NEUROMUSCULAR JUNCTION AND EVENTS

NEUROMUSCULAR JUNCTION AND EVENTS

• Skeletal muscle fibers are innervated by large myelinated (Aα) motor neurons.
• Each neuron divides into collateral & supplies muscle fibers.
• Motor neuron together with all innervating muscle fibers – ‘Motor unit’.
• Junction between motor neuron branch & muscle fiber – Neuromuscular junction/myoneural junction.
  • Typically a synaptic junction between neuron & muscle fiber.

Neuromuscular sequence of events:

• Events are similar to neuronic synaptic processes.

1. Nerve impulse at terminal branches of axon → Increases Ca2+ permeability → Ca2+ influx.

2. Results in exocytosis of neurotransmitter “acetylcholine” from presynaptic vesicles into synaptic cleft.

3. Acetylcholine binds with specific receptors (Nm) on motor-end-plate.

4. Activates ligand-gated Na+ channels → Na+ influx → Generates depolarized end-plate potential.

5. Membrane activated above threshold (firing) level → Action potential develops → Muscle contraction occurs.

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