Cholinergic Synapses

• One of the key neurotransmitters used throughout the nervous system is acetylcholine (ACh). Synapses that use the neurotransmitter ACh are known as cholinergic synapses
• What causes depolarization of the presynaptic membrane?


  The arrival of an action potential
• What happens when the presynaptic membrane depolarizes?


  Voltage-gated calcium ion channel proteins open
• How do calcium ions move during synaptic transmission?


  They diffuse down an electrochemical gradient from high to low concentration
• What is the role of calcium ions (Ca2+) in the synaptic knob?


  They stimulate ACh-containing vesicles to fuse with the presynaptic membrane
• What process releases ACh molecules into the synaptic cleft?


  Exocytosis
• What happens to ACh molecules after they are released into the synaptic cleft?


  They diffuse across the cleft and bind to cholinergic receptors
• What effect does ACh binding to cholinergic receptors have on the postsynaptic membrane?


  It causes sodium ion channels to open
• What occurs when sodium ions diffuse into the cytoplasm of the postsynaptic neurone?


  Depolarization of the postsynaptic membrane occurs
• What is the significance of reaching the threshold in the postsynaptic neurone?


  It re-starts the electrical impulse
• What happens to ACh molecules after they have acted on the postsynaptic membrane?


  They are broken down and recycled
• Why is it important to break down ACh in the synaptic cleft?


  To prevent permanent depolarization of the postsynaptic membrane
• Which enzyme catalyzes the hydrolysis of ACh molecules?

  Acetylcholinesterase
• What are the products of ACh hydrolysis?


  Acetate and choline
• What happens to choline after ACh is hydrolyzed?


  It is absorbed back into the presynaptic membrane
• What does choline react with to form ACh again?


  Acetyl coenzyme A
• What happens to ACh after it is formed in the presynaptic membrane?


  It is packaged into presynaptic vesicles
• When is ACh ready to be used again?


  When another action potential arrives
• Cholinergic Synapses:

  A) Action potential

  B) depolarising

  C) Calcium ion

  D) open

  E) calcium

  F) in

  G) presynaptic vesicles

  H) ACh

  I) ACh

  J) Synaptic cleft

  K) ACh

  L) Receptor

  M) open

  N) sodium ions

  O) depolarised

  P) ACh

  Q) Acetate

  R) Choline

  S) Acetylecholinerase

  T) Choline

  U) ACh