Q: Which equation best represents the movement of ions by the Na\textsuperscript{+}/K\textsuperscript{+} ATPase during one cycle?

$3\ \mathrm{Na}^+_{\text{in}} + 2\ \mathrm{K}^+_{\text{out}} + \mathrm{ATP} \rightarrow 3\ \mathrm{Na}^+_{\text{out}} + 2\ \mathrm{K}^+_{\text{in}} + \mathrm{ADP} + \mathrm{P}_i$

Question 1

Which of the following best describes the function of the sodium-potassium ion pump (Na	extsuperscript{+}/K	extsuperscript{+} ATPase) in maintaining the resting membrane potential of a muscle cell?

Accepted Answer

It moves three sodium ions out of the cell and two potassium ions into the cell, using ATP to maintain higher sodium concentration in the ECF and higher potassium concentration in the cytosol.

Question 2

A muscle fiber is at rest. Which of the following statements about the distribution of ions and charges across its plasma membrane is correct?

Accepted Answer

There is a thin layer of negative ions in the cytosol and a thin layer of positive ions in the extracellular fluid, creating a polarized membrane.

Question 3

Which type of ion channel is always open and allows ions to move according to their gradients, contributing to the resting membrane potential?

Accepted Answer

Leak channels

Question 4

If the sodium-potassium pump in a muscle cell stopped functioning due to lack of ATP, what would be the immediate effect on ion gradients?

Accepted Answer

The gradients of sodium and potassium ions would dissipate, leading to a loss of resting membrane potential.

Question 5

Which equation best represents the movement of ions by the Na	extsuperscript{+}/K	extsuperscript{+} ATPase during one cycle?

Accepted Answer

$3\ \mathrm{Na}^+_{	ext{in}} + 2\ \mathrm{K}^+_{	ext{out}} + \mathrm{ATP} ightarrow 3\ \mathrm{Na}^+_{	ext{out}} + 2\ \mathrm{K}^+_{	ext{in}} + \mathrm{ADP} + \mathrm{P}_i$

Question 6

A patient is given a drug that blocks all voltage-gated sodium channels in their muscle fibers. What is the most likely effect on muscle function?

Accepted Answer

The muscle fibers will be unable to generate action potentials, resulting in paralysis.

Question 7

Which of the following best explains why the resting membrane potential is negative inside the cell, even though positive ions are involved?

Accepted Answer

Potassium ions diffuse out of the cell more easily than sodium ions enter, resulting in a net loss of positive charge from the cytosol.

Question 8

If the concentration gradient for potassium ions ($[K^+]$) across the muscle cell membrane is increased, what will happen to the resting membrane potential?

Accepted Answer

The resting membrane potential will become more negative, as more potassium will leave the cell.

Question 9

Which of the following statements about electrical gradients and concentration gradients is correct in the context of potassium ion movement in a resting muscle fiber?

Accepted Answer

The concentration gradient favors potassium movement into the ECF, while the electrical gradient favors movement into the cytosol.

Question 10

A muscle cell is exposed to a toxin that permanently opens all ligand-gated sodium channels. What is the most likely immediate effect on the membrane potential?

Accepted Answer

The membrane potential will depolarize as sodium ions rush into the cell.

Question 11

Which of the following best defines 'voltage' as it applies to muscle cell membranes?

Accepted Answer

The difference in electrical potential between two points, measured in millivolts (mV).

Question 12

During the resting state of a muscle fiber, which of the following is true regarding the movement of sodium and potassium ions?

Accepted Answer

Potassium ions diffuse out of the cell more easily than sodium ions enter.

Question 13

Which of the following scenarios would most likely result in a loss of the negative resting membrane potential in a muscle cell?

Accepted Answer

Inhibition of the Na	extsuperscript{+}/K	extsuperscript{+} ATPase, leading to equalization of sodium and potassium concentrations across the membrane.

Question 14

Which of the following best describes the concept of an 'electrical gradient' in the context of muscle cell membranes?

Accepted Answer

A separation of charges with equal numbers of positive and negative ions separated by a barrier.

Question 15

A researcher measures the membrane potential of a muscle cell and finds it to be $-90\ \mathrm{mV}$. What does this value represent?

Accepted Answer

The inside of the cell is more negative than the outside by 90 millivolts.

Membrane Potential in Muscle Cells: Foundations of Electrophysiology - 10.3-10.4

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