Synaptic transmission

• Synaptic transmission

  Basic mechanism of communication between neurons
• Electric impulses cannot ‘jump’ across synapses
• Synaptic transmission process

  1. Electrical impulses arrive at presynaptic neuron

  2. Neurotransmitters released from vesicles

  3. Neurotransmitters diffuse across synaptic cleft

  4. Bind with receptor molecule in postsynaptic membrane

  5. Stimulates postsynaptic neuron to generate electrical impulse
• Neurotransmitters

  Chemical messengers released during synaptic transmission
• Neurotransmitters are then destroyed or recycled to prevent continued stimulation of the second neuron
• Continued stimulation of the second neuron could cause repeat impulses to be sent
• mechanism of synaptic transmission

  
• Neurotransmitters

  Over 40 different known neurotransmitters
• Acetylcholine (ACh)

  One of the key neurotransmitters used throughout the nervous system
• Cholinergic synapses

  Synapses that use the neurotransmitters ACh
• Detailed process of synaptic transmissions using ACh

  1. Arrival of action potential

  2. Depolarization of the membrane

  3. Calcium ion channel proteins open

  4. Calcium ions diffuse into cytoplasm

  5. ACh-containing vesicles fuse with presynaptic membrane

  6. ACh molecules released into postsynaptic cleft

  7. ACh molecules bind to receptor proteins

  8. Confirmational change in receptor protein

  9. Sodium ions diffuse into cytoplasm

  10. Depolarization of the postsynaptic membrane

  11. ACh molecules broken down and recycled
• Calcium ions

  • Diffuse down an electrochemical gradient from high concentration to low concentration
• ACh molecules

  • Diffuse across the synaptic cleft
  • Temporarily bind to receptor proteins
• Sodium ions

  • Cause depolarization of the postsynaptic membrane
  • Re-start the electrical impulse
• Acetylcholinesterase


  Enzyme that catalyzes the hydrolysis of ACh molecules into acetate and choline
• The choline is absorbed back into the presynaptic membrane and reacts with acetyl coenzyme A to form ACh
• This entire sequence takes between 5 - 10ms
• Synaptic transmission using acetylcholine