Process of synaptic transmission (excitation + inhibition)

• Synaptic Transmission -

  Nerve impulses travel down an axon. An action potential reaches the synaptic terminal and hits the vesicle on the pre-synaptic neuron enabling the neurotransmitter inside the vesicle to be released and fired into the synaptic cleft. Neurotransmitters bind with the receptors on the post-synaptic neuron and the neurotransmitters are taken up and the message is passed via electrical impulses.
• • Excitation = increases the positive charge of the post-synaptic neuron which increases the likelihood that the neuron will fire and pass on the electrical impulse (accelerator)
  • Inhibition = increases the negative charge of the post-synaptic neuron which decreases the likelihood that the neuron will fire and pass on the impulse (brakes)
  • Summation = combined effect of excitatory + inhibitory signals. If the net effect is inhibitory then it will be less likely to fire, if excitatory it will be more likely to fire.
• Explain why neurons can only transmit info in 1 direction at a synapse?

  • the synaptic vesicles containing the neurotransmitter are only present on/released from the presynaptic membrane
  • the receptors for the neurotransmitters are only present on the postsynaptic membrane
  • it is the binding of the neurotransmitter to the receptor which enables the signal/information to be passed/transmitted on (to the next neuron).
  • Diffusion of the neurotransmitters mean they can only go from high to low concentration, so can only travel from the presynaptic to the postsynaptic membrane.