How does an action potential cause contraction in skeletal muscle?

The point at which a motor neurone synapses with a muscle fibre is called the neuromuscular junction. The unmyelinated nerve fibre stops around 30 nanometers before the muscle fibre, leaving a gap called the synaptic cleft, with the nerve ending being referred to as the pre synaptic membrane, and the muscle fibre end called the post synaptic membrane.

When an action potential reaches the nerve ending, the sudden depolarisation causes an influx of calcium ions through voltage gated channels. These ions bind to specific receptors on vesicles within the motor neuron, causing them to move towards and fuse with the presynaptic membrane and release neurotransmitter into the synaptic cleft. The neurotransmitter diffuses across the cleft and binds to its specific receptors on te post synaptic membrane. The binding of the neurotransmitter causes the opening of ligand gated ion channels. The influx of negatively charged ions causes depolarisation of the muscle fibre, setting off the mechanisms that lead to muscle contraction.