Question

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 nerve signals trigger muscle action.

Step 1: Understand the sequence of events

To find the event that directly occurs due to an action potential reaching the end of a motor neuron, we need to look at the chronological steps of synaptic transmission at the neuromuscular junction:

1. An action potential travels down the motor neuron to the axon terminal.
2. The depolarization opens voltage-gated calcium channels, allowing calcium to enter the neuron.
3. This influx of calcium triggers synaptic vesicles to fuse with the membrane and release acetylcholine (ACh) into the synaptic cleft.
4. ACh diffuses across the cleft and binds to ACh receptors on the muscle fiber's sarcolemma.
5. This binding opens ligand-gated ion channels, allowing \( \text{Na}^+ \) to rush into the muscle cell, depolarizing it.
6. This depolarization triggers an action potential along the sarcolemma of the muscle fiber.
7. Eventually, acetylcholinesterase (AChE) breaks down ACh to end the signal.

Step 2: Identify the direct consequence

The question asks for the event that directly occurs due to the action potential generated on the motor neuron.

• The arrival of the action potential at the motor neuron terminal is the signal that triggers the exocytosis (release) of the neurotransmitter, acetylcholine (ACh), into the synaptic cleft.
• Therefore, ACh is released at the synapse is the immediate, direct consequence of the motor neuron's action potential.
• Other events like ACh binding to receptors, \( \text{Na}^+ \) influx, and the muscle action potential occur downstream as a result of this initial release.

Answer:

ACh is released at the synapse.