Question 1

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

Accepted Answer

[V B 5]. Binding of acetylcholine (ACh) to receptors in the muscle end plate opens channels that allow passage of both $\mathrm{Na}^{+}$and $\mathrm{K}^{+}$ions. $\mathrm{Na}^{+}$ions will flow into the cell down its electrochemical gradient, and $\mathrm{K}^{+}$ions will flow out of the cell down its electrochemical gradient. The resulting membrane potential will be depolarized to a value that is approximately halfway between their respective equilibrium potentials.

Question 2

An inhibitory postsynaptic potential

Accepted Answer

[ $\mathrm{VC} 2 \mathrm{~b}$ ]. An inhibitory postsynaptic potential hyperpolarizes the postsynaptic membrane, taking it farther from threshold. Opening $\mathrm{Cl}^{-}$channels would hyperpolarize the postsynaptic membrane by driving the membrane potential toward the $\mathrm{Cl}^{-}$equilibrium potential (about $-90 \mathrm{mV}$ ). Opening $\mathrm{Ca}^{2+}$ channels would depolarize the postsynaptic membrane by driving it toward the $\mathrm{Ca}^{2+}$ equilibrium potential.

Question 3

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

Accepted Answer

[II D 2 a]. Inhibition of $\mathrm{Na}^{+}, \mathrm{K}^{+}$-adenosine triphosphatase (ATPase) leads to an increase in intracellular $\mathrm{Na}^{+}$concentration. Increased intracellular $\mathrm{Na}^{+}$ concentration decreases the $\mathrm{Na}^{+}$gradient across the cell membrane, thereby inhibiting $\mathrm{Na}^{+}-\mathrm{Ca}^{2+}$ exchange and causing an increase in intracellular $\mathrm{Ca}^{2+}$ concentration. Increased intracellular $\mathrm{Na}^{+}$concentration also inhibits $\mathrm{Na}^{+}$-glucose cotransport.

Question 4

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

Accepted Answer

[VI B 1-4]. The correct sequence is action potential in the muscle membrane; depolarization of the $\mathrm{T}$ tubules; release of $\mathrm{Ca}^{2+}$ from the sarcoplasmic reticulum (SR); binding of $\mathrm{Ca}^{2+}$ to troponin $\mathrm{C}$; cross-bridge formation; and splitting of adenosine triphosphate (ATP).

Question 5

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?

Accepted Answer

[II D 2 a, E 1]. In the "usual" $\mathrm{Na}^{+}$gradient, the $\left[\mathrm{Na}^{+}\right]$is higher in extracellular than in intracellular fluid (maintained by the $\mathrm{Na}^{+}-\mathrm{K}^{+}$pump). Two forms of transport are energized by this $\mathrm{Na}^{+}$gradient-cotransport and countertransport. Because glucose is moving in the same direction as $\mathrm{Na}^{+}$, one can conclude that it is cotransport.

Question 6

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

Accepted Answer

[VI A 3]. In the mechanism of excitation-contraction coupling, excitation always precedes contraction. Excitation refers to the electrical activation of the muscle cell, which begins with an action potential (depolarization) in the sarcolemmal membrane that spreads to the T tubules. Depolarization of the T tubules then leads to the release of $\mathrm{Ca}^{2+}$ from the nearby sarcoplasmic reticulum (SR), followed by an increase in intracellular $\mathrm{Ca}^{2+}$ concentration, binding of $\mathrm{Ca}^{2+}$ to troponin $\mathrm{C}$, and then contraction.

Question 7

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

Accepted Answer

[II D 2]. All of the processes listed are examples of primary active transport (and therefore use adenosine triphosphate [ATP] directly), except for absorption of glucose by intestinal epithelial cells, which occurs by secondary active transport (i.e., cotransport). Secondary active transport uses the $\mathrm{Na}^{+}$gradient as an energy source and, therefore, uses ATP indirectly (to maintain the $\mathrm{Na}^{+}$gradient).

Question 8

Which of the following causes rigor in skeletal muscle?

Accepted Answer

$[\mathrm{VI} B]$. Rigor is a state of permanent contraction that occurs in skeletal muscle when adenosine triphosphate (ATP) levels are depleted. With no ATP bound, myosin remains attached to actin and the cross-bridge cycle cannot continue. If there were no action potentials in motoneurons, the muscle fibers they innervate would not contract at all, since action potentials are required for release of $\mathrm{Ca}^{2+}$ from the sarcoplasmic reticulum (SR). When intracellular $\mathrm{Ca}^{2+}$ concentration increases, $\mathrm{Ca}^{2+}$ binds troponin $\mathrm{C}$, permitting the cross-bridge cycle to occur. Decreases in intracellular $\mathrm{Ca}^{2+}$ concentration cause relaxation.

Question 9

Degeneration of dopaminergic neurons has been implicated in

Accepted Answer

[ $\mathrm{C} 4 \mathrm{~b}$ (3)]. Dopaminergic neurons and $\mathrm{D}_{2}$ receptors are deficient in people with Parkinson disease. Schizophrenia involves increased levels of $\mathrm{D}_{2}$ receptors. Myasthenia gravis and curare poisoning involve the neuromuscular junction, which uses acetylcholine (ACh) as a neurotransmitter.

Question 10

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

Accepted Answer

[III A]. Osmolarity is the concentration of particles (osmolarity $=\mathrm{g} \times \mathrm{C}$ ). When two solutions are compared, that with the higher osmolarity is hyperosmotic. The $1 \mathrm{mM} \mathrm{CaCl}_{2}$ solution (osmolarity $=3 \mathrm{mOsm} / \mathrm{L}$ ) is hyperosmotic to $1 \mathrm{mM} \mathrm{NaCl}$ (osmolarity $=2 \mathrm{mOsm} / \mathrm{L}$ ). The $1 \mathrm{mM}$ glucose, $1.5 \mathrm{mM}$ glucose, and $1 \mathrm{mM}$ sucrose solutions are hyposmotic to $1 \mathrm{mM} \mathrm{NaCl}$, whereas $1 \mathrm{mM} \mathrm{KCl}$ is isosmotic.

Question 11

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?

Accepted Answer

[II D c]. $\mathrm{H}^{+}$secretion by gastric parietal cells occurs by $\mathrm{H}^{+}-\mathrm{K}^{+}$adenosine triphosphatase (ATPase), a primary active transporter.

Question 12

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

Accepted Answer

[IV E 2]. Elevated serum $\mathrm{K}^{+}$concentration causes depolarization of the $\mathrm{K}^{+}$ equilibrium potential and therefore depolarization of the resting membrane potential in skeletal muscle. Sustained depolarization closes the inactivation gates on $\mathrm{Na}^{+}$channels and prevents the occurrence of action potentials in the muscle.

Question 13

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

Accepted Answer

[VII B]. The steps that produce contraction in smooth muscle occur in the following order: various mechanisms that raise intracellular $\mathrm{Ca}^{2+}$ concentration, including depolarization of the sarcolemmal membrane, which opens voltage-gated $\mathrm{Ca}^{2+}$ channels, and opening of ligand-gated $\mathrm{Ca}^{2+}$ channels; $\mathrm{Ca}^{2+}$-induced $\mathrm{Ca}^{2+}$ released from SR; increased intracellular $\mathrm{Ca}^{2+}$ concentration; binding of $\mathrm{Ca}^{2+}$ to calmodulin; increased myosin-lightchain kinase; phosphorylation of myosin; binding of myosin to actin; cross-bridge cycling, which produces contraction

Question 14

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)$\begin{array}{cccc} & -90 &&&-90 &&&& 2 \
\end{array}$

Accepted Answer

[IV C]. Data sets A and F have no difference between membrane potential
(E
m
) and E
K and thus have no driving force or current flow; although data set F has the
higher K+ conductance, this is irrelevant since the driving force is zero. Data sets C, D, and
E all will have outward K+ current, since E
m is less negative than EK; of these, data set E will
have the largest outward K+ current because it has the highest driving force. Data set B will
have inward K+ current since E
m is more negative than EK.

Quiz 1: Cell Physiology

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

An inhibitory postsynaptic potential

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

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

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?

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

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

Which of the following causes rigor in skeletal muscle?

Degeneration of dopaminergic neurons has been implicated in

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

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 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

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

Quiz 1: Cell Physiology

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

An inhibitory postsynaptic potential

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

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

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 Na+\mathrm{Na}^{+}Na+ gradient across the cell membrane?

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

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

Which of the following causes rigor in skeletal muscle?

Degeneration of dopaminergic neurons has been implicated in

Assuming complete dissociation of all solutes, which of the following solutions would be hyperosmotic to 1mMNaCl1 \mathrm{mM} \mathrm{NaCl}1mMNaCl ?

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

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

In contraction of gastrointestinal smooth muscle, which of the following events occurs after binding of Ca2+\mathrm{Ca}^{2+}Ca2+ to calmodulin?

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

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?

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

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 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

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