Question

spotlight figure 10.10: neuromuscular junction (nmj)
4 parts | 0.25 of 1 point

events at nmj

which of the following events directly occurs due to an action potential generated on the motor neuron?

choose the best answer.

ach binds to ach receptors.
ache breaks down ach in the synaptic cleft.
\\(\text{na}^+\\) rushes into the sarcolemma.
an action potential is generated on the muscle fiber.
ach is released at the synapse.

Explanation:

🆕 New Concept Discovered: Neuromuscular Junction Signaling
How electrical signals in nerves trigger chemical signals to muscles.

Step 1: Understand the initial trigger

The question asks for the event that directly occurs due to an action potential (an electrical impulse) arriving at the end of the motor neuron.

When an action potential travels down the motor neuron and reaches the axon terminal, it depolarizes the terminal membrane. This electrical change opens voltage-gated calcium channels, allowing calcium ions to enter the neuron.

Step 2: Identify the immediate consequence

The influx of calcium ions triggers synaptic vesicles inside the motor neuron terminal to fuse with the outer membrane. This fusion releases the neurotransmitter acetylcholine (ACh) into the synaptic cleft via exocytosis.

Therefore, the direct result of the action potential reaching the end of the motor neuron is the release of ACh into the synaptic cleft.

Step 3: Evaluate the other options

• ACh binds to ACh receptors: This happens after ACh is released and diffuses across the synaptic cleft.
• AChE breaks down ACh in the synaptic cleft: This is a cleanup step that occurs later to stop the signal.
• \( \text{Na}^+ \) rushes into the sarcolemma: This occurs only after ACh binds to its receptors on the muscle cell, opening chemically gated ion channels.
• An action potential is generated on the muscle fiber: This is the final step of the transmission process, occurring after \( \text{Na}^+ \) entry depolarizes the muscle membrane.

Answer:

ACh is released at the synapse.