Synaptic transmission

• What is a synapse?

  •Neurons communicate with each other within groups called neural networks

  •Each neuron separated from the next by a synapse
• What is synaptic transmission?

  •The process by which one neuron communicates with another

  •A nerve impulse passes across the synaptic gap from a pre-synaptic neuron to a post-synaptic neuron

  •Signals within neurons are transmitted electrically

  •Signals between neurons are transmitted chemically by synaptic transmission
• Synaptic transmission - chemical

  •When the electrical impulse reaches the end of the neuron (presynaptic terminal) it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles

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

  •Once the neurotransmitter crosses the gap, it is taken up by the postsynaptic receptor sites (dendrites of next neuron)

  •The chemical message is converted back into an impulse and process of transmission begins again with another neuron
• Steps of synaptic transmission

  1.Information is passed down the axon of the neuron as an electrical impulse known as

  action potential. Once the action potential reaches the end of the axon it needs to be transferred to another neuron or tissue.

  2. It must cross over the synaptic gap (synaptic cleft) between the pre-synaptic neuron and post-synaptic neuron.

  3. At the end of the neuron (in the axon terminal) are the synaptic vesicles, which contain chemical messengers, known as neurotransmitters.
• Steps of synaptic transmission

  4.When the electrical impulse reaches these synaptic vesicles, it triggers the vesicles to release neurotransmitters into the synaptic cleft.

  5.Neurotransmitters then carry the signal across the synaptic cleft. They bind to receptor sites on the post-synaptic cell

  6.The neurotransmitter makes it either more likely or less likely that the post-synaptic neuron will ‘fire’.

  7.Any remaining neurotransmitter that isn’t absorbed by post synaptic receptors is reabsorbed and recycled back
• Excitation and inhibition

  • Neurotransmitters have either an excitatory or inhibitory effect on the neighboring neuron
  • excitatory: increases positive charge and making it more likely to fire (e.g., adrenaline)
  • inhibitory: increases negative charge and makes it less likely to pass on the electrical impulse (e.g., serotonin)
• what is summation?


  The likelihood of the cell firing is determined by adding up the excitatory and inhibitory synaptic input
• Spatial summation

  Large number of EPSP (excitatory post synaptic potential) are generated at different synapses on the same post synaptic neuron at the same time.
• Temporal summation

  Large number of EPSP are generated at the same synapse by a series of high frequency action potentials on the pre synaptic neuron.