Neuromuscular Junction And Its Mechanism

Synapse between a somatic motor neuron and skeletal muscle fiber, called neuromuscular junction (NMJ).

Axon of motor neuron is divided in many branches, each branch of axon end attach to the muscle membrane (sarcolemma). This region of sarcolemma where axon terminal is embedded, known as the motor end plate. 

Each branch of a somatic motor neuron form a junction with the skeletal muscle fiber.

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• Axon Terminal Axon part of nerve fibers divided into several branches, end of a single axon branch, known as axon terminal.

• Motor End Plate A single branch of axon terminal is embedded at muscle membrane. Bulb like expansion of axon terminal is occurs at sarcolemma. 

• Presynaptic Membrane Membrane of nerve ending.

• Postsynaptic Membrane Membrane of muscle fiber.

• Synaptic Cleft Space between postsynaptic and presynaptic membrane.

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Transfer of information from motor nerve ending to muscle fiber through NMJ to initiate muscle contraction. A nerve fiber arise from spinal cord that end attach to a muscle fiber. That point where nerve fiber attach to the muscle fiber, make a junction called NMJ (Gap between the end of neuron and muscle fibers or Junction or synapse between terminal branch of nerve fibers and muscle fiber, called neuromuscular junction).

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Neuromuscular Transmission

Chemical secreted from neuromuscular junction, called neuromuscular transmission. The chemical is secreted in three following steps   

• Release of acetylcholine
• Activation of acetylcholine receptors
• Production of muscle action potential

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Physiology of Neuromuscular transmission

A nerve action potential (nerve impulse) elicits muscle action potential in the following way :

• Release of acetylcholine  Action potential comes to nerve terminal, that potential open the voltage gated calcium channels at nerve terminal. The movement of calcium ion inside the cell. Vesicles filled with acetylcholine present at nerve terminal. Calcium ions evoked vesicle of Ach. Acetylcholine or Ach vesicles are ruptured and release acetylcholine or Ach.

• Activation of Ach receptors Two molecules of  Acetylcholine or Ach binding  to acetylcholine receptor on the motor end plate. Voltage gated sodium channels are open and influx of sodium ion in muscle fibers.

• Production of muscle action potential Numbers of sodium ion inside muscle fiber are increase and generate action potential that potential cause muscle contraction.

Physiology of Neuromuscular Transmission 

Importance of Neuromuscular Transmission  

1. Secrete acetylcholine transmitter, which involve in many physiology of body.
2. Regulate nerve impulse.
3. Help to produce muscle contraction.
4. Neuromuscular transmission completely control cells potential including depolarization, re-polarization and maintain resting potential on cell membrane.