synaptic transmissions

• Chemical transmission

  • Communicate with each other within groups known as neural networks
  • Each neuron is separated from the next by an extremely tiny gap called the synapse
  • Signals within neurons are transmitted electrically, signals between neurons are transmitted chemically across the synapse.
  • when the electrical impuls reaches the end of the nuerone it triggers the release of neurotransmitters from a tiny sack called synaptic vesicles.
• Neurotransmitters

  • chemicals that diffuse across the synapse to the next neuron in the chain.

  • once it crosses the gap, it is taken up by the postsynaptic receptor sites on the dentrites of the next neuron.

  • here, the chemical message is converted back into an electrical impulse, and the process of transmission begins again in the next neuron.
• Direction of travel can only be one way


  This is because neurotransmitters are released from the presynaptic neuron terminal and received by the postsynaptic neuron.
• Types of neurotransmitters:


  • Several dozen types have been identified in the brain, spinal cord and some glands
  • Each has its own specific molecular structure that fits perfectly into a postsynaptic receptor site, similar to a lock and a key
  • Have specialist functions, e.g. acetylcholine causes muscles to contract
• Excitation and inhibition

  • Neurotransmitters have either an excitatory or inhibitory effect on the neighbouring neuron
  • Serotonin causes inhibition, making the neuron less likely to fire
  • Adrenaline causes excitation, making the neuron more likely to fire
• Summation

  1. Excitatory and inhibitory influences are summed
  2. If net effect is inhibitory, postsynaptic neuron is less likely to fire
  3. If net effect is excitatory, postsynaptic neuron is more likely to fire
  4. Action potential of postsynaptic neuron is only triggered if sum of excitatory and inhibitory signals reaches the threshold