synaptic transmission

• signals within neurones are transmitted electrically but signals between neurones are transmitted chemically across synapses. When the electrical impulse reaches the end of the neurone it triggers the release of neurotransmitter from vesicles and once a neurotransmitter crosses the synapse it is taken up by a postsynaptic receptor site on the next neurone
• neurotransmitters are chemical that diffuse across the synapse to the next neurone. Each neurotransmitter has its own specific molecular structure that fits perfectly into a postsynaptic receptor site and each neurotransmitter has specific functions like ACH causes muscles to contract and serotonin affects mood and social behaviour
• excitatory neurones increase the positive charge f the postsynaptic neurone which makes it more likely that the postsynaptic neurone will fire. Inhibitory neurones increase the negative charge of the postsynaptic neurone which makes it less likely that the postsynaptic neurone will fire. Adrenaline is usually excitatory and serotonin is usually inhibitory
• neurones can only travel in one direction at a synapse because:

  • vesicles containing neurotransmitter are only in the presynaptic neurone
  • there are no receptors on the presynaptic neurone
  • diffusion of neurotransmitter across synapse is from high concentration to low concentration