What happens at the junction between a nerve and a muscle to initiate muscle contraction?

What we know as the motor plate or motor unit is the union between the nerve or rather the nerve terminal and muscle fiber.

When the nerve fiber enters a depolarization, thus generating an action potential in its membrane, conducting electrical energy along it triggers certain "communicators" to be released at the union with the muscle (motor unit) that will indicate the muscle to contracting, these "communicators" are called neurotransmitters and an example of them is acetylcholine or Ach, when released it binds to the specific receptor for the neurotransmitter of muscle tissue, thus generating it to contract the sarcoplasmic reticulum and increase intracellular calcification levels to carry out the shortening of the muscle fiber (muscle contraction).

Explanation:

Muscle fibers are classified into three large groups according to their function and physiology, we have smooth and striated muscle and, on the other hand, specialized or cardiac muscle that has a very particular characteristic, unlike the others, which is that it is autonomous. say that it has another mechanism to be induced to contraction and that it could control muscle contraction without the presence of a nerve or nerve terminal, this is because the cardiac muscle is essential for our life to contract to generate the pumping our blood and it is very risky to depend on a nerve terminal.

On the other hand, the nerves that have a myelin sheath envelope will drive their exciting stimulation to the muscle or muscle fiber more quickly since it is the saltatory method.

The nerve terminals act at the level of the intracellular concentrations of calcium of the muscular cells as we mentioned above, that is why a muscular cell when viewed under the microscope presents a REL (superplastic smooth endoplasmic reticulum) that acts as a calcium reserve for muscle contraction. Calcium is responsible for dislodging the topoisomerase from the active site where myosin and actin bind to generate the shortening of the Z lines.