Synapses

• Synaptic cleft

  Minute gaps across which neurotransmitter substances diffuse
• Propagation of an action potential (AP)

  1. AP is propagated along neuron

  2. Arrives at membrane/knob

  3. Presynaptic membrane depolarizes

  4. Voltage gated Ca2+ ion channels open

  5. Ca2+ induces vesicles to release neurotransmitter via exocytosis
• Vesicles containing neurotransmitter

  • Located close to presynaptic membrane
  • Release neurotransmitter via exocytosis
• Neurotransmitter quickly diffuses across synaptic cleft
• Ligand gated receptor

  Receptor on postsynaptic membrane that binds neurotransmitter
• Neurotransmitter binding response

  1. Neurotransmitter binds to receptor

  2. Channels undergo conformational change

  3. Channels open
• Na+ enters the postsynaptic neuron down its electrochemical gradient
• Cholinergic synapses 

  Where two neurons meet, they do not actually come into physical contact with each other 

  • Very small hap, known as the synaptic cleft separates them 
  • Ends of two neurons along the synaptic cleft form a synapse