Posted in 2 SBI4U Biology

SBI4U Chemical Synapse Events

  • the action potential reaches the axon terminal
  • this triggers voltage-gated calcium channels to open allowing calcium ions to flow into the axon terminal (there must be a calcium pump to reverse this situation to reset things for the next round)
  • the calcium ions trigger the exocytosis of presynaptic vesicles that contain neurotransmitters like acetylcholine (acetylcholine is just one neurotransmitter, there are others like dopamine and serotonin)
  • the presynaptic vesicles fuse with the presynaptic membrane of the axon terminal and the neurotransmitters are excreted into the synaptic cleft
  • the neurotransmitters travel across the synaptic cleft and bind to ligand-gated sodium channels that are embedded in the post-synaptic membrane
  • the post-synaptic membrane may belong to another neuron, a muscle cell, a gland cell or any other effector cell in the body
  • when neurotransmitters have bound, the ligand-gated sodium channels open allowing sodium ions in the synaptic cleft to flow across the post-synaptic membrane
  • when enough sodium ions flood into the post-synaptic cell a new depolarization event will occur that will either trigger another action potential if the cell is a neuron, or the effect of that cell, like contracting if it’s a muscle cell

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