L1.1.4.2: Transmission of Signal (Conductivity)

• TRANSMISSION OF SIGNAL (conductivity)

  ● An electrochemical event

  ○ ELECTRICAL — transmission down the length of the neuron’s axon

  ○ CHEMICAL — transmission to the next neuron
• TRANSMISSION OF SIGNAL (conductivity)

  1. Action potential arrives
  2. Vesicle fuses with plasma membrane
  3. Neurotransmitter is released into the synaptic cleft
  4. Neurotransmitter binds to a receptor on the receiving neuron’s membrane
  5. Ion channel opens
  6. Ion channel closes
• (1) Action potential arrives

  ■ When the action potential reaches the axon terminal, the electrical charge opens calcium channels
• (2) Vesicle fuses with plasma membrane

  ■ Calcium ions cause the tiny vesicles containing the neurotransmitter chemical to fuse with the axonal membrane
• (3) Neurotransmitter is released into the synaptic cleft

  ■ The entry of calcium into the axon terminal causes pore-like openings to form, releasing the neurotransmitter into the synaptic cleft by exocytosis
• (4) Neurotransmitter binds to a receptor on the receiving neuron’s membrane

  ■ The neurotransmitter molecules diffuse across the synaptic cleft and bind to receptors on the membrane of the next neuron
• (5) Ion channel opens

  ■ If enough neurotransmitter is released, a graded potential will be generated (in this instance, by sodium entry)

  ■ Eventually, an action potential will occur in the neuron beyond the synapse
• (6) Ion channel closes

  ■ Neurotransmitter is broken down and released

  ■ The electrical changes prompted by neurotransmitter binding are brief

  ■ Because neurotransmitter is quickly removed from the synaptic cleft by either (1) reuptake or (2) enzymatic activity