Nerve conduction - Synapse (2)

Question 1

What happens during the release of neurotransmitter?

Answer 1

Vesicles are “docked” on release zone of presy membrane on protein sites. Ca+ is in the highest concentration outside of neuron, and the release zone contains voltage sensitive Ca+ channels. Action potential arrives at the terminal button (depolarizes) and Ca+ channels are opened. Once that happens, Ca+ enters neuron by diffusion and electrostatic forces and binds with the protein sites where vesicles are docked, causing the proteins to move apart, creating a fusion pore in the membranes through with the NT is released

Question 2

What happens after the NT is released?

Answer 2

Ca+ transporters in the membrane later remove Ca+ (similar to Na+ transporters). The vesicle membrane fuses with terminal button membrane. The TB membrane “pinches off” at the junction of the axon and TB, migrate to a fuse with the cisternae, which produces new vesicles - takes from few seconds to few minutes OR “kiss and run”

Question 3

Activation of Postsynaptic receptors…

Answer 3

NT binds to postsy receptor site and causes neurotransmitter dependent ion channels to open, changing the membrane potential (i.e., electrical charge). Ion channels open by direct or indirect method

Question 4

What happens when ion channels open by a direct method?

Answer 4

• Direct – or Ionotropic receptor - ion channel has nt binding site. When nt attaches to binding site, channel opens.

Question 5

What happens when ion channels open by an indirect method?

Answer 5

• Indirect – or Metabotropic receptor – nt receptor activates G protein. Part of G protein called alpha subunit breaks off:
  a. attaches to binding site on ion channel and it opens or
  b. activates an enzyme in the membrane which causes production of chemical in cytoplasm called second messenger. Sm causes ion channels to open and also causes biochemical and structural changes in nucleus and other parts of cell, including affecting gene expression.