• Striated muscle?contracts?when it receives an?impulse?from a?motor neurone?via the?neuromuscular junction
• Neuromuscular junctions work in a very similar way to synapses
• They are located?between a neurone and a muscle cell
• When an impulse travelling along the axon of a motor neurone arrives at the?presynaptic membrane, the action potential causes?calcium ions to diffuse?into the neurone
• This stimulates?vesicles?containing the neurotransmitter?acetylcholine?(ACh) to?fuse?with the presynaptic membrane
• The ACh that is released diffuses across the neuromuscular junction and?binds to receptor proteins?on the?sarcolemma?(surface membrane of the muscle fibre cell)
• This stimulates?ion channels?in the sarcolemma to?open, allowing?sodium ions?to?diffuse in
• This?depolarises the sarcolemma,?generating an?action potential?that passes down the?T-tubules?towards the centre of the muscle fibre
• These action potentials cause?voltage-gated calcium ion channel proteins?in the membranes of the?sarcoplasmic reticulum?(which lie very close to the T-tubules) to?open
• Calcium ions?diffuse?out of the sarcoplasmic reticulum?(SR) and?into the sarcoplasm?surrounding the myofibrils
• Calcium ions?bind to troponin molecules, stimulating them to?change shape
• This causes the?troponin?and?tropomyosin?proteins to?change position?on the thin (actin) filaments
• The?myosin-binding sites are exposed?to the actin molecules
• The process of muscle contraction (known as the sliding filament model) can now begin
• There are multiple neuromuscular junctions spread across several muscle fibres within the muscle

The structure of the neuromuscular junction

The steps involved in muscle contraction via the neuromuscular junction

Comparison of Cholinergic Synapses and Neuromuscular Junctions