Muscle Contraction: Events at the Neuromuscular Junction

Step 1

action potential propagates down motor neuron to skeletal muscle fiber at neuromuscular junction [axon terminal + motor plate]

Step 2

Voltage gated calcium channels open and calcium ions diffuse into the terminal

Step 3

Calcium entry cause synaptic vesicles to release ACh via exocytosis

Step 4

ACh diffuse across the synaptic cleft and binds to ACh receptors which have ligand-gated cation channels

Step 5

Ligand-gated cation channels open

Step 6

Sodium ions enter the muscle fiber and potassium ions exit muscle fiber [ more sodium enter than potassium leaves —> membrane potential being less negative]

Step 7

Once membrane potential reaches threshold value an action potential propagates along the sarcolemma

Neurotransmission to Muscle fiber stopped when ACh is removed from synaptic cleft

1. Ach diffuse away from the synapse

2. Ach is broken down by enzyme Acetylcholinesterase to acetic acid and choline.