Question

Diagram the events that occur at the neuromuscular junction. Be sure to include the somatic motor neuron, axon terminal, synaptic cleft, synaptic vesicles, motor end plate, and appropriate neurotransmitter(s), ion channel(s), and membrane receptor(s).

Answer 1

At the neuromuscular junction, an action potential from a motor neuron triggers the release of acetylcholine, which then binds to receptors on the muscle fiber, initiating muscle contraction. Acetylcholinesterase breaks down acetylcholine to terminate the signal.

Step-by-step explanation:

Neuromuscular Junction Diagram

The neuromuscular junction is a specialized synapse between a somatic motor neuron and a muscle fiber. The sequence of events is as follows:

1. An action potential travels down the somatic motor neuron's axon reaching the axon terminal.
2. The arrival of the action potential triggers the opening of voltage-gated calcium channels in the axon terminal, leading to an influx of calcium ions.
3. Calcium ions stimulate the release of the neurotransmitter acetylcholine (ACh) from synaptic vesicles into the synaptic cleft.
4. ACh diffuses across the synaptic cleft and binds to nicotinic acetylcholine receptors on the motor end plate, a part of the muscle fiber's sarcolemma.
5. Binding of ACh to its receptors opens ligand-gated sodium channels, allowing an influx of sodium ions, leading to depolarization of the sarcolemma.
6. This depolarization spreads across the sarcolemma and down the muscle fiber's T-tubules, initiating a muscle contraction.
7. Finally, acetylcholinesterase breaks down ACh in the synaptic cleft, terminating the signal and allowing the muscle fiber to relax if no more nerve impulses arrive.

At the neuromuscular junction, the precision of communication ensures that each nerve impulse results in a muscle fiber contraction. The strength and number of contracting fibers are influenced by the frequency at which the motor neuron fires.