Synapses

• Synapse: a junction between two neurones, consisting of a gap across which impulses pass by diffusion of a neurotransmitter
• Synaptic cleft: small gap between each pair of neurones
• Inside the neurones axon, there are 100s of tiny vacuoles (vessicles each contain a chemical called a neurotransmitter)
• When an impulse arrives at the synapse, the vessicles move to the cell membrane and empty their content into the synaptic cleft
• The neurotransmitter quickly diffuses across the tiny gap and attaches to receptor molecules in the cell membrane of the relay neurone

  
  

  This can happen because the shape of the neurotransmitter molecules is complimentary to the shape of the receptor molecule
• Many drugs e.g. heroin act upon synapses