Describe what an action potential is and how is it transmitted. Refer to the action of stimuli and neurons in your answer.

An action potential is when a neuron sends an electrical signal down an axon, away from the cell body (soma). A stimulus is detected by a motor neuron e.g. through mechanoreceptors that detect touch on the skin. This causes voltage gated ion channels to open and there is an influx of sodium ions into the neuron, which diffuse down a concentration gradient. This causes depolarisation of the neuron membrane. When depolarisation exceeds the threshold potential it activates voltage-gates sodium channels, causing an action potential. Ion movement occurs only at the Nodes of Ranvier. As the action potential is transmitted across the axon, the ion channels at the next node open, causing transmission across the neuron. This is called saltatory conduction.