Unit 2 -q&a

Question 1

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

Answer 1

Do not require adenosine triphosphate (ATP)

Question 2

What is the osmolarity of a solution containing 10
millimolar NaCl, 5 millimolar KCl, and 10 millimolar
CaCl2 (in mOsm/L)?

Answer 2

100

Question 3

Which of the following best describes the equilibrium
potential for Cl− (in millivolts)?

Answer 3

−85

Question 4

Which of the following best describes the equilibrium
potential for K+ (in millivolts)?

Answer 4

−88

Question 5

The net driving force is greatest for which ion when the membrane potential of this cell is −85 millivolts?

Answer 5

Ca++

Question 6

If this cell were permeable only to K+, what would be
the effect of reducing the extracellular K+ concentration from 5 to 2.5 millimolar?

Answer 6

19 millivolts hyperpolarization

Question 7

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?

Answer 7

Shrink, then return to original volume

Question 8

A clinical study is conducted to determine the actions
of an unknown test solution on red blood cell volume.
One milliliter of heparinized human blood is pipetted
into 100 milliliters of test solution and mixed. Samples are taken and analyzed immediately before and at 1-second intervals after mixing.

The results show that red blood cells placed into the test solution immediately swell and burst. Which of the following best describes the tonicity and osmolarity of the test solution?

Answer 8

Hypotonic; could be hyperosmotic, hypo-osmotic,
or iso-osmotic

Question 9

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

Answer 9

Removal of sarcoplasmic Ca++

Question 10

A model cell with three different transporters (X, Y, and Z) and a resting membrane potential of −75 millivolts is shown in the above figure. Consider the intracellular and extracellular concentrations of all three ions to be typical of a normal cell.

Which of the following best
describes transporter Y?

Answer 10

Secondary active transport

Question 11

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

Answer 11

Contracts in response to stretch

Question 12

The resting potential of a myelinated nerve fiber is
primarily dependent on the concentration gradient of which of the following ions?

Answer 12

K+

Question 13

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

Answer 13

Troponin C

Question 14

In the figure below, two compartments (X and Y) are
separated by a typical biological membrane (lipid bilayer).

The concentrations of glucose in compartments X
and Y at time zero are shown. There are no transporters for glucose in the membrane, and the membrane is impermeable to glucose. Which of the figures best represent the volumes of compartments X and Y when the system reaches equilibrium?

Answer 14

B

Question 15

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?

Answer 15

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

Question 16

A neurotransmitter activates its receptor on an ion
channel of a neuron, which causes the water-filled
channel to open. Once the channel is open, ions move through the channel down their respective electrochemical gradients. A change in membrane potential follows. Which of the following best describes the type of channel and mechanism of ion transport?

Answer 16

Ligand gated

Simple diffusion

Question 17

A 55-year-old woman has a serum potassium of 6.1
mEq/L (normal: 3.5-5.0 mEq/L) and a serum sodium
of 150 mEq/L (normal: 135-147 mEq/L). Which of the
following sets of changes best describe the K+ Nernst
potential and resting membrane potential in a typical
neuron in this woman compared to normal? (Assume
normal intracellular ion concentrations.)

Answer 17

K+ Nernst Potential is Less negative

Resting Membrane Potential is
Less negative

Question 18

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

Answer 18

I band of the sarcomere

Question 19

Equilibrium potentials for three unknown ions are
shown in the above figure. Note that ions S and R
are positively charged and that ion Q is negatively
charged. Assume that the cell membrane is permeable to all three ions and that the cell has a resting membrane potential of −90 millivolts. Which of the following best describes the net movement of the various ions across the cell membrane by passive diffusion?

Answer 19

Outward

Inward

Inward

Question 20

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

Answer 20

Ca++

Question 21

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

Answer 21

Hypertrophy of individual muscle fibers

Question 22

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

Answer 22

E (big)

Question 23

Five hypothetical nerve axons are shown in the above figure. Axons A and B are myelinated, whereas axons C, D, and E are non-myelinated.

Which axon is most likely to have the fastest conduction velocity for an action potential?

Answer 23

B

Question 24

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

Answer 24

Movement of Na+ into the cell

Question 25

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

Answer 25

Movement of K+ out of the cell

Question 26

The axon of a neuron is stimulated experimentally with a 25-millivolt pulse, which initiates an action potential with a velocity of 50 meters per second. The axon is then stimulated with a 100-millivolt pulse.

What is the action potential velocity after the 100-millivolt stimulation pulse (in meters per second)?

Answer 26

100

Question 27

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?

Answer 27

Slower cycling rate of the smooth muscle myosin cross-bridges

Question 28

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 precontracted with acetylcholine. Which of the following mechanisms
of action is most likely to induce this effect?

Answer 28

Stimulation of adenylate cyclase

Question 29

Which of the following best describes muscle B compared with muscle A?

Answer 29

Innervated by smaller nerve fibers

Question 30

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 the following
events to occur?

Answer 30

Ca++ to accumulate in the sarcoplasm

Question 31

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

Answer 31

Levels of ACh at the muscle end plates

Question 32

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

Answer 32

Autoimmune response

Question 33

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

Answer 33

Neostigmine

Question 34

The figure above shows a relationship between contraction velocity and force for five different skeletal muscles. Which of the following muscles (A-E) is most likely to correspond to muscle number 1 on the figure shown? (Assume that all muscles shown are at their normal resting lengths.)

Answer 34

E

Question 35

the isometric length-tension relationship in a representative intact skeletal muscle:

So-called “active” or contraction-dependent tension

Answer 35

B

Question 36

the isometric length-tension relationship in a representative intact skeletal muscle:

The muscle length at which active tension is maximal

Answer 36

E

Question 37

the isometric length-tension relationship in a representative intact skeletal muscle:

The contribution of noncontractile muscle elements to total tension

Answer 37

C

Question 38

Smooth muscle contraction is terminated by which of
the following?

Answer 38

Dephosphorylation of myosin light chain

Question 39

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

Answer 39

Impaired presynaptic voltage-sensitive Ca++ influx

Question 40

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

Answer 40

Antibodies against the voltage-sensitive Ca++ channel

Question 41

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

Answer 41

Botulinum toxin

Question 42

Point at which the membrane potential (Vm) is closest to the Na+ equilibrium potential

Answer 42

D

Question 43

Point at which the driving force for Na+ is the greatest

Answer 43

F

Question 44

Point at which the ratio of K+ permeability to Na+ permeability (PK/PNa) is the greatest

Answer 44

F

Question 45

A physiology experiment is conducted in which a motoneuron that normally innervates a predominantly fast type II muscle is anastomosed to a predominantly
slow type I muscle. Which of the following is most
likely to decrease in the type I muscle after the transinnervation surgery?

Answer 45

Mitochondrial content

Question 46

In the experiment illustrated in part A of the above
figure, 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). Part B illustrates the fluid distribution across the membranes at equilibration. Assuming complete dissociation, identify each of the solutions shown

Answer 46

1 M glucose 1 M NaCl 1 M CaCl2

Question 47

Trace A best describes the kinetics of which event?

Answer 47

Transport of K+ into a muscle cell

Question 48

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

Answer 48

Transport of O2 across an artificial lipid bilayer

Question 49

Trace A in the above figure 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?

Answer 49

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

Question 50

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

Answer 50

Blockade of voltage-sensitive Na+ channels

Question 51

A 17-year-old soccer player sustained 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?

Answer 51

Temporary reduction in actin and myosin protein synthesis

Question 52

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

Answer 52

Intrinsic pacemaker wave activity

Question 53

Ouabain-sensitive transport of Na+ ions from the cytosol to the extracellular fluid

Answer 53

Primary active transport

Question 54

Glucose uptake into skeletal muscle

Answer 54

Facilitated diffusion

Question 55

Na+-dependent transport of Ca++ from the cytosol to
the extracellular fluid

Answer 55

Counter-transport

Question 56

Transport of glucose from the intestinal lumen into an intestinal epithelial cell

Answer 56

Co-transport

Question 57

Movement of Na+ ions into a nerve cell during the upstroke of an action potential

Answer 57

Simple diffusion

Question 58

Traces A, B, and C in the above figure 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 below that identifies each of the traces

Answer 58

Vm PNa PK

Question 59

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?

Answer 59

3

Question 60

An apparently healthy 15-year-old boy dies during a
minor surgical procedure while under general anesthesia. The boy’s grandfather had also died during a surgical procedure. A clinical assessment team determines that the child had malignant hyperthermia (MH).

MH is an inherited disease in which triggering agents, such as certain anesthetics, stimulate calcium release from storage sites in muscle, leading to elevated concentrations of myoplasmic calcium. The MH crisis is most likely to be associated with which of the following?

Answer 60

Defective ryanodine receptors

Question 61

A 24-year-old woman is admitted as an emergency to
University Hospital after 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 with the preinjured muscle? Assume that series growth of sarcomeres cannot be completed within 6 weeks.

Answer 61

Increase Decrease

Question 62

The length-tension diagram above 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?

Answer 62

55 to 65 grams

Question 63

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?

Answer 63

Myosin light chain phosphatase (MLCP)

Question 64

Which of the following best describes the correct temporal order of events for skeletal muscle?

Answer 64

Nerve action
potential

Muscle action
potential

Muscle
contraction

Question 65

Which of the following best describes a physiological
difference between the contraction of smooth muscle compared with the contraction of cardiac muscle and skeletal muscle?

Answer 65

Does not require an action potential

Question 66

The above figure 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?

Answer 66

Myosin ATPase activity

Question 67

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. He has 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. No evidence of weakness of any other muscles is found. Additional testing indicates the presence of anti-acetylcholine antibodies in the plasma, a normal thyroid function test, and a normal computed tomography scan of the brain and orbit. What is the initial diagnosis?

Answer 67

Juvenile myasthenia gravis