal, cardiac d. smooth e. cardiac, some smooth f. skeletal, cardiac g. smooth h. skeletal

The _______ is the period of time during which it is impossible to stimulate a neuron to have an action potential, whereas the ______ is the period of time during which a larger-than-normal stimulus is required to elicit an action potential.

absolute refractory period; relative refractory period

Bone movement at a joint is described around an invisible line known as a/an:

amphiarthrosis.

The trigger for exocytosis of synaptic vesicles from the presynaptic neuron is:

arrival of an action potential at the axon terminal and influx of calcium ions

The articulating ends of bones of synovial joints are covered in ______. The remaining internal surfaces of the joint are lined by the ______, which produces synovial fluid. The entire joint is encased by the ______, which is composed of dense irregular collagenous connective tissue.

articular cartilage; synovial membrane; articular capsule

The part of the epiphysis that does not ossify during a person's lifetime is the

articular surface

Regulation of heart rate, blood pressure, and digestive functions is carried out by the:

autonomic nervous system

An axon is best defined as a process that

can generate action potentials

A ______ is characterized by multiple input neurons synapsing on one postsynaptic neuron

converging circuit

Long bones grow in length from the

epiphyseal plate

Resistance-type activities will likely rely on ______ energy sources, whereas endurance activities will probably rely on _______ energy sources

glycolytic; oxidative

The myelinated segment of an axon that is covered by a glial cell is called a/an ______; the gaps between glial cells where the axolemma is exposed are called _______.

internode; nodes of Ranvier

Thick filaments are composed of the protein

myosin

A muscle fiber relaxes when

the concentration of Ca2+ in the cytosol returns to resting levels

The branching pieces of bone in spongy bone are called

trabeculae

Predict what might happen to a muscle cell that is distensible but not elastic. What if the reverse were true—a muscle cell that is elastic but not distensible?

A muscle cell that is distensible but not elastic would be able to stretch but would not be able to return to its original resting length. A cell that is not distensible would not be able to stretch at all, irrespective of its elasticity.

Predict the effect that a parathyroid hormone-secreting tumor would have on bone tissue. What would happen to the concentration of calcium ions in the blood with such a condition?

A tumor that secretes parathyroid hormone would trigger excessive osteoclast activity, and the resulting breakdown of bone would lead to more frequent bone fractures. In addition, it would cause the concentration of calcium ions in the blood to be much higher than normal because the normal negative feedback loop would be ineffective.

A young girl develops a tumor that secretes excess estrogen. Predict the effect of this excessive secretion on her bone growth and final height.

A young girl with excessive estrogen secretion is likely to have a significant increase in longitudinal bone growth, but is also likely to suffer from premature closure of the epiphyseal plates. Her height would increase in the short term, but her adult height might be less than average

Explain why a person who is wheelchair-bound or bed-bound often has very low bone mass, especially in his or her legs

An individual who is not bearing weight regularly is not placing an adequate load on his or her bones. This leads to insufficient stimulation of bone deposition, and so bone resorption predominates. This leads to progressive loss of bone mass.

The disease osteogenesis imperfecta is characterized by defective collagen in the organic matrix of bone. Predict the effects of such a disease

Bones affected by osteogenesis imperfecta are extremely brittle, as they lack the collagen fibers to give them tensile strength. This makes them much more likely to fracture when subjected to even normal physical forces.

Correctly order the following steps of bone growth in length

Chondrocytes in the zone of proliferation divide by mitosis Chondrocytes enlarge and cease dividing Chondrocytes enter the zone of calcification and die as their matrix calcifies Calcified cartilage is replaced with bone in the zone of ossification

Correctly order the following steps of fracture repair, placing a 1 by the first step, a 2 by the second step, and so on

Damaged blood vessels bleed and fill the gap between the bone fragments with a hematoma Fibroblasts, chondroblasts, and blood vessels enter the clot, and the soft callus begins to bridge the gap between bone fragments Osteoblasts in the periosteum lay down a bone callus of primary bone The bone callus is remodeled and replaced with secondary bone

Which functional joint class includes freely moveable joints?

Diarthroses

Collagen fibers are one of the predominant parts of the inorganic matrix

False: Collagen fibers are one of the predominant parts of the organic matrix

Parathyroid hormone increases the blood calcium ion concentration by increasing the activity of osteoblasts.

False: Parathyroid hormone increases the blood calcium ion concentration by increasing the activity of osteoclasts

The greater the load the bone must carry, the more bone that is resorbed by osteoclasts.

False: The greater the load the bone must carry, the less bone that is resorbed by osteoclasts.

When articular cartilage is damaged, often fibrocartilage forms instead of new hyaline cartilage. Does fibrocartilage have the same properties as hyaline cartilage? Is it likely to provide the same type of surface as hyaline cartilage? Explain.

Fibrocartilage is very tough and functions as a good shock absorber in a joint. However, it contains large numbers of protein fibers, particularly collagen, and so it isn't as smooth as hyaline cartilage and is not as effective at reducing friction. For this reason, a synovial joint with fibrocartilage will not function as well as one with hyaline cartilage.

How can excessive growth hormone increase the size of bones even after the epiphyseal plates have closed?

Growth hormone also promotes appositional bone growth, so if it is secreted in excess, the bones will grow in width, even if they can no longer grow in length

Uniaxial joint in which the convex articular surface of one bone fits into a concave articular depression

Hinge joint

What might happen if sutures were fused at birth?

If the sutures in the skull were fully fused at birth, the brain tissues could not grow within the skull. The sutures do not fuse until later in life to allow for brain growth.

What would happen if tetrodotoxin instead blocked voltage-gated potassium ion channels in the sarcolemma?

If the voltage-gated potassium ion channels in the sarcolemma were blocked, it would prevent the cell from repolarizing. A cell that cannot repolarize will never be able to depolarize again, and so no further action potentials will be generated or propagated.

Which of the following correctly describes the function of a ligament?

It connects two bones to each other in a joint.

Lauren has hurt her knee playing soccer. She explains that during the match, someone tackled her, hitting her on the lateral side of her knee. You notice during your examination that she has excessive range of motion in her knee; specifically, you are able to hyperextend her knee and anteriorly displace her tibia on her femur. Her tibia also displaces laterally on her femur. What has likely happened to her knee? Explain.

Lauren has likely injured her anterior cruciate ligament, which normally prevents hyperextension of the knee and anterior displacement of the tibia. She has also likely injured her tibial collateral ligament, as it normally prevents the abnormal lateral tibial motion seen in the exam.

Marfan syndrome can affect connective tissues around joints and make ligaments loose. Predict how this might affect the range of motion of a biaxial joint.

Like any disorder or disease that affects the function of ligaments, Marfan syndrome can cause hypermobility of joints. In a person with this syndrome, a biaxial joint could have a significantly greater range of motion, allowing some hyperextension and possibly circumduction. The joint could be at risk for dislocation, as well, because the increased range of motion reduces its stability.

Why do you think that astronauts are often faced with decreased bone mass after returning from periods of prolonged weightlessness?

Load-bearing exercise exerts compression and tension on bones, which increases osteoblast activity. Astronauts in space for a long period are not able to engage in load-bearing activities, and so their osteoblasts are less stimulated than normal, leading to reduced bone mass

Lucy Dupre is a 2-year-old girl living in northern Canada. You notice that her growth seems abnormally slow and she has exhibited signs of weakened bones, including fractures. Her parents admit they have not supplemented her diet with vitamin D, as they feel that any supplementation is "unnatural" and "not organic." Explain why Lucy is having problems with her bones and bone growth.

Lucy lives in an environment in northern Canada where she likely receives inadequate amounts of ultraviolet radiation. This has decreased the amount of vitamin D synthesis taking place in her skin. This decrease, combined with the lack of vitamin D supplementation, has resulted in a severe lack of vitamin D overall and the consequent leaching of calcium ions out of her bones. Such a condition has led to her stunted growth and weakened bones.

Fouz Akkad is a 6-year-old girl who has been diagnosed with a rare genetic defect in which her lysosomes are unable to maintain an acidic pH. What are lysosomes? Why do lysosomes require an acidic pH? How will this affect the ability of certain bone cells to function? What consequences will this disease have on Fouz's bones?

Lysosomes are organelles that generally perform digestive functions. Their main enzymes for catalyzing these breakdown reactions are functional only at an acidic pH. The lysosomes of osteoclasts contain enzymes responsible for catalyzing reactions that break down the organic component of bone. If the lysosomes are unable to maintain an acidic pH, these enzymes cannot function. This will lead to an imbalance in which bone deposition abnormally dominates bone resorption.

Nutrient artery

Main source of blood to the medullary cavity

Predict what would happen if osteoclasts did not function properly during endochondral and intramembranous ossification

Osteoclasts function in both types of ossification to resorb the initial primary bone so that it can be replaced with secondary bone. If osteoclasts failed to function, the weaker, less organized primary bone would remain instead of being replaced. In addition, nonfunctional osteoclasts would result in the failure of the medullary cavity to form and enlarge during endochondral ossification

Nonaxial joint in which two flat surfaces glide over each other

Plane joint

Predict what would happen if primary bone were not replaced by secondary bone

Primary bone is much weaker than secondary bone because it has little inorganic matrix, which makes it much less able to resist compressive forces. In addition, the irregularly arranged collagen bundles make primary bone less resistant to tensile forces, which further weakens it.

Certain diseases cause the production of collagen that is weaker than normal. Predict how such diseases could affect the structure and function of gomphoses.

Such diseases can completely disrupt the structure of the gomphoses because the periodontal ligament that locks a tooth into the alveolus of the mandible or maxilla would not be strong enough to withstand the demands of chewing. The teeth would be at risk for falling out or being damaged, as they would no longer be structurally sound. When the structure is compromised, the function may be lost.

Explain how increased motion at a synchondrosis would impair the function of the joint.

Synchondroses are classified functionally as immoveable, and immobility is vital to their function. Usually these joints are involved in protection of and stability for the surrounding anatomical structures. Any motion at these joints would compromise these vital functions.

What is/are the function(s) of synovial fluid?

Synovial fluid lubricates a joint to reduce friction, absorbs shock, and helps deliver nutrients to cartilage cells

Explain why joint movement is often painful when a tendon—which is outside the joint—is injured.

Tendons generally pass over or around synovial joints on their way to their insertions on bones. When the muscle associated with an injured tendon is contracted, the tendon is pulled taut over the joint and this causes pain. As the joint is moved over and over again, the injured tendon will constantly be a source of pain.

Explain why young men who take anabolic steroids (which mimic the actions of testosterone) often display stunted growth and have an overall shorter stature.

Testosterone and other anabolic steroids accelerate the closure of the epiphyseal plates. If anabolic steroids are taken during adolescence, the elevated levels of androgens will cause the plates to close even more rapidly, which will lead to shorter stature.

The poison tetrodotoxin from the pufferfish blocks voltage-gated sodium ion channels in the sarcolemma. Predict the effect of this poison on the action potentials of the muscle fiber.

Tetrodotoxin will prevent Na+ from entering the cytosol when the voltage-gated channels are triggered to open by the end-plate potential. This will inhibit the depolarization phase of the action potential and prevent an action potential from propagating along the sarcolemma.

Which factors contribute to the stability of the hip joint?

The acetabulum is relatively deep, which allows the femoral head to fit inside it snugly. The fit is enhanced by the acetabular labrum, the articular capsule, and multiple ligaments.

Predict what might happen if the thin and thick filaments were unable to move relative to one another within a sarcomere.

The basic mechanism of contraction involves the sliding of thick and thin filaments past one another. If they were stationary in a myofibril, no contraction would occur and no tension would be generated.

Do you think the cranial bones are joined by synarthroses, amphiarthroses, or diarthroses? Explain.

The bones of the mature skull are joined by joints functionally classified as synarthroses. The sutures between skull bones are interlocked and become fused once an individual reaches skeletal maturity. This is important because these joints have evolved for protection of the underlying brain. If these joints were freely moveable or even slightly moveable, this protective function would be compromised.

In the condition known as drop foot, the foot and ankle are unable to dorsiflex. Predict the consequences of this condition for walking.

The condition drop foot leaves the foot in a plantarflexed position. Individuals with this condition drag their toes as they walk because they are unable to flatten their feet. As you might expect, this makes the knee and hip work harder, as they have to pull the foot up farther so that the pointed toes clear the ground with each step.

Malnutrition in children often leads to a decreased rate of mitosis in different cell populations. What effect would this have on growth at the epiphyseal plate? Explain.

The decreased rate of mitosis would reduce the number of chondroblasts at the epiphyseal plate, and therefore slow the production of hyaline cartilage and the longitudinal growth of the bones. In addition, malnutrition would lead to an insufficient intake of calcium salts, vitamin D, vitamin C, and other nutrients needed for ossification, which could weaken the bones and further delay their growth

Sometimes a bone is injured at the epiphyseal plate. Predict the long-term effect this might have on the injured bone.

The epiphyseal plate is the structure from which a bone grows in length. If this structure is damaged, longitudinal growth could be impacted, and the bone on one side of the body could be shorter than the same bone on the other side of the body.

How does the structure of compact bone follow its function?

The function of compact bone is to provide a hard outer shell that resists all types of forces and protects the inner spongy bone and marrow. The concentric rings of bone matrix that characterize compact bone make it extremely strong and hard and enable it to perform these functions.

Some individuals have an abnormally small and shallow glenoid labrum. How would this affect the stability of the shoulder joint?

The head of the humerus doesn't fit very snugly into the glenoid cavity, as the cavity is too shallow. The glenoid labrum helps improve this fit and provides the shoulder with extra stability. If the glenoid labrum is smaller than normal, the degree of fit decreases, leading to instability and possibly chronic dislocations of the shoulder joint.

A surgical procedure called a fusion takes two bones and joins them, making them functionally one bone. What functional class of joint does this resemble? What properties would the fused joint have?

The joint resulting from this surgical procedure resembles a synarthrosis. The fused joint would no longer have a synovial cavity or hyaline articular cartilage and would be more stable than mobile.

Predict the potential consequences of damaging the nutrient artery in a bone injury. How would this affect the ability of the bone to heal?

The nutrient artery supplies a good portion of the blood flow to the bone. If this artery is damaged, portions of the bone could be cut off from the normal blood supply, which could lead to further bone injury. A bone with a damaged nutrient artery will take longer to heal because it will lack sufficient blood flow to deliver adequate oxygen, nutrients, and other components vital to healing.

It used to be common practice in surgical fracture repair to strip and remove the periosteum. Now, however, surgeons take great care to avoid damaging the periosteum. Explain why, and describe what would likely happen to bone healing with the periosteum missing.

The periosteum is where the majority of the osteoblasts reside. Osteoblasts are needed in fracture repair to rebuild the bone and bridge the gap between bone fragments. If the periosteum is stripped, bone healing will occur much more slowly because the population of osteoblasts will be dramatically reduced.

The disease myasthenia gravis (my′-uss-THEE-nee-ah GRAH-viss) results in the destruction of acetylcholine receptors on the motor end plate. Predict the symptoms and effects of this disease.

The progressive destruction of ACh receptors leads to a progressive decline in the strength of end-plate potentials. This will make it harder for a neuron to elicit action potentials, resulting in muscle weakness and partial or full paralysis.

How could diseases of the kidney, skin, and/or intestines cause diseases of the bone?

The skin is involved in the production of vitamin D, and the kidneys and intestines must be able to absorb calcium ions into the blood. If any of these organs are diseased and unable to perform their functions, levels of vitamin D and/or calcium ions in the blood will be inadequate to maintain bone mass.

A hypothetical poison denatures the protein titin, making it straight instead of spring-shaped. Predict the effect of this change on muscle tissue.

The spring shape of titin allows it to perform its primary functions, which are to hold thick filaments in place, help return the thick filaments to their resting positions after a contraction, and provide the muscle fiber with elasticity. Were titin to lose this structure, it would not be able to adequately perform its function. The thick filaments would be less likely to return to their normal resting positions after a contraction, and the sarcomere might not return to its normal resting length.

The primary action of the biceps brachii muscle of the anterior arm is to flex the forearm at the elbow. However, when this muscle is inflamed, pain is felt in the shoulder. Explain this finding.

The tendon of the biceps brachii muscle passes through the articular capsule of the shoulder joint as it attaches to its origin point. For this reason, inflammation of the tendon in this area leads to inflammation in the articular capsule of the shoulder joint. This causes pain on movement of the joint.

Predict the effect of improperly functioning troponin that isn't able to bind to tropomyosin.

The troponin-tropomyosin interaction is necessary to regulate contraction and relaxation. Were troponin unable to bind tropomyosin, it would not be able to hold tropomyosin in place when the muscle is not contracting, and it would not be able to move it away from the active sites on actin to initiate a contraction.

Predict how the functions of the human hand would be different if the carpometacarpal joint of the thumb were a uniaxial hinge joint instead of a saddle joint.

This change to the structure of the thumb joint would completely alter the functional capability of the hand. The special movement of opposition would be lost, as a uniaxial hinge joint would not allow that type of movement. The thumb would move around only a single axis, allowing for flexion and extension similar to that of the other digits of the hand, but not allowing abduction and adduction. Grasping and holding objects, abilities that are taken for granted, would be severely limited if the thumb joint were uniaxial.

Bone resorption is triggered by pressure placed on the bone.

True

Calcitonin is released in response to an elevated calcium ion concentration in the blood

True

Osteocytes are mature and less active osteoblasts that have become surrounded by bone ECM

True

The collagen fibers of bone help it to resist torsion and tension

True

Vitamin D is required for calcium ion absorption from the intestines and retention in the kidneys.

True

Suppose that a new type of muscle tissue is discovered and, like the other types, it generates tension. Would you expect this new tissue type to have the same basic structure as skeletal, smooth, and cardiac muscle tissues? Why or why not?

We would expect the new type of muscle tissue to have structural elements similar to those of the other three types of muscle tissue. This is due to the structure-function relationship—the new muscle tissue type has the same function as the other types, so it would likely have a similar structure.

Explain the differences between red bone marrow and yellow bone marrow

Yellow bone marrow consists largely of adipose tissue, whereas red bone marrow contains the hematopoietic stem cells that form all formed elements of the blood

Mark the following statements as true or false. If a statement is false, correct it to make a true statement. a. The knee and the elbow are multiaxial joints. b. The elbow joint consists of two separate articulations. c. The patella is encased within the tendon of the quadriceps femoris muscle group. d. The shoulder joint is stabilized by the medial and lateral menisci. e. The hip joint is less stable than the shoulder joint, but it allows more motion.

a. False: The knee and the elbow are uniaxial joints. b. True c. True d. False: The knee joint is stabilized by the medial and lateral menisci. e. False: The shoulder joint is less stable than the hip joint, but it allows more motion.

Define each of the following movements or movement pairs. a. Flexion and extension b. Adduction and abduction c. Rotation d. Circumduction e. Dorsiflexion and plantarflexion f. Elevation and depression

a. Flexion decreases the angle between two bones, and extension increases the angle between two bones. b. Adduction moves a body part toward the body's midline, and abduction moves it away from the midline. c. Rotation is the turning of a bone along its own longitudinal axis. d. Circumduction is movement of a bone in a cone-shaped radius. e. Dorsiflexion is the movement of the foot and ankle toward the leg, and plantarflexion is the movement of the foot and ankle away from the leg. f. Elevation is movement of a body part in a superior direction, and depression is movement in an inferior direction.

Explain the effect that the following hormones have on growth of bone tissue: a. Growth hormone b. Testosterone c. Estrogen

a. Growth hormone increases both longitudinal and appositional growth by increasing the rate of mitosis of chondrocytes in the epiphyseal plate, increasing the activity of osteogenic cells, and directly stimulating the osteoblasts in the periosteum. b. Testosterone increases the rate of appositional bone growth, the rate of calcium ion deposition, and the rate of mitosis at the epiphyseal plate. It also accelerates closure of the epiphyseal plate. c. Estrogen increases the rate of mitosis of chondrocytes at the epiphyseal plate, inhibits osteoclasts, and accelerates closure of the epiphyseal plate.

Predict the consequences that an injury to each of the following ligaments would have for the function and range of motion of the knee. a. Anterior cruciate ligament b. Tibial collateral ligament c. Posterior cruciate ligament

a. The anterior cruciate ligament runs from an anterior insertion site on the tibia to the posterior aspect of the femur. When the knee is extended, this ligament is pulled taut to prevent hyperextension. The injured ligament would permit an increase in the amount of extension or hyperextension, allowing the tibia to move too far anteriorly on the femur. b. The tibial collateral ligament supports the medial aspect of the knee joint and prevents the lower leg from moving too far laterally relative to the thigh at the knee joint. The injured ligament would allow too much lateral movement of the lower leg relative to the thigh at the knee joint. c. The posterior cruciate ligament is found just posterior to the anterior cruciate ligament and runs from the anteroinferior femur to the posterior side of the tibia. This ligament is pulled tightly when the knee is flexed to prevent hyperflexion and dislocation of the tibia from the femur. The injured ligament would allow an increased amount of flexion at the knee, and the tibia would be at risk for being dislocated from the femur posteriorly.

Explain how the structure of each of the following joint types follows its function. a. Fibrous joint b. Cartilaginous joint c. Synovial joint

a. The primary function of fibrous joints is stability, or maintaining bones in certain positions relative to other bones. These joints consist of bones united by collagen fibers, which prevent them from moving freely and give them stability. b. Most cartilaginous joints (except the epiphyseal plate) must both be stable and allow for motion. The fibrocartilage that joins the bones in these joints is flexible, which allows some motion, but it is also tough, which provides stability. c. Synovial joints must allow for a significant amount of motion between two bones. This is made possible by the fact that the two articulating bones are separated by a fluid-filled joint cavity.

In general, when mobility of a joint _______, its stability _______.

increases; decreases

Bone deposition is carried out by ______, which secrete the ______ of the ECM by exocytosis. They facilitate the formation of the ______ of the ECM by secreting filled with calcium ions, enzymes, and ATP. Bone resorption is carried out by _______, which secrete ______ and _______ from their ruffled border.

osteoblasts, organic matrix; inorganic matrix, vesicles; osteoclasts, hydrogen ions, enzymes

The subunit of compact bone is the ______. It consists of rings of bone matrix called ______ that surround a structure called the ______ that contains blood vessels and nerves. Other structures called _______ also contain blood vessels and nerves. Osteocytes are housed in and communicate via _______.

osteon; lamellae, central canal; perforating canals; lacunae, canaliculi

The structure that stabilizes the shoulder joint is known as the

rotator cuff