Q: Which event marks the threshold for triggering an action potential in a neuron, and what is the typical threshold voltage?

Opening of all voltage-gated Na+ channels at $$-55\ \text{mV}.$$

Question 1

During the resting state of an action potential, which channels are open and what is the primary mechanism maintaining the resting membrane potential?

Accepted Answer

Only leakage channels for Na+ and K+ are open, and the Na+/K+ ATPase pump maintains the resting membrane potential.

Question 2

Which event marks the threshold for triggering an action potential in a neuron, and what is the typical threshold voltage?

Accepted Answer

Opening of all voltage-gated Na+ channels at $$-55\ 	ext{mV}.$$

Question 3

What is the primary cause of the repolarization phase during an action potential?

Accepted Answer

Opening of voltage-gated K+ channels, allowing K+ to exit the cell.

Question 4

Which of the following best describes the 'all-or-none' phenomenon of action potentials?

Accepted Answer

Action potentials occur only if the membrane potential reaches threshold; otherwise, they do not occur at all.

Question 5

How does myelination affect the conduction velocity of action potentials in axons?

Accepted Answer

Myelination allows action potentials to jump from gap to gap, increasing conduction speed (saltatory conduction).

Question 6

A patient receives lidocaine during a dental procedure. Which step of the action potential is directly affected by this drug?

Accepted Answer

Lidocaine blocks voltage-gated Na+ channels, preventing depolarization.

Question 7

Which of the following synaptic connections is most common in the nervous system?

Accepted Answer

Axodendritic synapses

Question 8

What is the main difference between chemical and electrical synapses?

Accepted Answer

Chemical synapses use neurotransmitters and have a synaptic delay, while electrical synapses are rapid and use gap junctions.

Question 9

Which neurotransmitter is excitatory at neuromuscular junctions in skeletal muscle but inhibitory in cardiac muscle?

Accepted Answer

Acetylcholine (ACh)

Question 10

A neuron receives both excitatory and inhibitory inputs. What determines whether an action potential will be generated?

Accepted Answer

If EPSPs predominate and bring the axon hillock to threshold ($$-55\ 	ext{mV}$$), an action potential will be generated.

Question 11

Which of the following best explains why action potentials do not decay over distance?

Accepted Answer

Action potentials are regenerated at each segment of the axon by opening voltage-gated channels.

Question 12

Which phase of the action potential corresponds to the absolute refractory period, and why can't another action potential be generated during this time?

Accepted Answer

Depolarization, because voltage-gated Na+ channels are open or inactivated.

Question 13

Which equation best represents the relationship between stimulus intensity and action potential frequency?

Accepted Answer

$$	ext{Frequency} \propto 	ext{Stimulus Intensity}$$

Question 14

Which neurotransmitter is typically inhibitory and acts by opening Cl– channels, causing hyperpolarization?

Accepted Answer

GABA

Question 15

Which of the following is a direct action neurotransmitter that binds to and opens ion channels, promoting rapid responses?

Accepted Answer

Acetylcholine (ACh)

Question 16

A neuron is exposed to a neuromodulator. Which of the following effects is most likely?

Accepted Answer

The neuromodulator alters the strength of synaptic transmission by affecting neurotransmitter synthesis, release, or reuptake.

Question 17

Which clinical condition is characterized by an autoimmune attack on myelin sheaths, resulting in impaired impulse propagation?

Accepted Answer

Multiple sclerosis (MS)

Question 18

Which of the following best describes the mechanism of synaptic delay at chemical synapses?

Accepted Answer

It is caused by the time required for neurotransmitter release, diffusion, and receptor binding.

Question 19

Which of the following neurotransmitters is synthesized from the amino acid tyrosine and is involved in emotional behaviors and the biological clock?

Accepted Answer

Dopamine

Action Potentials and Synaptic Transmission: Study Notes for ANP College Students

Study Guide - Practice Questions

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