Synapse: Properties of Nerve Fibres

A synapse is the junction between two nerve cells, separated by a minute gap (the synaptic cleft), across which a neurotransmitter bridges the impulse from one neuron to the next.

1. Properties of nerve fibres : Nerve fibres crossing such junctions display a defined set of physiological properties. Excitability (irritability) is the ability of a polarised nerve membrane to sense a stimulus and enter an active state; conductivity is the ability to transmit that excitation onward. A stimulus is any detectable physical, chemical or electrical change able to trigger excitation, but it must reach a minimum intensity -- the threshold (liminal) stimulus -- to be effective at all: a weaker, subliminal stimulus produces no response, while a stronger, supraliminal stimulus produces exactly the same size of impulse as a threshold one (this is the summation effect in reverse: several rapid, individually sub-threshold stimuli can still add up to trigger an impulse). …