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.
- Nerve impulse at terminal branches of axon→ Increases Ca2+ permeability → Ca2+ influx.
- Results in exocytosis of neurotransmitter “acetylcholine” from presynaptic vesicles into synaptic cleft.
- Acetylcholine binds with specific receptors (Nm) on motor-end-plate.
- Activates ligand-gated Na+ channels→ Na+ influx → Generates depolarized end-plate potential.
- Membrane activated above threshold (firing) level → Action potential develops→ Muscle contraction occurs.
Exam Important
- Skeletal muscle fibers are innervated by large myelinated (Aα) motor neurons.
- Motor neuron together with all innervating muscle fibers – ‘Motor unit’.
- Junction between motor neuron branch & muscle fiber – Neuromuscular junction/myoneural junction.
- Acetylcholine binds to receptors on the postsynaptic sarcolemmal membrane.
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