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.