Deck 1: Cell Physiology

Question 1

Which of the following characteristics is shared by simple and facilitated diffusion of glucose?

A) Occurs down an electrochemical gradient
B) Is saturable
C) Requires metabolic energy
D) Is inhibited by the presence of galactose
E) Requires a $\mathrm{Na}^{+}$ gradient

Answer 1

Occurs down an electrochemical gradient

Question 2

During the upstroke of the nerve action potential

A) there is net outward current and the cell interior becomes more negative
B) there is net outward current and the cell interior becomes less negative
C) there is net inward current and the cell interior becomes more negative
D) there is net inward current and the cell interior becomes less negative

Answer 2

there is net inward current and the cell interior becomes less negative

Question 3

Solutions A and B are separated by a semipermeable membrane that is permeable to $\mathrm{K}^{+}$ but not to $\mathrm{Cl}^{-}$ . Solution A is $100 \mathrm{mM}$ $\mathrm{KCl}$ , and solution $\mathrm{B}$ is $1 \mathrm{mM} \mathrm{KCl}$ . Which of the following statements about solution A and solution $\mathrm{B}$ is true?

A) $\mathrm{K}^{+}$ ions will diffuse from solution A to solution $B$ until the $\left[\mathrm{K}^{+}\right]$ of both solutions is $50.5 \mathrm{mM}$
B) $\mathrm{K}^{+}$ ions will diffuse from solution $\mathrm{B}$ to solution A until the $\left[\mathrm{K}^{+}\right]$ of both solutions is $50.5 \mathrm{mM}$
C) $\mathrm{KCl}$ will diffuse from solution $\mathrm{A}$ to solution $\mathrm{B}$ until the $[\mathrm{KCl}]$ of both solutions is $50.5 \mathrm{mM}$
D) $\mathrm{K}^{+}$ will diffuse from solution $\mathrm{A}$ to solution B until a membrane potential develops with solution A negative with respect to solution B
E) $\mathrm{K}^{+}$ will diffuse from solution $\mathrm{A}$ to solution B until a membrane potential develops with solution A positive with respect to solution B

Answer 3

$\mathrm{K}^{+}$ will diffuse from solution $\mathrm{A}$ to solution B until a membrane potential develops with solution A negative with respect to solution B

Question 4

The correct temporal sequence for events at the neuromuscular junction is

A) action potential in the motor nerve; depolarization of the muscle end plate; uptake of $\mathrm{Ca}^{2+}$ into the presynaptic nerve terminal
B) uptake of $\mathrm{Ca}^{2+}$ into the presynaptic terminal; release of acetylcholine (ACh); depolarization of the muscle end plate
C) release of ACh; action potential in the motor nerve; action potential in the muscle
D) uptake of $\mathrm{Ca}^{2+}$ into the motor end plate; action potential in the motor end plate; action potential in the muscle
E) release of ACh; action potential in the muscle end plate; action potential in the muscle

Question 5

Which characteristic or component is shared by skeletal muscle and smooth muscle?

A) Thick and thin filaments arranged in sarcomeres
B) Troponin
C) Elevation of intracellular $\left[\mathrm{Ca}^{2+}\right]$ for excitation-contraction coupling
D) Spontaneous depolarization of the membrane potential
E) High degree of electrical coupling between cells

Question 6

Repeated stimulation of a skeletal muscle fiber causes a sustained contraction (tetanus). Accumulation of which solute in intracellular fluid is responsible for the tetanus?

A) $\mathrm{Na}^{+}$
B) $\mathrm{K}^{+}$
C) $\mathrm{Cl}^{-}$
D) $\mathrm{Mg}^{2+}$
E) $\mathrm{Ca}^{2+}$
F) Troponin
G) Calmodulin
H) Adenosine triphosphate (ATP)

Question 7

Solutions A and B are separated by a membrane that is permeable to $\mathrm{Ca}^{2+}$ and impermeable to $\mathrm{Cl}^{-}$ . Solution A contains $10 \mathrm{mM} \mathrm{CaCl}_{2}$ , and solution $\mathrm{B}$ contains $1 \mathrm{mM}$ $\mathrm{CaCl}_{2}$ . Assuming that $2.3 \mathrm{RT} / \mathrm{F}=60 \mathrm{mV}, \mathrm{Ca}^{2+}$ will be at electrochemical equilibrium when

A) solution $\mathrm{A}$ is $+60 \mathrm{mV}$
B) solution $\mathrm{A}$ is $+30 \mathrm{mV}$
C) solution A is $-60 \mathrm{mV}$
D) solution $\mathrm{A}$ is $-30 \mathrm{mV}$
E) solution $\mathrm{A}$ is $+120 \mathrm{mV}$
F) solution $\mathrm{A}$ is $-120 \mathrm{mV}$
G) the $\mathrm{Ca}^{2+}$ concentrations of the two solutions are equal
H) the concentrations of the two solutions are equal

Question 8

A 42-year-old man with myasthenia gravis notes increased muscle strength when he is treated with an acetylcholinesterase (AChE) inhibitor. The basis for his improvement is increased

A) amount of acetylcholine (ACh) released from motor nerves
B) levels of ACh at the muscle end plates
C) number of ACh receptors on the muscle end plates
D) amount of norepinephrine released from motor nerves
E) synthesis of norepinephrine in motor nerves

Question 9

In a hospital error, a 60-year-old woman is infused with large volumes of a solution that causes lysis of her red blood cells (RBCs). The solution was most likely

A) $150 \mathrm{mM} \mathrm{NaCl}$
B) $300 \mathrm{mM}$ mannitol
C) $350 \mathrm{mM}$ mannitol
D) $300 \mathrm{mM}$ urea
E) $150 \mathrm{mM} \mathrm{CaCl}_{2}$

Question 10

During a nerve action potential, a stimulus is delivered as indicated by the arrow shown in the following figure. In response to the stimulus, a second action potential

A) of smaller magnitude will occur
B) of normal magnitude will occur
C) of normal magnitude will occur but will be delayed
D) will occur but will not have an overshoot
E) will not occur

Question 11

Solutions A and B are separated by a membrane that is permeable to urea. Solution A is $10 \mathrm{mM}$ urea, and solution B is $5 \mathrm{mM}$ urea. If the concentration of urea in solution A is doubled, the flux of urea across the membrane will

A) double
B) triple
C) be unchanged
D) decrease to one-half
E) decrease to one-third

Question 12

A muscle cell has an intracellular $\left[\mathrm{Na}^{+}\right]$ of $14 \mathrm{mM}$ and an extracellular $\left[\mathrm{Na}^{+}\right]$ of $140 \mathrm{mM}$ . Assuming that $2.3 \mathrm{RT} / \mathrm{F}=60 \mathrm{mV}$ , what would the membrane potential be if the muscle cell membrane were permeable only to $\mathrm{Na}^{+}$ ?

A) $80 \mathrm{mV}$
B) $-60 \mathrm{mV}$
C) $0 \mathrm{mV}$
D) $+60 \mathrm{mV}$
E) $+80 \mathrm{mV}$

Question 13

The following diagram of a nerve action potential applies to Questions :


-At which labeled point on the action potential is $\mathrm{K}^{+}$ closest to electrochemical equilibrium?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 14

The following diagram of a nerve action potential applies to Questions :


-What process is responsible for the change in membrane potential that occurs between point 1 and point 3 ?

A) Movement of $\mathrm{Na}^{+}$ into the cell
B) Movement of $\mathrm{Na}^{+}$ out of the cell
C) Movement of $\mathrm{K}^{+}$ into the cell
D) Movement of $\mathrm{K}^{+}$ out of the cell
E) Activation of the $\mathrm{Na}^{+}-\mathrm{K}^{+}$ pump
F) Inhibition of the $\mathrm{Na}^{+}-\mathrm{K}^{+}$ pump

Question 15

The following diagram of a nerve action potential applies to Questions :


-What process is responsible for the change in membrane potential that occurs between point 3 and point 4 ?

A) Movement of $\mathrm{Na}^{+}$ into the cell
B) Movement of $\mathrm{Na}^{+}$ out of the cell
C) Movement of $\mathrm{K}^{+}$ into the cell
D) Movement of $\mathrm{K}^{+}$ out of the cell
E) Activation of the $\mathrm{Na}^{+}-\mathrm{K}^{+}$ pump
F) Inhibition of the $\mathrm{Na}^{+}-\mathrm{K}^{+}$ pump

Question 16

The velocity of conduction of action potentials along a nerve will be increased by

A) stimulating the $\mathrm{Na}^{+}-\mathrm{K}^{+}$ pump
B) inhibiting the $\mathrm{Na}^{+}-\mathrm{K}^{+}$ pump
C) decreasing the diameter of the nerve
D) myelinating the nerve
E) lengthening the nerve fiber

Question 17

Solutions A and B are separated by a semipermeable membrane. Solution A contains $1 \mathrm{mM}$ sucrose and $1 \mathrm{mM}$ urea. Solution B contains $1 \mathrm{mM}$ sucrose. The reflection coefficient for sucrose is one, and the reflection coefficient for urea is zero. Which of the following statements about these solutions is correct?

A) Solution A has a higher effective osmotic pressure than solution $B$
B) Solution A has a lower effective osmotic pressure than solution $B$
C) Solutions A and B are isosmotic
D) Solution A is hyperosmotic with respect to solution $\mathrm{B}$ , and the solutions are isotonic
E) Solution A is hyposmotic with respect to solution $\mathrm{B}$ , and the solutions are isotonic

Question 18

Transport of $\mathrm{D}$ - and $\mathrm{L}$ -glucose proceeds at the same rate down an electrochemical gradient by which of the following processes?

A) Simple diffusion
B) Facilitated diffusion
C) Primary active transport
D) Cotransport
E) Countertransport

Question 19

Which of the following will double the permeability of a solute in a lipid bilayer?

A) Doubling the molecular radius of the solute
B) Doubling the oil/water partition coefficient of the solute
C) Doubling the thickness of the bilayer
D) Doubling the concentration difference of the solute across the bilayer

Question 20

A newly developed local anesthetic blocks $\mathrm{Na}^{+}$ channels in nerves. Which of the following effects on the action potential would it be expected to produce?

A) Decrease the rate of rise of the upstroke of the action potential
B) Shorten the absolute refractory period
C) Abolish the hyperpolarizing afterpotential
D) Increase the $\mathrm{Na}^{+}$ equilibrium potential
E) Decrease the $\mathrm{Na}^{+}$ equilibrium potential

Question 21

At the muscle end plate, acetylcholine (ACh) causes the opening of

A) $\mathrm{Na}^{+}$ channels and depolarization toward the $\mathrm{Na}^{+}$ equilibrium potential
B) $\mathrm{K}^{+}$ channels and depolarization toward the $\mathrm{K}^{+}$ equilibrium potential
C) $\mathrm{Ca}^{2+}$ channels and depolarization toward the $\mathrm{Ca}^{2+}$ equilibrium potential
D) $\mathrm{Na}^{+}$ and $\mathrm{K}^{+}$ channels and depolarization to a value halfway between the $\mathrm{Na}^{+}$ and $\mathrm{K}^{+}$ equilibrium potentials
E) $\mathrm{Na}^{+}$ and $\mathrm{K}^{+}$ channels and hyperpolarization to a value halfway between the $\mathrm{Na}^{+}$ and $\mathrm{K}^{+}$ equilibrium potentials

Question 22

An inhibitory postsynaptic potential

A) depolarizes the postsynaptic membrane by opening $\mathrm{Na}^{+}$ channels
B) depolarizes the postsynaptic membrane by opening $\mathrm{K}^{+}$ channels
C) hyperpolarizes the postsynaptic membrane by opening $\mathrm{Ca}^{2+}$ channels
D) hyperpolarizes the postsynaptic membrane by opening $\mathrm{Cl}^{-}$ channels

Question 23

Which of the following would occur as a result of the inhibition of $\mathrm{Na}^{+}, \mathrm{K}^{+}$ -ATPase?

A) Decreased intracellular $\mathrm{Na}^{+}$ concentration
B) Increased intracellular $\mathrm{K}^{+}$ concentration
C) Increased intracellular $\mathrm{Ca}^{2+}$ concentration
D) Increased $\mathrm{Na}^{+}$ -glucose cotransport
E) Increased $\mathrm{Na}^{+}-\mathrm{Ca}^{2+}$ exchange

Question 24

Which of the following temporal sequences is correct for excitationcontraction coupling in skeletal muscle?

A) Increased intracellular $\left[\mathrm{Ca}^{2+}\right]$ ; action potential in the muscle membrane; cross-bridge formation
B) Action potential in the muscle membrane; depolarization of the $\mathrm{T}$ tubules; release of $\mathrm{Ca}^{2+}$ from the sarcoplasmic reticulum (SR)
C) Action potential in the muscle membrane; splitting of adenosine triphosphate (ATP); binding of $\mathrm{Ca}^{2+}$ to troponin C
D) Release of $\mathrm{Ca}^{2+}$ from the SR; depolarization of the $\mathrm{T}$ tubules; binding of $\mathrm{Ca}^{2+}$ to troponin $\mathrm{C}$

Question 25

Which of the following transport processes is involved if transport of glucose from the intestinal lumen into a small intestinal cell is inhibited by abolishing the usual $\mathrm{Na}^{+}$ gradient across the cell membrane?

A) Simple diffusion
B) Facilitated diffusion
C) Primary active transport
D) Cotransport
E) Countertransport

Question 26

In skeletal muscle, which of the following events occurs before depolarization of the T tubules in the mechanism of excitationcontraction coupling?

A) Depolarization of the sarcolemmal membrane
B) Opening of $\mathrm{Ca}^{2+}$ release channels on the sarcoplasmic reticulum (SR)
C) Uptake of $\mathrm{Ca}^{2+}$ into the $\mathrm{SR}$ by $\mathrm{Ca}^{2+}$ adenosine triphosphatase (ATPase)
D) Binding of $\mathrm{Ca}^{2+}$ to troponin $\mathrm{C}$
E) Binding of actin and myosin

Question 27

Adenosine triphosphate (ATP) is used indirectly for which of the following processes?

A) Accumulation of $\mathrm{Ca}^{2+}$ by the sarcoplasmic reticulum (SR)
B) Transport of $\mathrm{Na}^{+}$ from intracellular to extracellular fluid
C) Transport of $\mathrm{K}^{+}$ from extracellular to intracellular fluid
D) Transport of $\mathrm{H}^{+}$ from parietal cells into the lumen of the stomach
E) Absorption of glucose by intestinal epithelial cells

Question 28

Which of the following causes rigor in skeletal muscle?

A) Lack of action potentials in motoneurons
B) An increase in intracellular $\mathrm{Ca}^{2+}$ level
C) A decrease in intracellular $\mathrm{Ca}^{2+}$ level
D) An increase in adenosine triphosphate (ATP) level
E) A decrease in ATP level

Question 29

Degeneration of dopaminergic neurons has been implicated in

A) schizophrenia
B) Parkinson disease
C) myasthenia gravis
D) curare poisoning

Question 30

Assuming complete dissociation of all solutes, which of the following solutions would be hyperosmotic to $1 \mathrm{mM} \mathrm{NaCl}$ ?

A) $1 \mathrm{mM}$ glucose
B) $1.5 \mathrm{mM}$ glucose
C) $1 \mathrm{mM} \mathrm{CaCl}_{2}$
D) $1 \mathrm{mM}$ sucrose
E) $1 \mathrm{mM} \mathrm{KCl}$

Question 31

A new drug is developed that blocks the transporter for $\mathrm{H}^{+}$ secretion in gastric parietal cells. Which of the following transport processes is being inhibited?

A) Simple diffusion
B) Facilitated diffusion
C) Primary active transport
D) Cotransport
E) Countertransport

Question 32

A 56-year-old woman with severe muscle weakness is hospitalized. The only abnormality in her laboratory values is an elevated serum $\mathrm{K}^{+}$ concentration. The elevated serum $\mathrm{K}^{+}$ causes muscle weakness because

A) the resting membrane potential is hyperpolarized
B) the $\mathrm{K}^{+}$ equilibrium potential is hyperpolarized
C) the $\mathrm{Na}^{+}$ equilibrium potential is hyperpolarized
D) $\mathrm{K}^{+}$ channels are closed by depolarization
E) $\mathrm{K}^{+}$ channels are opened by depolarization
F) $\mathrm{Na}^{+}$ channels are closed by depolarization
G) $\mathrm{Na}^{+}$ channels are opened by depolarization

Question 33

In contraction of gastrointestinal smooth muscle, which of the following events occurs after binding of $\mathrm{Ca}^{2+}$ to calmodulin?

A) Depolarization of the sarcolemmal membrane
B) $\mathrm{Ca}^{2+}$ -induced $\mathrm{Ca}^{2+}$ release
C) Increased myosin-light-chain kinase
D) Increased intracellular $\mathrm{Ca}^{2+}$ concentration
E) Opening of ligand-gated $\mathrm{Ca}^{2+}$ channels

Question 34

In an experimental preparation of a nerve axon, membrane potential $\left(\mathrm{E}_{\mathrm{m}}\right), \mathrm{K}^{+}$ equilibrium potential, and $\mathrm{K}^{+}$ conductance can be measured. Which combination of values will create the largest outward current flow?

$\begin{array}{cccc} & \mathrm{E}_{\mathrm{m}}(\mathrm{mV}) & \mathrm{E}_{\mathrm{K}}(\mathrm{mV}) & \text { K conductance} \\&&& \text { (relative units)}\end{array}$

A) $\begin{array}{cccc} & -90 &&& -90 &&&& 1 \\\end{array}$
B) $\begin{array}{cccc} & -100 && -90 &&&& 1 \\\end{array}$
C) $\begin{array}{cccc} & -50 &&& -90 &&&& 1 \\\end{array}$
D) $\begin{array}{cccc} & 0 &&&& -90 &&&& 1 \\\end{array}$
E) $\begin{array}{cccc} & +20&&& -90 &&&& 1 \\\end{array}$
F) $\begin{array}{cccc} & -90 &&&-90 &&&& 2 \\\end{array}$