$$3\mathrm{Na}^+ \text{ out}, 2\mathrm{K}^+ \text{ in}$$

Question 1

Which of the following best describes the resting membrane potential of a typical neuron?

Accepted Answer

The inside of the cell is more negative than the outside, typically -70 mV to -85 mV.

Question 2

What is the main contributor to the negative charge inside the plasma membrane of a neuron?

Accepted Answer

Negatively charged proteins that cannot cross the membrane

Question 3

Which equation correctly represents the action of the Na⁺/K⁺ pump in maintaining membrane potential?

Accepted Answer

$$3\mathrm{Na}^+ 	ext{ out}, 2\mathrm{K}^+ 	ext{ in}$$

Question 4

During an action potential, what causes the cell to become depolarized?

Accepted Answer

Voltage-gated Na⁺ channels open and Na⁺ rushes in

Question 5

Which of the following best explains why plasma membranes are described as 'selectively permeable'?

Accepted Answer

They allow certain ions and molecules to pass while restricting others.

Question 6

A patient is experiencing muscle weakness due to a genetic defect in voltage-gated Na⁺ channels. Which process is most directly affected?

Accepted Answer

Depolarization during action potential

Question 7

Which of the following events occurs FIRST during excitation-contraction coupling in skeletal muscle?

Accepted Answer

Action potential travels down T tubule

Question 8

What is the role of acetylcholine (ACh) at the neuromuscular junction?

Accepted Answer

It binds to receptors on the motor end plate, increasing Na⁺ permeability.

Question 9

Which of the following best describes the refractory period in neurons?

Accepted Answer

The time during which the membrane cannot respond to another stimulus

Question 10

During cross-bridge cycling in muscle contraction, what is the immediate consequence of ATP binding to the myosin head?

Accepted Answer

Myosin head detaches from actin

Question 11

Which of the following is TRUE regarding the direction of action potential propagation in neurons and skeletal muscle cells?

Accepted Answer

It is unidirectional, permitting rapid communication between parts of a cell.

Question 12

If the permeability of the plasma membrane to K⁺ suddenly increases, what is the most likely effect on the membrane potential?

Accepted Answer

The membrane potential will become more negative (hyperpolarization).

Question 13

Which of the following steps occurs LAST during muscle fiber contraction?

Accepted Answer

The muscle fiber shortens as contraction occurs

Question 14

A toxin blocks the release of acetylcholine at the neuromuscular junction. What is the most immediate effect?

Accepted Answer

Action potential cannot be generated in the sarcolemma

Question 15

Which formula best represents the change in membrane potential ($$\Delta V) $$when Na⁺ ions rush into the cell?

Accepted Answer

$$\Delta V = V_{	ext{inside}} - V_{	ext{outside}}$$

Question 16

Which of the following is the correct sequence of events in excitation-contraction coupling?

Accepted Answer

ACh binding → Action potential → Ca²⁺ release → Myosin-actin cross-bridge

Question 17

Which of the following best explains why K⁺ moves more easily through its channel than Na⁺?

Accepted Answer

K⁺ channels are more numerous and have a higher permeability than Na⁺ channels.

Question 18

A patient with a mutation in troponin cannot bind calcium. What is the most direct consequence for muscle contraction?

Accepted Answer

Active sites on actin remain covered, preventing cross-bridge formation.

Question 19

Which of the following is a direct result of the action potential reaching the axon terminal of a motor neuron?

Accepted Answer

Release of acetylcholine into the synaptic cleft

Membrane Potentials and Excitation-Contraction Coupling in Muscle Physiology

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