Synaptic Transmission

• Process of Synaptic Transmission:

  1. Process begins in pre-synaptic neuron. Action potentials are sent down the axon until they reach pre-synaptic terminal
  2. Causes the neurotransmitters (stored in vesicles and only located in pre-synaptic neuron) to be released into the synaptic cleft
  3. Neurotransmitters diffuse across the synapse (from high to low concentration) and bind with their specific receptor sites (only present on post-synaptic neuron)
• Process of Synaptic Transmission:

  4. Once enough neurotransmitters have attached to receptor sites, there are two possible outcomes:

  > next neuron is ready to fire an impulse, depending on whether the neurotransmitter has an excitatory or inhibitory effect

  > neurotransmitters are recycled to be stored back in the vesicles in the pre-synaptic neuron in a process called reuptake
• Excitatory Neurotransmitter:

  > when the excitatory neurotransmitter binds to the post-synaptic receptors, the post-synaptic cell (next neuron) becomes positively charged

  > makes it more likely that the post-synaptic cell will fire so an impulse will travel down the axon - increases activity in CNS

  > example: adrenaline
• Inhibitory Neurotransmitter:

  > when the inhibitory neurotransmitter binds to the post-synaptic receptors, the post-synaptic cell (next neuron) becomes negatively charged

  > this prevents or reduces the likelihood that the post-synaptic cell will fire - decreases brain activity in the CNS

  > example: serotonin
• Summation:

  > occurs when the excitatory and inhibitory influences are added together

  > if the overall effect is mainly inhibitory, it reduces the likelihood that the neuron will fire an impulse down the post-synaptic neuron

  > if it is mainly excitatory, the impulse will fire down the post-synaptic neuron