The structure of a synapse

• Synapses transmit information via neurotransmitters.
• Neurones are separated by the synaptic cleft.
• The neurone that releases the neurotransmitter across the synaptic cleft is known as the presynaptic neurone. The axon of this neurone ends in the synaptic knob.
• The synaptic knob of a presynaptic neurone possesses many mitochondria and large amounts of endoplasmic reticulum. These are required to manufacture the neurotransmitters in the axon.
• Neurotransmitters are stored in synaptic vesicles in the presynaptic neurone. Once the neurotransmitter is released from the vesicles it diffuses across to the postsynaptic neurone, which possesses specific receptor proteins on its membrane to receive it.
• Synapses have two main roles. (1) They allow a single impulse along one neurone to initiate new impulses in multiple neurones at a synapse. (2) They allow a number of impulses to be combined at one synapse.