 The nerve impulse is characterised by a great influx of sodium ions through channels in the neuron 's cell membrane followed by an efflux of potassium ions through other channels . The neuron is unable to fire again for a short time ( known as the refractory period ) , which is mediated by another potassium channel . The flow through these ion channels is governed by a " gate " which is opened by either a voltage change or a chemical messenger known as a ligand ( such as a neurotransmitter ) . These channels are another target for anticonvulsant drugs . 
