Neurotransmitters

Neurons connect with other neurons or muscle fibres at a synaptic cleft Neurotransmitters relay impulses across the synaptic cleft

Neurotransmitters are stored in vesicles in the axon ending of the presynaptic neurone Arrival of an impulse causes vesicles to fuse with the presynaptic neurons membrane and release neurotransmitters into the synaptic cleft

Neurotransmitters diffuse across the cleft and then bind to receptors on the postsynaptic membrane Receptors determine whether the signal is excitatory or inhibitory

A minimum number of neurotransmitter molecules attach to receptors in order to reach the threshold on the post synaptic membrane to transmit the impulses

A series of weak stimuli can release enough neurotransmitter to trigger an impulse Convergent neural pathways can relajase enough neurotransmitter molecules to reach threshold and trigger an impulse

Neurotransmitters must be removed from the synaptic cleft to prevent continuous stimulation of post synaptic neurons Neurotransmitters are removed by enzymes (acetylcholine) or reuptake (noradrenaline)