Outline the structures and processes involved in synaptic transmission (6 marks)

Unlike within a neuron where signals are transmitted electrically , between two different neuron's signals are transmitted chemically, as the impulse travels across a synapse. Synaptic transmission involves the movement of an impulse from the presynaptic terminal, across the synaptic cleft and to the post synaptic receptor sites. The process begins when an impulse (action potential) reaches the presynaptic terminal located at the end of a neuron. Small sacs called vesicles, which are located on the presynaptic terminal, contain neurotransmitters and are stimulated to release these when the impulse arrives. As a result the chemical messengers pass across the synaptic cleft and bind to post synaptic receptor sites, to cause a specific response, which will either be excitatory or inhibitory. At this stage of the process it is also important to note that the chemical signal is converted back to electrical, as the impulse continues its journey along the next neuron.