Membrane, Physiology Nerve and Muslce

Question 1

Which of the following best describes the changes in cell volume that will occur when red blood cells (previously equilibrated in a 280-milliosmolar solution of NaCl) are placed in a solution of 140 millimolar NaCl containing 20 millimolar urea, a relatively large but permeant molecule?

A)Cells shrink initially, then swell over time and lyse

B)Cells shrink transiently and return to their original volume over time

C)Cells swell and lyse

D)Cells swell transiently and return to their original volume over time

E)No change in cell volume will occur

Question 2

What is the calculated osmolarity of a solution containing 12 millimolar NaCl, 4 millimolar KCl, and 2 millimolar CaCl2(in mOsm/L)?

A)16

B)26

C)29

D)32

E)38

F)42

Question 3

The table shows the concentrations of four ions across the plasma membrane of a model cell. Refer to this table when answering the following four questions.

3.What is the equilibrium potential for Cl− across the plasma membrane of this cell?

A)0 millivolts

B)122 millivolts

C)−122 millivolts

D)61 millivolts

E)−61 millivolts

4.What is the equilibrium potential for K+ across the plasma membrane of this cell?

A)0 millivolts

B)122 millivolts

C)−122 millivolts

D)61 millivolts

E)−61 millivolts

Question 4

The table shows the concentrations of four ions across the plasma membrane of a model cell. Refer to this table when answering the following four questions.

5.If the membrane potential of this cell is −80 millivolts, the driving force is greatest for which ion?

A)Ca++

B)Cl−

C)K+

D)Na+

6.If this cell were permeable only to K+, what would be the effect of reducing the extracellular K+ concentration from 14 to 1.4 millimolar?

A)10 millivolts depolarization

B)10 millivolts hyperpolarization

C)122 millivolts depolarization

D)122 millivolts hyperpolarization

E)61 millivolts depolarization

F)61 millivolts hyperpolarization

Question 5

The diagram shows the length–tension relationship for a single sarcomere. (Data from Gordon AM, Huxley AF, Julian FJ: The length–tension diagram of single vertebrate striated muscle fibers.J Physiol 171:28P, 1964.) Why is the tension development maximal between points B and C?

A)Actin filaments are overlapping each other

B)Myosin filaments are overlapping each other

C)The myosin filament is at its minimal length

D)The Z discs of the sarcomere abut the ends of the myosin filament

E)There is optimal overlap between the actin and myosin filaments

F)There is minimal overlap between the actin and myosin filaments

Question 6

Simple diffusion and facilitated diffusion share which of the following characteristics?

A)Can be blocked by specific inhibitors

B)Do not require adenosine triphosphate (ATP)

C)Require transport protein

D)Saturation kinetics

E)Transport solute against concentration gradient

Question 7

Excitation–contraction coupling in skeletal muscle involves all of the following events EXCEPT one. Which one is this EXCEPTION?

A)ATP hydrolysis

B)Binding of Ca++ to calmodulin

C) Conformational change in dihydropyridine receptor

D)Depolarization of the transverse tubule (T tubule) membrane

E)Increased Na+ conductance of sarcolemma

Question 8

A single contraction of skeletal muscle is most likely to be terminated by which of the following actions?

A)Closure of the postsynaptic nicotinic acetylcholine receptor

B)Removal of acetylcholine from the neuromuscular junction

C)Removal of Ca++ from the terminal of the motor neuron

D) Removal of sarcoplasmic Ca++

E)Return of the dihydropyridine receptor to its resting conformation

Question 9

Which of the following statements about smooth muscle contraction is most accurate?

A)Ca++independent

B)Does not require an action potential

C)Requires more energy compared to skeletal muscle

D)Shorter in duration compared to skeletal muscle

Question 10

Which of the following best describes an attribute of visceral smooth muscle not shared by skeletal

muscle?

A)Contraction is ATP dependent

B)Contracts in response to stretch

C)Does not contain actin filaments

D)High rate of cross-bridge cycling

E)Low maximal force of contraction

Question 11

The resting potential of a myelinated nerve fiber is primarily dependent on the concentration

gradient of which of the following ions?

A)Ca++

B)Cl−

C)HCO3−

D)K+

E)Na+

Question 12

Calmodulin is most closely related, both structurally and functionally, to which of the following proteins?

A)G-actin

B)Myosin light chain

C)Tropomyosin

D)Troponin C

Question 13

Which of the following is a consequence of myelination in large nerve fibers?

A)Decreased velocity of nerve impulses

B)Generation of action potentials only at the nodes of Ranvier

C)Increased energy requirement to maintain ion gradients

D)Increased membrane capacitance

E)Increased nonselective diffusion of ions across the axon membrane

Question 14

During a demonstration for medical students, a neurologist uses magnetic cortical stimulation to trigger firing of the ulnar nerve in a volunteer. At relatively low-amplitude stimulation, action potentials are recorded only from muscle fibers in the index finger. As the amplitude of the stimulation is increased, action potentials are recorded from muscle fibers in both the index finger and the biceps muscle. What is the fundamental principle underlying this amplitude-dependent response?

A)Large motor neurons that innervate large motor units require a larger depolarizing stimulus

B)Recruitment of multiple motor units requires a larger depolarizing stimulus

C)The biceps muscle is innervated by more motor neurons

D)The motor units in the biceps are smaller than those in the muscles of the fingers

E)The muscles in the fingers are innervated only by the ulnar nerve

Question 15

Similarities between smooth and cardiac muscle include which of the following?

A)Ability to contract in the absence of an action potential

B)Dependence of contraction on Ca++ions

C)Presence of a T tubule network

D)Role of myosin kinase in muscle contraction

E)Striated arrangement of the actin and myosin filaments

Question 16

In a normal, healthy muscle, what occurs as a result of propagation of an action potential to the terminal membrane of a motor neuron?

A)Opening of voltage-gated Ca++ channels in the presynaptic membrane

B)Depolarization of the T tubule membrane follows

C)Always results in muscle contraction

D)Increase in intracellular Ca++ concentration in the motor neuron terminal

E)All of the above are correct

Question 17

Which of the following decreases in length during the contraction of a skeletal muscle fiber?

A)A band of the sarcomere

B)I band of the sarcomere

C)Thick filaments

D)Thin filaments

E)Z discs of the sarcomere

Question 18

A cross-sectional view of a skeletal muscle fiber through the H zone would reveal the presence of what?

A)Actin and titin

B)Actin, but no myosin

C)Actin, myosin, and titin

D)Myosin and actin

E)Myosin, but no actin

Question 19

Tetanic contraction of a skeletal muscle fiber results from a cumulative increase in the intracellular concentration of which of the following?

A)ATP

B)Ca++

C)K+

D)Na+

E)Troponin

Question 20

Malignant hyperthermia is a potentially fatal genetic disorder characterized by a hyper responsiveness to inhaled anesthetics and results in elevated body temperature, skeletal muscle rigidity, and lactic acidosis. Which of the following molecular changes could account for these clinical manifestations?

A)Decreased voltage sensitivity of the dihydropyridine receptor

B)Enhanced activity of the sarcoplasmic reticulum Ca++-ATPase

C)Prolonged opening of the ryanodine receptor channel

D)Reduction in the density of voltage-sensitive Na+channels in the T tubule membrane

Question 21

Weightlifting can result in a dramatic increase in skeletal muscle mass. This increase in muscle mass is primarily attributable to which of the following?

A)Fusion of sarcomeres between adjacent myofibrils

B)Hypertrophy of individual muscle fibers

C)Increase in skeletal muscle blood supply

D)Increase in the number of motor neurons

E)Increase in the number of neuromuscular junctions

Question 22

Which of the following transport mechanisms is not rate limited by an intrinsic Vmax?

A)Facilitated diffusion via carrier proteins

B)Primary active transport via carrier proteins

C)Secondary co-transport

D)Secondary counter-transport

E)Simple diffusion through protein channels

Question 23

Assuming complete dissociation of all solutes, which of the following solutions would be hyperosmotic relative to 1 millimolar NaCl?

A)1 millimolar CaCl2

B)1 millimolar glucose

C)1 millimolar KCl

D)1 millimolar sucrose

E)1.5 millimolar glucose

Question 24

The diagram shows the change in membrane potential during an action potential in a giant squid axon. Refer to it when answering the next two questions.

26. Which of the following is primarily responsible for the change in membrane potential between points B and D?

A) Inhibition of the Na+, K+-ATPase

B)Movement of K+ into the cell

C)Movement of K+ out of the cell

D)Movement of Na+ into the cell

E)Movement of Na+out of the cell

27. Which of the following is primarily responsible for the change in membrane potential between points D and E?

A)Inhibition of the Na+, K+-ATPase

B)Movement of K+into the cell

C)Movement of K+out of the cell

D)Movement of Na+into the cell

E)Movement of Na+ out of the cell

Question 25

The delayed onset and prolonged duration of smooth muscle contraction, as well as the greater force generated by smooth muscle compared with skeletal muscle, are all consequences of which of the following?

A)Greater amount of myosin filaments present in smooth muscle

B)Higher energy requirement of smooth muscle

C)Physical arrangement of actin and myosin filaments

D)Slower cycling rate of the smooth muscle myosin cross-bridges

E)Slower uptake of Ca++ions following contraction

Question 26

An experimental drug is being tested as a potential therapeutic treatment for asthma. Preclinical studies have shown that this drug induces the relaxation of cultured porcine tracheal smooth muscle cells pre-contracted with acetylcholine. Which of the following mechanisms of action is most likely to induce this effect?

A) Decreased affinity of troponin C for Ca++

B)Decreased plasma membrane K+permeability

C)Increased plasma membrane Na+permeability

D)Inhibition of the sarcoplasmic reticulum Ca++-ATPase

E)Stimulation of adenylate cyclase

Question 27

The diagram illustrates the single isometric twitch characteristics of two skeletal muscles, A and B, in response to a depolarizing stimulus. Refer to it when answering the next two questions.

30.Which of the following best describes muscle B, when compared to muscle A?

A)Adapted for rapid contraction

B)Composed of larger muscle fibers

C)Fewer mitochondria

D)Innervated by smaller nerve fibers

E)Less extensive blood supply

31. The delay between the termination of the transient depolarization of the muscle membrane and the onset of muscle contraction observed in both muscles A and B reflects the time necessary for which of thefollowing events to occur?

A)ADP to be released from the myosin head

B)ATP to be synthesized

C)Ca++to accumulate in the sarcoplasm

D)G-actin to polymerize into F-actin

E)Myosin head to complete one cross-bridge cycle

Question 28

A 55-year-old woman visits her physician because of double vision, eyelid droop, difficulty chewing and swallowing, and general weakness in her limbs. All these symptoms are made worse with exercise and occur more frequently late in the day. The physician suspects myasthenia gravis and orders a Tensilon test. The test is positive.

32.The increased muscle strength observed during the Tensilon test is due to an increase in which of the following?

A)Amount of acetylcholine (ACh) released from the motor nerves

B)Levels of ACh at the muscle end-plates

C)Number of ACh receptors on the muscle end-plates

D)Synthesis of norepinephrine

33.What is the most likely basis for the symptoms described in this patient?

A)Autoimmune response

B)Botulinum toxicity

C)Depletion of voltage-gated Ca++ channels in certain motor neurons

D)Development of macro motor units following recovery from poliomyelitis

E)Overexertion

34.Which of the following drugs would likely alleviate this patient’s symptoms?

A)Atropine

B)Botulinum toxin antiserum

C)Curare

D)Halothane

E)Neostigmine

Question 29

The diagrams depict rigid containers composed of two aqueous chambers, A and B, each containing a Na+solution and separated by a Na+-permeable membrane. The panel on the left represents the distribution of Na+ ions at rest in the absence of any electrical potential. In this scenario, the concentration of Na + ions in chamber A equals the concentration of Na+ ions in chamber B ([Na] A= [Na] B). The panel in the right illustrates the effect of a +60-millivolt potential applied across the membrane (chamber B relative to chamber A). Assuming a temperature of 37°C, which of the following expressions best describes the resulting distribution of Na+ ions between the two chambers?

A)[Na]A= 10[Na]B

B)[Na]A= 2[Na]B

C)[Na]A= 60[Na]B

D)[Na]B= 10[Na]A

E)[Na]B= 60[Na]A

Question 30

The diagram illustrates the isometric length-tension relationship in a representative intact skeletal muscle. When answering the following three questions, use the letters in the diagram to identify each of thefollowing.

36. So-called “active” or contraction-dependent tension.
37. The muscle length at which active tension is maximal.
38. The contribution of non-contractile muscle elements to total tension

Question 31

39. Smooth muscle contraction is terminated by which of the following?

A)Dephosphorylation of myosin kinase

B)Dephosphorylation of myosin light chain

C)Efflux of Ca++ions across the plasma membrane

D)Inhibition of myosin phosphatase

E)Uptake of Ca++ions into the sarcoplasmic reticulum

Question 32

A 56-year-old man sees a neurologist because of weakness in his legs that improves over the course of the day or with exercise. Extracellular electrical recordings from a single skeletal muscle fiber reveal normal miniature end-plate potentials. Low-frequency electrical stimulation of the motor neuron, however, elicits an abnormally small depolarization of the muscle fibers. The amplitude of the depolarization is increased after exercise.

40.Based on these findings, which of the following is the most likely cause of this patient’s leg weakness?

A)Acetylcholinesterase deficiency

B)Blockade of postsynaptic acetylcholine receptors

C)Impaired presynaptic voltage-sensitive Ca++influx

D)Inhibition of Ca++re-uptake into the sarcoplasmic reticulum

E)Reduced acetylcholine synthesis

41.A preliminary diagnosis is confirmed by the presence of which of the following?

A)Antibodies against the acetylcholine receptor

B)Antibodies against the voltage-sensitive Ca++channel

C)Mutation in the gene that codes for the ryanodine receptor

D)Relatively few vesicles in the presynaptic terminal

E)Residual acetylcholine in the neuromuscular junction

42.The molecular mechanism underlying these symptoms is most similar to which of the following?

A)Acetylcholine

B)Botulinum toxin

C)Curare

D)Neostigmine

E)Tetrodotoxin

Question 33

Match each of the descriptions to one of the points of the nerve action potential shown in the diagram.

43. Point at which the membrane potential (Vm) is closest to the Na+ equilibrium potential.
44. Point at which the driving force for Na+ is the greatest.
45. Point at which the ratio of K+permeability to Na+ permeability (PK/PNa) is the greatest.

Question 34

ATP is used directly for each of the following processes EXCEPT one. Which one is this EXCEPTION?

A)Accumulation of Ca++ by the sarcoplasmic reticulum

B)Transport of glucose into muscle cells

C)Transport of H+from the parietal cells into the lumen of the stomach

D)Transport of K+from the extracellular to intracellular fluid

E)Transport of Na+ from the intracellular to extracellular fluid

Question 35

In the experiment illustrated in diagram A, equal volumes of solutions X, Y, and Z are placed into the compartments of the two U-shaped vessels shown. The two compartments of each vessel are separated by semipermeable membranes (i.e., impermeable to ions and large polar molecules). Diagram B illustrates the fluid distribution across the membranes at equilibration. Assuming complete dissociation, identify each of the solutions shown.

Question 36

48.The force produced by a single skeletal muscle fiber can be increased by which of the following?

A)Decreasing extracellular K+concentration

B)Increasing the amplitude of the depolarizing stimulus

C)Increasing the frequency of stimulation of the fiber

D)Increasing the number of voltage-gated Na+channels in the sarcolemma

E)Increasing the permeability of the sarcolemma to K

Question 37

49.Trace A best describes the kinetics of which of the following events?

A)Movement of CO2 across the plasma membrane

B)Movement of O2 across a lipid bilayer

C)Na+ flux through an open nicotinic acetylcholine receptor channel

D)Transport of K+ into a muscle cell

E)Voltage-dependent movement of Ca++into the terminal of a motor neuron

50.Trace B best describes the kinetics which of the following events?

A)Na+-dependent transport of glucose into an epithelial cell

B)Transport of Ca++ into the sarcoplasmic reticulum of a smooth muscle cell

C)Transport of K+ into a muscle cell

D)Transport of Na+ out of a nerve cell

E)Transport of O2 across an artificial lipid bilaye

Question 38

51. Trace A represents a typical action potential recorded under control conditions from a normal nerve cell in response to a depolarizing stimulus. Which of the following perturbations would explain the conversion of the response shown in trace A to the action potential shown in trace B?

A)Blockade of voltage-sensitive Na+channels

B)Blockade of voltage-sensitive K+channels

C)Blockade of Na-K “leak” channels

D)Replacement of the voltage-sensitive K+channels with “slow” Ca++ channels

E)Replacement of the voltage-sensitive Na+ channels with “slow” Ca++ channels

52.Which of the following perturbations would account for the failure of the same stimulus to elicit an action potential in trace C?

A)Blockade of voltage-sensitive Na+channels

B)Blockade of voltage-sensitive K+channels

C)Blockade of Na-K “leak” channels

D)Replacement of the voltage-sensitive K+ channels with “slow” Ca++channels

E)Replacement of the voltage-sensitive Na+channels with “slow” Ca++channels

Question 39

53. A 17-year-old soccer player suffered a fracture to the left tibia. After her lower leg has been in a cast for 8 weeks, she is surprised to find that the left gastrocnemius muscle is significantly smaller in circumference than it was before the fracture. What is the most likely explanation?

A)Decrease in the number of individual muscle fibers in the left gastrocnemius

B)Decrease in blood flow to the muscle caused by constriction from the cast

C)Temporary reduction in actin and myosin protein synthesis

D)Increase in glycolytic activity in the affected muscle

E)Progressive denervation

Question 40

Smooth muscle that exhibits rhythmical contraction in the absence of external stimuli also necessarily exhibits which of the following?

A)“Slow” voltage-sensitive Ca++channels

B)Intrinsic pacemaker wave activity

C)Higher resting cytosolic Ca++concentration

D)Hyperpolarized membrane potential

E)Action potentials with “plateaus”

Question 41

A)Simple diffusion

B)Facilitated diffusion

C)Primary active transport

D)Co-transport

E)Counter-transport

Match each of the processes described below with the correct type of transport listed above (each answer may be used more than once).

55. Ouabain-sensitive transport of Na+ions from the cytosol to the extracellular fluid
56. Glucose uptake into skeletal muscle

Question 42

A)Simple diffusion

B)Facilitated diffusion

C)Primary active transport

D)Co-transport

E)Counter-transport

Match each of the processes described below with the correct type of transport listed above (each answer may be used more than once).

57. Na+-dependent transport of Ca++ from the cytosol to the extracellular fluid
58. Transport of glucose from the intestinal lumen into an intestinal epithelial cell
59. Movement of Na+ions into a nerve cell during the upstroke of an action potential

Question 43

Traces A, B, and C in the diagram summarize the changes in membrane potential (Vm) and the underlying membrane permeabilities (P) that occur in a nerve cell over the course of an action potential.

Choose the combination of labels below that accurately identifies each of the traces.

Question 44

If the intracellular concentration of a membrane-permeant substance doubles from 10 to 20 millimolar and the extracellular concentration remains at 5 millimolar, the rate of diffusion of that substance across the plasma membrane will increase by a factor of how much?

A)2

B)3

C)4

D)5

E)6

Question 45

Which of the following pairs of aqueous solutions will exert equal osmotic pressures across a normal cell membrane once steady-state conditions have been established?

Question 46

63. A 12-year-old boy presents with a 4-month history of diminished vision and diplopia. He also experiences tiredness toward the end of the day. There are no other symptoms. On examination, the patient has ptosis of the left eye that improves after a period of sleep. Clinical examination is otherwise normal. There is no evidence of weakness of any other muscles. Additional testing indicates the presence of anti-acetylcholine antibodies in the plasma, a normal thyroid function test, and a normal CT scan of the brain and orbit. What is the initial diagnosis?

A)Astrocytoma

B)Graves disease

C)Hashimoto thyroiditis

D)Juvenile myasthenia gravis

E)Multiple sclerosis

Question 47

The length–tension diagram shown here was obtained from a skeletal muscle with equal numbers of red and white fibers. Supramaximal tetanic stimuli were used to initiate an isometric contraction at each muscle length studied. The resting length was 20 cm. What is the maximum amount of active tension that the muscle is capable of generating at a preload of 100 grams?

A)145–155 grams

B)25–35 grams

C)55–65 grams

D)95–105 grams

E)Cannot be determined

Question 48

The sensitivity of the smooth muscle contractile apparatus to calcium is known to increase in the steady-state under normal conditions. This increase in calcium sensitivity can be attributed to a decrease in the levels of which of the following substances?

A)Actin

B)Adenosine Triphosphate (ATP)

C)Calcium-calmodulin complex

D)Calmodulin

E)Myosin light chain phosphatase (MLCP)

Question 49

The diagram shows the force–velocity relationship for isotonic contractions of skeletal muscle. The differences in the three curves result from differences in which of the following?

A)Frequency of muscle contraction

B)Hypertrophy

C)Muscle mass

D)Myosin ATPase activity

E)Recruitment of motor units

Question 50

A 24-year-old woman is admitted as an emergency to University Hospital following an automobile accident in which severe lacerations to the left wrist severed a major muscle tendon. The severed ends of the tendon were overlapped by 6 cm to facilitate suturing and reattachment. Which of the following would be expected after 6 weeks compared to the preinjured muscle? Assume that series growth of sarcomeres cannot be completed within 6 weeks