Synaptic Transmission

• Synaptic Transmission - The process by which a nerve impulse passes across the synaptic gap from one neuron (pre synaptic neuron) to another neuron (post synaptic neuron)
• Synaptic Transmission Process (1): Information is passed down the axon as an electrical impulse known as action potential
• Synaptic Transmission Process (2): Once the action potential reaches the end of the axon it needs to be transferred to another neuron, by crossing the synaptic gap
• Synaptic Transmission Process (3): at the end of the neuron (in the axon terminal) are synaptic vesicles which contains neurotransmitters
• Synaptic Transmission Process (4): The electrical impulse (action potential) stimulates the release of transmitters from the synaptic vesicles
• Synaptic Transmission Process (5): Neurotransmitters then carry the signal across the synaptic gap binding to receptor sites on the postsynaptic cell activating them
• Synaptic Transmission Process (6): Once the receptors or postsynaptic cells have been activated, they produce excitatory or inhibitory effects on the postsynaptic cell
• Synaptic Transmission Process (7): Inhibitory neurotransmitters (GABA) make them less likely to fire, whereas excitatory neurotransmitters (noradrenaline) making them more likely to fire
• Information can only travel in one direction in a synapse:

  • synaptic vesicles containing neurotransmitters are only present presynaptic membrane
  • the receptors for the neurotransmitters are only present in postsynaptic membrane
  • Diffusion of the neurotransmitters mean they can only go from high to low concentration, so only from pre to post
  • it is the binding of the neurotransmitter to the receptor which enables information to be transmitted to next neuron.
• Explain how an external factor that acts like an inhibitory transmitter effects synaptic transmission:

  • stimulation of postsynaptic receptors by an inhibitory neurotransmitter result in inhibition of the postsynaptic membrane
  • Zapurpain would make the post-synaptic cell less likely to fire
  • if inhibitory inputs are higher than excitatory they can cancel out excitation and inhibit an action potential, reducing brain activity may lead to reduced pain.