PHA 404 Physiology Exam 2

3. What conditions will produce the maximum tension in a skeletal muscle fiber?

Maximum tension is produced when the fiber is (a) stimulated by an action potential frequency that is high enough to produce a maximal tetanic tension and (b) at its optimum length L0, where the thick and thin filaments have overlap sufficient to provide the greatest number of cross-bridges for tension production.

4. A skeletal muscle can often maintain a moderate level of active tension for long periods of time, even though many of its fibers become fatigued. Explain

Moderate tension—for example, 50% of maximal tension—is accomplished by recruiting sufficient numbers of motor units to produce this degree of tension. If activity is maintained at this level for prolonged periods, some of the active fibers will begin to fatigue and their contribution to the total tension will decrease. The same level of total tension can be maintained, however, by recruiting new motor units as some of the original ones fatigue. At this point, for example, one may have 50% of the fibers active, 25% fatigued, and 25% still unrecruited. Eventually, when all the fibers have fatigued and there are no additional motor units to recruit, the whole muscle will fatigue.

1. A person is found to have a hematocrit of 35%. Can you conclude that there is a decreased volume of erythrocytes in the blood? Explain. Hint: See Figure 12.1 and remember the formula for hematocrit.

No. Decreased erythrocyte volume is certainly one possible explanation, but there is a second: The person may have a normal erythrocyte volume but an increased plasma volume. Convince yourself of this by writing the hematocrit equation as Erythrocyte volume/(Erythrocyte volume + Plasma volume)

1. Describe several mechanisms by which pain could theoretically be controlled medically or surgically

(a) Use drugs to block transmission in the pathways that convey information about pain to the brain. For example, if substance P is the neurotransmitter at the central endings of the nociceptor afferent fibers, give a drug that blocks the substance P receptors. (b) Cut the dorsal root at the level of entry of the nociceptor fibers to prevent transmission of their action potentials into the central nervous system. (c) Give a drug that activates receptors in the descending pathways that block transmission of the incoming or ascending pain information. (d) Stimulate the neurons in these same descending pathways to increase their blocking activity (stimulation-produced analgesia or, possibly, acupuncture). (e) Cut the ascending pathways that transmit information from the nociceptor afferents. (f) Deal with emotions, attitudes, memories, and so on to decrease sensitivity to the pain. (g) Stimulate nonpain, low-threshold afferent fibers to block transmission through the pain pathways (TENS). (h) Block transmission in the afferent nerve with a local anesthetic such as Novocaine or Lidocaine.

12. A person's cardiac output is 7 L/min and mean arterial pressure is 140 mmHg. What is the person's total peripheral resistance? Hint: See Table 12.8 and recall the equation relating MAP, CO, and TPR.

20 mmHg/L per minute. TPR = MAP/CO.

2. The left AV valve has only two large leaflets, while the right AV valve has three smaller leaflets. It is a general principle of physiology that structure is a determinant of—and has coevolved with—function. Although it is unknown why the two valves differ in structure in this way, what difference in the functional demands of the left side of the heart might explain why there is one less valve leaflet than on the right side?

Although it is possible that the difference in valve leaflet number is simply a random quirk of how the heart develops, a clear difference in the functional demands on the two AV valves is the amount of pressure they must withstand. At the peak of systole, the typical pressure gradient across the right AV valve is approximately 25 mmHg (pulmonary systolic pressure), while across the left AV valve it is approximately 120 mmHg (systemic systolic pressure). Having one less valve leaflet, the left AV valve has a smaller area where the edges of valve leaflets must seal. It seems likely that this structure makes it less susceptible to failure despite the greater pressure it encounters

Elaboration of surface area to maximize functional capability is a common motif in the body illustrating the general principle of physiology that structure is a determinant of—and has coevolved with—function. Cite an example from this chapter.

An excellent example of a body structure that has maximized surface area to maximize function is a photoreceptor cell. Repeated foldings of the membranous discs in rods and cones greatly increases the surface area available for the retinal-containing photopigments, making the eye exquisitely sensitive to light.

6. As a result of an automobile accident, 50% of the muscle fibers in the biceps muscle of a patient were destroyed. Ten months later, the biceps muscle was able to generate 80% of its original force. Describe the changes that took place in the damaged muscle that enabled it to recover

Two factors lead to the recovery of muscle force. (a) Some new fibers can be formed by the fusion and development of undifferentiated satellite cells. This will replace some, but not all, of the fibers that were damaged. (b) Some of the restored force results from hypertrophy of the surviving fibers. Because of the loss of fibers in the accident, the remaining fibers must produce more force to move a given load. The remaining fibers undergo increased synthesis of actin and myosin, resulting in increases in fiber diameter and, consequently, their force of contraction

1. Which of the following corresponds to the state of myosin (M) under resting conditions, and which corresponds to rigor mortis? (a) M · ATP (b) M · ADP · Pi (c) A · M · ADP · Pi (d) A · M

Under resting conditions, the myosin has already bound and hydrolyzed a molecule of ATP, resulting in an energized molecule of myosin (M · ADP · Pi). Because ATP is necessary to detach the myosin cross-bridge from actin at the end of cross-bridge movement, the absence of ATP will result in rigor mortis, in which case the cross-bridges become bound to actin but do not detach, leaving myosin bound to actin (A · M).

Which correctly describes a step in auditory signal transduction? a. Displacement of the basilar membrane with respect to the tectorial membrane stimulates stereocilia on the hair cells. b. Pressure waves on the oval window cause vibrations of the malleus, which are transferred via the stapes to the round window. c. Movement of the stapes causes oscillations in the tympanic membrane, which is in contact with the endolymph. d. Oscillations of the stapes against the oval window set up pressure waves in the semicircular canals. e. The malleus, incus, and stapes are found in the inner ear, within the cochlea.

a. Pressure waves traveling down the cochlea make the cochlear duct vibrate, moving the basilar membrane against the stationary tectorial membrane and bending the hair cells that bridge the gap between the two.

4. What region of the brain contains the primary visual cortex? a. the occipital lobe b. the frontal lobe c. the temporal lobe d. the somatosensory cortex e. the parietal lobe association area

a. The occipital lobe of the cortex is the initial site of visual processing. (Review Figure 7.13.)

Damage to what parts of the cerebral cortex could explain the following behaviors? (a) A person walks into a chair placed in her path. (b) The person does not walk into the chair, but she does not know what the chair can be used for.

appear in shades of gray, with no color vision. In very bright light, there would be no vision because of bleaching of the rods' rhodopsin.

A key general principle of physiology is that homeostasis is essential for health and survival. How might sensory receptors responsible for detecting painful stimuli (nociceptors) contribute to homeostasis?

Nociceptors detect stimuli indicating potential or actual damage to tissues, which could threaten homeostasis. By allowing us to perceive those stimuli, nociceptors not only help us to learn to avoid them but also let us respond quickly to minimize damage when they occur (like quickly removing your hand from a hot stove burner). In these ways, we can avoid injuries like burns or cuts that may threaten homeostasis by causing fluid loss from the body. As another example, pain stops us temporarily from overusing injured limbs, giving them time to heal so that our ability to move and obtain food or avoid life-threatening situations is not permanently impaired.

1. What changes would occur in the knee-jerk reflex after destruction of the gamma motor neurons? Hint: Think about whether the intrafusal fibers are stretched or flaccid when this test is performed.

None. The gamma motor neurons are important in preventing the muscle-spindle stretch receptors from going slack, but when this reflex is tested, the intrafusal fibers are not flaccid. The test is performed with a bent knee, which stretches the extensor muscles in the thigh (and the intrafusal fibers within the stretch receptors). The stretch receptors are therefore responsive.

10. The disease tetanus results when a bacterial toxin blocks the release of inhibitory neurotransmitter

T. Clostridium tetani toxin specifically blocks the release of neurotransmitter from neurons that normally inhibit motor neurons. The resulting imbalance of excitatory and inhibitory inputs causes spastic contractions of muscles

6. Neurons in the primary motor cortex of the right cerebral hemisphere mainly control muscles on the left side of the body.

T. Most descending corticospinal pathways cross the midline of the body in the medulla oblongata.

3. Draw a cross section of the spinal cord and a portion of the thigh (similar to Figure 10.6) and "wire up" and activate the neurons so the leg becomes a stiff pillar, that is, so the knee does not bend. Hint: Remember to include both extensors and flexors.

The drawing must have excitatory synapses on the motor neurons of both ipsilateral extensor and ipsilateral flexor muscles

9. A person is given a drug that doubles the blood flow to her kidneys but does not change the mean arterial pressure. What must the drug be doing? Hint: See Figure 12.36 and remember how parallel resistances add up.

The drug must have caused the arterioles in the kidneys to dilate enough to reduce their resistance by 50%. Blood flow to an organ is determined by mean arterial pressure and the organ's resistance to flow. Another important point can be deduced here: If mean arterial pressure has not changed even though renal resistance has dropped 50%, then either the resistance of some other organ or actual cardiac output has increased.

2. What changes would occur in the knee-jerk reflex after destruction of the alpha motor neurons? Hint: See Figure 10.5; what are the functions of alpha motor neurons?

The efferent pathway of the reflex arc (the alpha motor neurons) would not be activated, the effector cells (the extrafusal muscle fibers) would not be activated, and there would be no reflexive response.

10. A blood vessel removed from an experimental animal dilates when exposed to acetylcholine. After the endothelium is scraped from the lumen of the vessel, it no longer dilates in response to this mediator. Explain. Hint: See Table 12.6.

The experiment suggests that acetylcholine causes vasodilation by releasing nitric oxide or some other vasodilator from endothelial cells.

2. A general principle of physiology states that physiological processes are dictated by the laws of chemistry and physics. The chemical law of mass action tells us that the rate of a chemical reaction will slow down when there is a buildup in concentration of products of the reaction. How can this principle be applied as a contributing factor in muscle fatigue?

The forward motion of cross-bridges during the cross-bridge cycle (power stroke) is associated with a chemical reaction in which ADP and Pi are released as products (see step 2 in Figure 9.15). During high-frequency stimulation of muscles when cross-bridges cycle repeatedly, the concentrations of ADP and Pi build up in the muscle cytosol. Due to the law of mass action, the buildup of these products inhibits the rate of the chemical reaction and, thus, the power stroke of the cross-bridge cycle. This contributes to the reduction of contraction speed and force that occurs when muscles are fatigued.

5. A person has a left ventricular systolic pressure of 180 mmHg and an aortic systolic pressure of 110 mmHg. What is the explanation? Hint: See Figure 12.22.

The person has a narrowed aortic valve. Normally, the resistance across the aortic valve is so small that there is only a tiny pressure difference between the left ventricle and the aorta during ventricular ejection. In the example given here, the large pressure difference indicates that resistance across the valve must be very high.

3. If all plasma membrane Ca2+ channels in contractile cardiac muscle cells were blocked with a drug, what would happen to the muscle's action potentials and contraction? Hint: See Figure 12.15

The plateau of the action potential and the contraction would be absent. You may think that contraction would persist because most Ca2+ in excitation-contraction coupling in the heart comes from the sarcoplasmic reticulum. However, the signal for the release of this Ca2+ is the Ca2+ entering across the plasma membrane.

1. One of the general principles of physiology introduced in Chapter 1 states that most physiological functions are controlled by multiple regulatory systems, often working in opposition. However, skeletal muscle cells are only innervated by alpha motor neurons, which always release acetylcholine and always excite them to contract. By what mechanism are skeletal muscles induced to relax?

Unlike smooth and cardiac muscle cells, which are regulated directly by both excitatory and inhibitory inputs, skeletal muscle fibers only have excitatory inputs, so must be inhibited indirectly. They are inhibited from contracting when there are no action potentials arriving along their associated alpha motor neurons, so inhibition must occur at the level of the alpha motor neurons. The dendrites and cell bodies of alpha motor neurons found in the brainstem and spinal cord receive both excitatory and inhibitory inputs from interneurons, sensory neurons, and neurons in descending pathways. When the inhibitory inputs predominate, the alpha motor neuron does not generate action potentials and the muscle fibers it innervates remain relaxed.

10. You attach a skeletal muscle cell to a force transducer and measure total isometric tension during stimulation at a series of different cell lengths, from short to very long. Draw a graph showing how the total tension would vary with cell length

The total tension would be the sum of the active and passive tension at each length. Here is a sketch of the graph (dotted line) superimposed on Figure 9.21

16. If a woman's mean arterial pressure is 85 mmHg and her systolic pressure is 105 mmHg, what is her pulse pressure? Hint: See Figure 12.34 and Table 12.8.

Using the following equation, MAP = DP + 1/3(SP − DP), inserting 85 for MAP and 105 for SP, solving for DP gives a value of 75 mmHg. Pulse pressure = SP − DP, or in this case, 105 − 75 = 30 mmHg.

1. Which is a false statement about skeletal muscle structure? a. A myofibril is composed of multiple muscle fibers. b. Most skeletal muscles attach to bones by connective-tissue tendons. c. Each end of a thick filament is surrounded by six thin filaments. d. A cross-bridge is a portion of the myosin molecule. e. Thin filaments contain actin, tropomyosin, and troponin.

a. A single skeletal muscle fiber, or cell, is composed of many myofibrils.

3. Which would result in reflex contraction of the extensor muscles of the right leg? a. stepping on a tack with the left foot b. stretching the flexor muscles in the right leg c. dropping a hammer on the right big toe d. action potentials from nociceptors of the right leg e. action potentials from muscle-spindle receptors in flexors of the right leg

a. Afferent action potentials from pain receptors in the injured left foot would stimulate the withdrawal reflex of the left leg (activation of flexor muscles and inhibition of extensors) and the opposite pattern in the right leg (the crossed-extensor reflex).

Choose the true statement: a. The modality of energy a given sensory receptor responds to in normal functioning is known as the "adequate stimulus" for that receptor. b. Receptor potentials are "all-or-none," that is, they have the same magnitude regardless of the strength of the stimulus. c. When the frequency of action potentials along sensory neurons is constant as long as a stimulus continues, it is called "adaptation." d. When sensory units have large receptive fields, the acuity of perception is greater. e. The "modality" refers to the intensity of a given stimulus.

a. For example, photons of light are the adequate stimulus for photoreceptors of the eye, and sound is the adequate stimulus for hair cells of the ear.

14. When a person engages in strenuous, prolonged exercise, a. blood flow to the kidneys is reduced. b. cardiac output is reduced. c. total peripheral resistance increases. d. systolic arterial blood pressure is reduced. e. blood flow to the brain is reduced.

a. Increased sympathetic nerve firing and norepinephrine release during exercise constrict vascular beds in the kidneys, GI tract, and other tissues to compensate for the large dilation of muscle vascular beds.

7. Which of the following would not result in tissue edema? a. an increase in the concentration of plasma proteins b. an increase in the pore size of systemic capillaries c. an increase in venous pressure d. blockage of lymph vessels e. a decrease in the protein concentration of the plasma

a. Increasing colloid osmotic pressure would decrease filtration of fluid from capillaries into the tissues.

1. Which is a correct statement regarding the hierarchical organization of motor control? a. Skeletal muscle contraction can only be initiated by neurons in the cerebral cortex. b. The basal nuclei participate in the creation of a motor program that specifies the pattern of neural activity required for a voluntary movement. c. Neurons in the cerebellum have long axons that synapse directly on alpha motor neurons in the ventral horn of the spinal cord. d. The cell bodies of alpha motor neurons are found in the primary motor region of the cerebral cortex. e. Neurons with cell bodies in the basal nuclei can form either excitatory or inhibitory synapses onto skeletal muscle cells.

b. The basal nuclei, sensorimotor cortex, thalamus, brainstem, and cerebellum are all middle-level structures that create a motor program based on the intention to carry out a voluntary movement.

9. The function of myosin light-chain kinase in smooth muscle is to a. bind to calcium ions to initiate excitation-contraction coupling. b. phosphorylate cross-bridges, thus driving them to bind with the thin filament. c. split ATP to provide the energy for the power stroke of the cross-bridge cycle. d. dephosphorylate myosin light chains of the cross-bridge, thus relaxing the muscle. e. pump Ca2+ from the cytosol back into the sarcoplasmic reticulum.

b. When myosin-light-chain kinase transfers a phosphate group from ATP to the myosin light chains of the cross-bridges, binding and cycling of cross-bridges are activated.

13. Which correctly pairs an ECG phase with the cardiac event responsible? a. P wave: depolarization of the ventricles b. P wave: depolarization of the AV node c. QRS wave: depolarization of the ventricles d. QRS wave: repolarization of the ventricles e. T wave: repolarization of the atria

c

2. The principal site of erythrocyte production is a. the liver. b. the kidneys. c. the bone marrow. d. the spleen. e. the lymph nodes.

c

5. Where is the primary motor cortex found? a. in the cerebellum b. in the occipital lobe of the cerebrum c. between the somatosensory cortex and the premotor area of the cerebrum d. in the ventral horn of the spinal cord e. just posterior to the parietal lobe association cortex

c

Which of the following contains blood with the lowest oxygen content? a. aorta b. left atrium c. right ventricle d. pulmonary veins e. systemic arterioles

c. Blood in the right ventricle is relatively deoxygenated after returning from the tissues.

5. Which of the following correctly ranks pressures during isovolumetric contraction of a normal cardiac cycle? a. left ventricular > aortic > left atrial b. aortic > left atrial > left ventricular c. left atrial > aortic > left ventricular d. aortic > left ventricular > left atrial e. left ventricular > left atrial > aortic

d

Which category of taste receptor cells does MSG (monosodium glutamate) most strongly stimulate? a. salty b. bitter c. sweet d. umami e. sour

d. "Umami" is derived from the Japanese word meaning "delicious" or "savory"; the stimulation of these taste receptors by glutamate produces the perception of a rich, meaty flavor.

4. If implanted electrodes were used to stimulate action potentials in gamma motor neurons to flexors of the left arm, which would be the most likely result? a. inhibition of the flexors of the left arm b. a decrease in action potentials from muscle-spindle receptors in the left arm c. a decrease in action potentials from Golgi tendon organs in the left arm d. an increase in action potentials along alpha motor neurons to flexors in the left arm e. contraction of flexor muscles in the right arm

d. Activating the gamma motor neurons would cause contraction of the ends of intrafusal muscle fibers, stretching the musclespindle receptors, and the resulting action potentials would monosynaptically excite the alpha motor neurons innervating the extrafusal fibers of the stretch receptors.

4. During excitation-contraction coupling in a skeletal muscle fiber, a. the Ca2+-ATPase pumps Ca2+ into the T-tubule. b. action potentials propagate along the membrane of the sarcoplasmic reticulum. c. Ca2+ floods the cytosol through the dihydropyridine (DHP) receptors. d. DHP receptors trigger the opening of terminal cisternae ryanodine receptor Ca2+ channels. e. acetylcholine opens the DHP receptor channel.

d. DHP receptors act as voltage sensors in the T-tubule membrane and are physically linked to ryanodine receptors in the sarcoplasmic reticulum membrane. When an action potential depolarizes the T-tubule membrane, DHP receptors change conformation and trigger the opening of the ryanodine receptors. This allows Ca2+ to diffuse from the interior of the sarcoplasmic reticulum into the cytosol.

7. Which correctly characterizes a "fast-oxidative-glycolytic" type of skeletal muscle fiber? a. few mitochondria and high glycogen content b. low myosin ATPase rate and few surrounding capillaries c. low glycolytic enzyme activity and intermediate contraction velocity d. high myoglobin content and intermediate glycolytic enzyme activity e. small fiber diameter and fast onset of fatigue

d. Fast-oxidative-glycolytic fibers are an intermediate type that are designed to contract rapidly but to resist fatigue. They utilize both aerobic and anaerobic energy systems; thus, they are red fibers with high myoglobin (which facilitates production of ATP by oxidative phosphorylation), but they also have a moderate ability to generate ATP through glycolytic pathways.

Which best describes "lateral inhibition" in sensory processing? a. Presynaptic axo-axonal synapses reduce neurotransmitter release at excitatory synapses. b. When a stimulus is maintained for a long time, action potentials from sensory receptors decrease in frequency with time. c. Descending inputs from the brainstem inhibit afferent pain pathways in the spinal cord. d. Inhibitory interneurons decrease action potentials from receptors at the periphery of a stimulated region. e. Receptor potentials increase in magnitude with the strength of a stimulus.

d. Lateral inhibition increases the contrast between the region at the center of a stimulus and regions at the edges of the stimulus, which increases the acuity of stimulus localization.

8. Which statement comparing the systemic and pulmonary circuits is true? a. The blood flow is greater through the systemic. b. The blood flow is greater through the pulmonary. c. The absolute pressure is higher in the pulmonary. d. The blood flow is the same in both. e. The pressure gradient is the same in both.

d. Pressures are higher in the systemic circuit, but because the cardiovascular system is a closed loop, the flow must be the same in both

11. Which of the following would help restore homeostasis in the first few moments after a person's mean arterial pressure became elevated? a. a decrease in baroreceptor action potential frequency b. a decrease in action potential frequency along parasympathetic neurons to the heart c. an increase in action potential frequency along sympathetic neurons to the heart d. a decrease in action potential frequency along sympathetic neurons to arterioles e. an increase in total peripheral resistance

d. Reduced firing to arterioles would reduce total peripheral resistance and thereby reduce mean arterial pressure toward normal.

10. Single-unit smooth muscle differs from multiunit smooth muscle because a. single-unit muscle contraction speed is slow, and multiunit is fast. b. single-unit muscle has T-tubules, and multiunit muscle does not. c. single-unit muscles are not innervated by autonomic nerves. d. single-unit muscle contracts when stretched, whereas multiunit muscle does not. e. single-unit muscle does not produce action potentials spontaneously, but multiunit muscle does.

d. Stretching a sheet of single-unit smooth muscle cells opens mechanically gated ion channels, which causes a depolarization that propagates through gap junctions, followed by Ca2+ entry and contraction. This does not occur in multiunit smooth muscle.

6. Considered as a whole, the body's capillaries have a. smaller cross-sectional area than the arteries. b. less total blood flow than in the veins. c. greater total resistance than the arterioles. d. slower blood velocity than in the arteries. e. greater total blood flow than in the arteries

d. The large total cross-sectional area of capillaries results in very slow blood velocity.

If a patient suffers a stroke that destroys the optic tract on the right side of the brain, which of the following visual defects will result? a. Complete blindness will result. b. There will be no vision in the left eye, but vision will be normal in the right eye. c. The patient will not perceive images of objects striking the left half of the retina in the left eye. d. The patient will not perceive images of objects striking the right half of the retina in the right eye. e. Neither eye will perceive objects in the right side of the patient's field of view.

d. When the right optic tract is destroyed, perception of images formed on the right half of the retina in both eyes is lost, so nothing is visible at the left side of a person's field of view.

4. If other factors are equal, which of the following vessels would have the lowest resistance? a. length = 1 cm, radius = 1 cm b. length = 4 cm, radius = 1 cm c. length = 8 cm, radius = 1 cm d. length = 1 cm, radius = 2 cm e. length = 0.5 cm, radius = 2 cm

e. Resistance decreases as the fourth power of an increase in radius, and in direct proportion to a decrease in vessel length.

Which type of receptor does not encode a somatic sensation? a. muscle-spindle stretch receptor b. nociceptor c. Pacinian corpuscle d. thermoreceptor e. cochlear hair cell

e. Somatic sensations include those from the skin, muscles, bones, tendons, and joints, but not encoding of sound by cochlear hair cells.

11. Which of the following describes a similarity between cardiac and smooth muscle cells? a. An action potential always precedes contraction. b. The majority of the Ca2+ that activates contraction comes from the extracellular fluid. c. Action potentials are generated by slow waves. d. An extensive system of T-tubules is present. e. Ca2+ release and contraction strengths are graded.

e. The amount of Ca2+ released during a typical resting heartbeat exposes less than half of the thin filament cross-bridge binding sites. Autonomic neurotransmitters and hormones can increase or decrease the amount of Ca2+ released to the cytosol during EC coupling, producing a graded contraction as occurs in smooth muscle.

2. Which is correct regarding a skeletal muscle sarcomere? a. M lines are found in the center of the I band. b. The I band is the space between one Z line and the next. c. The H zone is the region where thick and thin filaments overlap. d. Z lines are found in the center of the A band. e. The width of the A band is equal to the length of a thick filament.

e. The dark stripe in a striated muscle that constitutes the A band results from the aligned thick filaments within myofibrils, so thick filament length is equal to A-band width.

12. Which is false about L-type Ca2+ channels in cardiac ventricular muscle cells? a. They are open during the plateau of the action potential. b. They allow Ca2+ entry that triggers sarcoplasmic reticulum Ca2+ release. c. They are found in the T-tubule membrane. d. They open in response to depolarization of the membrane. e. They contribute to the pacemaker potential.

e. Ventricular muscle cells do not have a pacemaker potential, and the L-type Ca2+ channel is not open during this phase of the action potential even in autorhythmic cells.

15. Which is not part of the cascade leading to formation of a blood clot? a. contact between the blood and collagen found outside the blood vessels b. prothrombin converted to thrombin c. formation of a stabilized fibrin mesh d. activated platelets e. secretion of tissue plasminogen activator (t-PA) by endothelial cells

e. t-PA is part of the fibrinolytic system that dissolves clots

Which best describes the vision of a person with uncorrected nearsightedness? a. The eyeball is too long; far objects focus on the retina when the ciliary muscle contracts. b. The eyeball is too long; near objects focus on the retina when the ciliary muscle i relaxed. c. The eyeball is too long; near objects cannot be focused on the retina. d. The eyeball is too short; far objects cannot be focused on the retina. e. The eyeball is too short; near objects focus on the retina when the ciliary muscle is relaxed.

b. A myopic (nearsighted) person has an eyeball that is too long. When the ciliary muscles are relaxed and the lens is as flat as possible, parallel light rays from distant objects focus in front of the retina, whereas diverging rays from near objects are able to focus on the retina. (Recall that with normal vision, it takes ciliary muscle contraction and a rounded lens to focus on near objects.)

3. When a skeletal muscle fiber undergoes a concentric isotonic contraction, a. M lines remain the same distance apart. b. Z lines move closer to the ends of the A bands. c. A bands become shorter. d. I bands become wider. e. M lines move closer to the end of the A band.

b. As filaments slide during a shortening contraction, the I band becomes narrower, so the distance between the Z line and the thick filaments (at the end of the A band) must decrease.

6. What prevents a drop in muscle fiber ATP concentration during the first few seconds of intense contraction? a. Because cross-bridges are pre-energized, ATP is not needed until several cross-bridge cycles have been completed. b. ADP is rapidly converted back to ATP by creatine phosphate. c. Glucose is metabolized in glycolysis, producing large quantities of ATP. d. The mitochondria immediately begin oxidative phosphorylation. e. Fatty acids are rapidly converted to ATP by oxidative glycolysis.

b. In the first few seconds of exercise, mass action favors transfer of the high-energy phosphate from creatine phosphate to ADP by the enzyme creatine kinase.

Using a single intracellular recording electrode, in what part of a sensory neuron could you simultaneously record both receptor potentials and action potentials? a. in the cell body b. at the node of Ranvier nearest the peripheral end c. at the axon hillock where the axon meets the cell body d. at the central axon terminals within the CNS e. There is no single point where both can be measured.

b. Receptor potentials generate only local currents in the receptor membrane that transduces the stimulus, but when they reach the first node of Ranvier, they depolarize the membrane to threshold, and there the voltage-gated Na+ channels first initiate action potentials. Beyond that point, the receptor potential decreases with distance, whereas action potentials propagate all the way to the central axon terminals.

1. Hematocrit is increased a. when a person has a vitamin B12 deficiency. b. by an increase in secretion of erythropoietin. c. when the number of white blood cells is increased. d. by a hemorrhage. e. in response to excess oxygen delivery to the kidneys.

b. Reduced oxygen delivery to the kidneys increases the secretion of erythropoietin, which stimulates bone marrow to increase production of erythrocytes

9. what is mainly responsible for the delay between the atrial and ventricular contractions? a. the shallow slope of AV node pacemaker potentials b. slow action potential conduction velocity of AV node cells c. slow action potential conduction velocity along atrial muscle cell membranes d. slow action potential conduction in the Purkinje network of the ventricles e. greater parasympathetic nerve firing to the ventricles than to the atria

b. The AV node is the only conduction point between atria and ventricles, and the slow propagation through it delays the beginning of ventricular contraction.

8. What is the mean arterial pressure in a person with a systolic pressure of 160 mmHg and a diastolic pressure of 100 mmHg? Hint: See Figure 12.34a.

120 mmHg. MAP = DP + 1/3 (SP − DP)

How does the sensory transduction mechanism in the vestibular and auditory systems demonstrate the importance of the general principle of physiology that controlled exchange of materials occurs between compartments and across cellular membranes?

A good example of the importance of controlled exchange between extracellular compartments in the vestibular and auditory systems is the endolymph found within the cochlear duct and vestibular apparatus. The unusually high K+ concentration allows current to flow into the cells when tip links are stretched, generating a receptor potential that leads to neurotransmitter release from the hair cells. This, in turn, generates action potentials in the afferent neuron (review Figure 7.41). In addition, like in all neurons and excitable cells, the maintenance of Na+ and K+ concentration gradients between the intracellular and extracellular fluid compartments by Na+/K+-ATPase pumps is essential for the transmission of action potentials in the auditory and vestibular afferent neurons (

2. Which would cause a greater increase in resistance to flow, a doubling of blood viscosity or a halving of tube radius? Hint: See equation 12-2 in Section 12.2.

A halving of tube radius. Resistance is directly proportional to blood viscosity but inversely proportional to the fourth power of tube radius.

11. A person is accumulating edema throughout the body. Average capillary pressure is 25 mmHg, and lymphatic function is normal. What is the most likely cause of the edema? Hint: See Figure 12.45

A low plasma protein concentration. Capillary pressure is, if anything, lower than normal and so cannot be causing the edema. Another possibility is that capillary permeability to plasma proteins has increased, as occurs in burns

4. Hypertonia is usually considered a sign of disease of the descending motor pathways. How might it also result from abnormal function of the alpha motor neurons? Hint: Think about inhibitory synapses

A toxin that interferes with the inhibitory synapses on motor neurons would leave unbalanced the normal excitatory input to these neurons. Thus, the otherwise normal motor neurons would fire excessively, which would result in increased muscle contraction. This is exactly what happens in lockjaw as a result of the toxin produced by the tetanus bacillus.

How could the concept of referred pain potentially complicate the clinical assessment of the source of a patient's somatic pain?

Because it is common for somatic receptors in visceral organs to converge onto ascending pathways for receptors in the skin, muscles, and joints (see Figure 7.17), physicians must be aware that complaints about pain in superficial structures may indicate a deeper problem. For example, a person having a heart attack may complain of pain in the left arm, a patient with stomach cancer may experience pain in the middle of the back, and a patient with kidney stones may complain of an ache in the upper thigh or hip. Review Figure 7.18 for a map of surface regions of the body where referred pain from deeper organs can be perceived.

7. A patient is taking a drug that blocks beta-adrenergic receptors. What changes in cardiac function will the drug cause? Hint: See Figure 12.29 and Table 12.5 and think about the effect of these receptors on heart rate and contractilit

Decreased heart rate and contractility. These are effects mediated by the sympathetic nerves on beta-adrenergic receptors in the heart

8. Some endocrine tumors secrete a hormone that leads to elevation of extracellular fluid Ca2+ concentrations. How might this affect cardiac muscle? Hint: Think about Ca2+ channels and the relationship between Ca2+ and depolarization in cardiac muscle cells.

Elevation of extracellular fluid Ca2+ concentration would increase the amount of Ca2+ entering the cytosol through L-type Ca2+ channels. This would result in a greater depolarization of cardiac muscle cell membranes during action potentials. The strength of cardiac muscle contractions would also be increased because this larger Ca2+ entry would trigger more Ca2+ release through ryanodine receptor channels, and consequently there would be a greater activation of cross-bridge cycling.

9. In patients with Parkinson's disease, an excess of dopamine from neurons of the substantia nigra causes intention tremors when the person performs voluntary movements.

F. In Parkinson's disease, a deficit of dopamine from neurons of the substantia nigra results in "resting tremors."

8. Neurons descending in the corticospinal pathway control mainly trunk musculature and postural reflexes, whereas neurons of the brainstem pathways control fine motor movements of the distal extremities.

F. The reverse is actually true

7. Patients with upper motor neuron disorders generally have reduced muscle tone and flaccid paralysis.

F. Upper motor neuron disorders are typically characterized by hypertonia and spasticity.

1. A general principle of physiology states that information flow between cells, tissues, and organs is an essential feature of homeostasis and allows for integration of physiological processes. How is this principle demonstrated by the relationship between the circulatory and endocrine systems?

Hormones of the endocrine system represent vital information that integrates the function of cells and organs that are widely distributed in the body. The circulatory system delivers blood and any hormones it may contain rapidly and efficiently to all cells throughout the body. Without this information-delivery system, the endocrine system could not function properly in the regulation of homeostasis.

18. The P wave records the spread of depolarization of the atria on a lead I ECG as an upright wave form. Referring to the orientation of the ECG leads in Figure 12.18, what difference in the shape of the P wave might you expect when recording with lead aVR? Hint: See Figures 12.18 and 12.19.

In lead aVR, the electrical poles of the leads are oriented nearly the opposite of lead 1: Lead 1 is a vector oriented from the right side of the body toward a positive pole on the left arm, while lead aVR is a vector oriented from the left side of the body toward a positive pole on the right arm. Thus, if the sweep of depolarization toward the positive pole in lead 1 generates an upright P wave, you can expect that same sweep of depolarization away from the positive pole in lead aVR to produce a downward P wave.

5. What neurotransmitters/receptors might be effective targets for drugs used to prevent the muscle spasms characteristic of the disease tetanus

In mild cases of tetanus, agonists (stimulators) of the inhibitory interneuron neurotransmitter gamma-aminobutyric acid (GABA) can shift the balance back toward the inhibition of alpha motor neurons. In more severe cases, paralysis can be induced by administering long-lasting drugs that block the nicotinic acetylcholine receptors at the neuromuscular junction.

9. If a single twitch of a skeletal muscle fiber lasts 40 msec, what action potential stimulation frequency (in action potentials per second) must be exceeded to produce an unfused tetanus?

In order for unfused tetanus to occur, action potentials must occur more closely in time than the duration of a twitch cycle. Frequency is the inverse of cycle duration, so to produce unfused tetanus, action potentials must occur at a frequency greater than 1/0.04 seconds, or 25 action potentials per second.

7. In the laboratory, if an isolated skeletal muscle is placed in a solution that contains no calcium ions, will the muscle contract when it is stimulated (a) directly by depolarizing its membrane, or (b) by stimulating the nerve to the muscle? What would happen if it was a smooth muscle?

In the absence of extracellular Ca2+, skeletal muscle contracts normally in response to an action potential generated in its plasma membrane because the Ca2+ required to trigger contraction comes entirely from the sarcoplasmic reticulum within the muscle fibers. If the motor neuron to the muscle is stimulated in a Ca2+-free medium, however, the muscle will not contract because the influx of Ca2+ from the extracellular fluid into the motor nerve terminal is necessary to trigger the release of acetylcholine that in turn triggers an action potential in the muscle. In a Ca2+-free solution, smooth muscles would not respond either to stimulation of the nerve or to the plasma membrane. Stimulating the nerve would have no effect because Ca2+ entry into presynaptic terminals is necessary for neurotransmitter release. Stimulating the smooth muscle cell membrane would also not cause a response in the absence of Ca2+ because in all of the various types of smooth muscle, Ca2+ must enter from outside the cell to trigger contraction. In some cases, the external Ca2+ directly initiates contraction, and in others it triggers the release of Ca2+ from the sarcoplasmic reticulum (Ca2+-induced Ca2+ release).

At what two sites would central nervous system injuries interfere with the perception that heat is being applied to the right side of the body? At what single site would a central nervous system injury interfere with the perception that heat is being applied to either side of the body?

Information regarding temperature is carried via the anterolateral system to the brain. Fibers of this system cross to the opposite side of the body in the spinal cord at the level of entry of the afferent fibers (see Figure 7.20a). Damage to the left side of the spinal cord or any part of the left side of the brain that contains fibers of the pathways for temperature would interfere with awareness of a heat stimulus on the right. Thus, damage to the somatosensory cortex of the left cerebral hemisphere (i.e., opposite the stimulus) would interfere with awareness of the stimulus. Injury to the spinal cord at the point at which fibers of the anterolateral system from the two halves of the spinal cord cross to the opposite side would interfere with the awareness of heat applied to either side of the body, as would the unlikely event that damage occurred to relevant areas of both sides of the brain.

15. What happens to the hematocrit within several hours after a hemorrhage? Hint: See Table 12.9 and remember what happens to interstitial fluid volume

It decreases. The hemorrhage causes no immediate change in hematocrit because erythrocytes and plasma are lost in the same proportion. As interstitial fluid starts entering the capillaries, however, it expands the plasma volume and decreases hematocrit. (This is too soon for any new erythrocytes to be synthesized.)

14. When the afferent nerves from all the arterial baroreceptors are cut in an experimental animal, what happens to mean arterial pressure? Hint: What will the brain "think" the arterial pressure is

It increases. There are a certain number of impulses traveling up the nerves from the arterial baroreceptors. When these nerves are cut, the number of impulses reaching the medullary cardiovascular center goes to zero, just as it would physiologically if the mean arterial pressure were to decrease markedly. Accordingly, the medullary cardiovascular center responds to the absent impulses by reflexively increasing arterial pressure.

13. The following data are obtained for an experimental animal before and after administration of a drug. Before: Heart rate = 80 beats/min; Stroke volume = 80 mL/beat After: Heart rate = 100 beats/min; Stroke volume = 64 mL/beat Total peripheral resistance remains unchanged. What has the drug done to mean arterial pressure? Hint: Recall the relationship between heart rate, stroke volume, and cardiac output.

Nothing. Cardiac output and TPR have remained unchanged, so their product, MAP, also remains unchanged. This question emphasizes that MAP depends on cardiac output but not on the combination of heart rate and stroke volume that produces the cardiac output

2. Another general principle of physiology is that homeostasis is essential for health and survival. How might the withdrawal reflex (see Figure 10.8) contribute to the maintenance of homeostasis?

One way that the withdrawal reflex contributes to homeostasis is by minimizing the extent of tissue injury that could potentially result from prolongation of a painful stimulus. Rapidly withdrawing a limb from a position where it is being cut, burned, or crushed helps to minimize the loss of blood, tissue fluid, and tissue function that could compromise homeostasis.

4. A person with a heart rate of 40 has no P waves but normal QRS complexes on the ECG. What is the explanation? Hint: See Figures 12.19 and 12.22 and remember the source of the P wave.

The SA node is not functioning, and the ventricles are being driven by a pacemaker in the AV node or the bundle of His.

1. Some cardiac muscle cells are specialized to serve as pacemaker cells that generate action potentials at regular intervals. Stimulation by sympathetic neurotransmitters increases the frequency of action potentials generated, while parasympathetic stimulation reduces the frequency. Which of the general principles of physiology described in Chapter 1 does this best demonstrate?

The control of cardiac muscle pacemaker cell activity by sympathetic and parasympathetic neurotransmitters is an excellent example of the general principle that most physiological functions are controlled by multiple regulatory systems, often working in opposition.

3. Explain how the process of skeletal muscle excitation-contraction coupling demonstrates the general principle of physiology that controlled exchange of materials occurs between compartments and across cellular membranes.

The general principle that controlled exchange of materials occurs between compartments and across cellular membranes is demonstrated by the movements of Ca2+ and other ions involved in the skeletal muscle excitation-contraction coupling mechanism (see Figures 9.9 and 9.12). Controlled movement of Na+, K+, and Ca2+ across muscle cell plasma membranes maintains the resting membrane potential and allows the generation and propagation of action potentials. Sequestering Ca2+ in the sarcoplasmic reticulum allows the resting state of muscle to be maintained until controlled release of Ca2+ into the cytosol activates cross-bridge cycling and muscle contraction. The termination of muscle contraction requires the return of Ca2+ into the sarcoplasmic reticulum and extracellular fluid. This principle is also demonstrated by ion fluxes in cardiac muscle (see Figure 9.40).

2. When a small load is attached to a skeletal muscle that is then tetanically stimulated, the muscle lifts the load in an isotonic contraction over a certain distance but then stops shortening and enters a state of isometric contraction. With a heavier load, the distance shortened before entering an isometric contraction is shorter. Explain these shortening limits in terms of the length-tension relation of muscle.

The length-tension relationship states that the maximum tension developed by a muscle decreases at lengths below L0. During normal shortening, as the sarcomere length becomes shorter than the optimal length, the maximum tension that can be generated decreases. With a light load, the muscle will continue to shorten until its maximal tension just equals the load. No further shortening is possible because at shorter sarcomere lengths the tension would be less than the load. The heavier the load, the less the distance shortened before reaching the isometric state.

3. Two of the body's important fluid compartments are those of the interstitial fluid and plasma. How does the liver's production of plasma proteins interact with those compartments to illustrate the general principle of physiology, Controlled exchange of materials occurs between compartments and across cellular membranes?

The liver produces plasma proteins at a rate that keeps their concentration in the plasma within a narrow range. Plasma proteins do not freely exchange across capillary walls, and their concentration determines the value of πC, the main force that opposes bulk flow of fluid from the plasma to the interstitial fluid (see Figure 12.45). Maintaining balance in the bulk flow forces is essential for controlling the movement of fluid between the interstitial and plasma compartments. The failure of the liver to maintain plasma protein concentration in individuals who are protein starved (kwashiorkor) or who have hepatic damage results in excessive filtration of fluid from the plasma and tissue edema.

5. If the blood flow to a skeletal muscle were markedly decreased, which types of motor units would most rapidly undergo a severe reduction in their ability to produce ATP for muscle contraction? Why?

The oxidative motor units, both fast and slow, will be affected first by a decrease in blood flow because they depend on blood flow to provide both the fuel—glucose and fatty acids—and the oxygen required to metabolize the fuel. The fast-glycolytic motor units will be affected more slowly because they rely predominantly on internal stores of glycogen, which is anaerobically metabolized by glycolysis

19. Given the following cardiac performance data, Cardiac output (CO) = 5400 mL/min Heart rate (HR) = 75 beats/min End-systolic volume (ESV) = 60 mL calculate the ejection fraction (EF). Hint: See Figure 12.22 and the description of ejection fraction associated with Figure 12.28.

The stroke volume can be determined by inserting cardiac output and heart rate into the equation CO = HR × SV: 5400 mL/ min = 75 beats/min × SV; so SV = 72 mL. Next, the enddiastolic volume (EDV) can be determined using the equation SV = EDV − ESV: 72 mL = EDV − 60; so EDV = 132 mL. Finally, the ejection fraction (EF) is EF = SV/EDV, so EF = 72 mL/132 mL = 54.5%.

6. A person has a left atrial pressure of 20 mmHg and a left ventricular pressure of 5 mmHg during ventricular filling. What is the explanation? Hint: See Figures 12.21 and 12.22

This question is analogous to question 12.5 in that the large pressure difference across a valve while the valve is open indicates an abnormally narrowed valve—in this case, the left AV valve.

17. When a heart is transplanted into a patient, it is not possible to connect autonomic neurons from the medullary cardiovascular centers to the new heart. Will such a patient be able to increase cardiac output during exercise? Hint: Recall the effects of circulating catecholamines and changes in venous return on cardiac output.

Transplant recipients can increase cardiac output during exercise in two ways. When exercise begins, epinephrine is released from the adrenal medulla and stimulates β-adrenergic receptors on the heart. This increases heart rate and contractility just like would happen in response to norepinephrine released directly from sympathetic neurons; only the response will be delayed in onset. Also, when the individual starts to exercise and venous return to the heart is increased, end-diastolic volume is increased. This initiates the Frank-Starling mechanism, increasing stroke volume and contributing to an increased cardiac output.

What would vision be like after a drug has destroyed all the cones in the retina? Hint: Think about more than just color.

Vision would be restricted to the rods; therefore, it would be normal at very low levels of illumination (when the cones would not be stimulated anyway). At higher levels of illumination, however, clear vision of fine details would be lost, particularly from the center of the visual field where cones are concentrated, and everything would appear in shades of gray, with no color vision. In very bright light, there would be no vision because of bleaching of the rods' rhodopsin.

5. Why is the latent period longer during an isotonic twitch of a skeletal muscle fiber than it is during an isometric twitch? a. Excitation-contraction coupling is slower during an isotonic twitch. b. Action potentials propagate more slowly when the fiber is shortening, so extra time is required to activate the entire fiber. c. In addition to the time for excitation-contraction coupling, it takes extra time for enough cross-bridges to attach to make the tension in the muscle fiber greater than the load. d. Fatigue sets in much more quickly during isotonic contractions, and when muscles are fatigued the cross-bridges move much more slowly. e. The latent period is longer because isotonic twitches only occur in slow (type I) muscle fibers.

c. In an isometric twitch, tension begins to rise as soon as excitation- contraction is complete and the first cross-bridges begin to attach. In an isotonic twitch, excitation-contraction coupling takes the same amount of time, but the fiber is delayed from shortening until after enough cross-bridges have attached to move the load.

8. Which is true regarding the structure of smooth muscle? a. The thin filament includes the regulatory protein troponin. b. The thick and thin filaments are organized in sarcomeres. c. Thin filaments are anchored to dense bodies instead of Z lines. d. The cells have multiple nuclei. e. Single-unit smooth muscles do not have gap junctions connecting individual cells

c. In smooth muscle cells, dense bodies serve the same functional role as Z lines do in striated muscle cells—they serve as the anchoring point for the thin filaments.

10. Which of the following pressures is closest to the mean arterial blood pressure in a person whose systolic blood pressure is 135 mmHg and pulse pressure is 50 mmHg? a. 110 mmHg b. 78 mmHg c. 102 mmHg d. 152 mmHg e. 85 mmHg

c. The diastolic pressure in this example is 85; adding 1/3 of the pulse pressure gives a MAP of 101.7 mmHg.

2. In the stretch reflex, a. Golgi tendon organs activate contraction in extrafusal muscle fibers connected to that tendon. b. lengthening of muscle-spindle receptors in a muscle leads to contraction in an antagonist muscle. c. action potentials from muscle-spindle receptors in a muscle form monosynaptic excitatory synapses on motor neurons to extrafusal fibers within the same muscles. d. slackening of intrafusal fibers within a muscle activates gamma motor neurons that form excitatory synapses with extrafusal fibers within that same muscle. e. afferent neurons to the sensorimotor cortex stimulate the agonist muscle to contract and the antagonist muscle to be inhibited.

c. When a given muscle is stretched, muscle-spindle stretch receptors send action potentials along afferent fibers that synapse directly on alpha motor neurons to extrafusal fibers to that muscle, causing it to contract back toward the prestretched length.

A standing subject looking over her left shoulder suddenly rotates her head to look over her right shoulder. How does the vestibular system detect this motion? a. The utricle goes from a vertical to a horizontal position, and otoliths stimulate stereocilia. b. Stretch receptors in neck muscles send action potentials to the vestibular apparatus, which relays them to the brain. c. Fluid within the semicircular canals remains stationary, bending the cupula and stereocilia as the head rotates. d. The movement causes endolymph in the cochlea to rotate from right to left, stimulating inner hair cells. e. Counterrotation of the aqueous humor activates a nystagmus response.

c. With the sudden head rotation from left to right, inertia of the endolymph causes it to rotate from right to left with respect to the semicircular canal that lies in the horizontal plane. This fluid flow bends the cupula and embedded hair cells within the ampulla, which influences the firing of action potentials along the vestibular nerve.