Answer:
1. An action potential is propagated down the lower motor neuron.
4. Vesicles containing glutamate fuse with the nerve terminal.
3. Acetylcholine binds its receptor and causes depolarization.
2. Calcium levels increase in the cytoplasm of the muscle cell.
5. Contraction
Explanation:
In the activation for the somatic motor neuron pathway;
first, an action potential is propagated down the lower motor neuron; this results to vesicles containing glutamate to fuse with the nerve terminal and then results to opening of the acetylcholine receptor channel. The opening leads to increase in Na+ and K+ ions permeabiity which causes depolarization. This depolarization then results to the generation of an action potential in the muscle membrane. As the membrane depolarization approaches a specialized region, it increase the calcium level in the cytoplasm of the muscle cell, as calcium moves from the intracellular store into the cytoplasm. This rise in cytoplasmic calcium then induces muscle contraction.
The correct sequence of activation for the somatic motor neuron pathway -
When an action potential reaches the axon terminal, calcium enters the axon terminal. The synaptic vesicles fuse with the nerve terminal. This causes exocytosis of acetylcholine into the synaptic cleft. Acetylcholine binds to its receptors.
The binding of Ach to receptors results in depolarizing muscle cell membrane. The action potential is carried down by T tubules to stimulate the sarcoplasmic reticulum. It releases calcium in the cytoplasm of the muscle cell. This facilitates cross-bridge formation and contraction of skeletal muscle occurs.
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