Synapses

Synapses

Neuronal Synapse:

• A (neuronal) synapse is the junction between two neurones
• The neurones do not touch
• The neurone before the is the presynaptic neurone
• The neurone after the syapse is the postsynaptic neurone

Cholinergic Synapse:

• Uses the neurotransmitter acetylcholine (among many other neurotransmitters)
• Transmission across a cholinergic synapse -
  • action potential arrives at synaptic knob
  • causes gated calcium ion channel proteins to open
  • allows influx of calcium ions into presynaptic neurone
  • calcium ions cause neurotransmitter vesicles to move and fuse with the presynaptic membrane
  • acetylcholine diffuses across synaptic gap
  • acetylcholine binds to receptor proteins on postsynaptic membrane
  • causes gated sodium ion channel proteins to open
  • allows influx of sodium ions
  • depolarisation occurs if threshold is reached
  • action potential generated and travels along postsynaptic neurone
  • synapse restored to transmit another nerve impulse
  • acetylcholineterase (enzyme) hydrolyses acetylcholine to release it from the receptor protein binding sites
  • breakdown products returned into synaptic knob
  • acetylchloine reforms into vesicles
  • calcium…