PHYS20008 Lecture Notes - Lecture 6: Axon Hillock, Depolarization, Axon Terminal
21 Jun 2018
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Lecture 6: Synaptic transmission
What we have gathered so far is that action potentials begin at the axon hillock and travel
down the axon through refractory periods of opening and closing voltage-gated Na+ and K+
channels. At the axon terminals of a neuron is where the action potential is released- rightly
also called the ‘output zone’ for this reason.
At the terminal, there are synaptic vesicles full of neurotransmitters that are released into
the synapse and then received by the postsynaptic cell.
This is where the voltage-gated Ca 2+
channels come into play:
Neuron to neuron:
1) An action potential depolarises the axon terminal
2) The depolarisation opens voltage-gated Ca2+ channels and Ca2+ enters the cell
3) Calcium triggers exocytosis of synaptic vesicle contents
4) Neurotransmitter diffuses across the synaptic cleft and binds with receptors on the
postsynaptic cell
5) Neurotransmitter binding initiates a response in the postsynaptic cell.
*Removing/recycling neurotransmitters from synapse involves the pre-synaptic cell transporting
them back into the cell. This is called reuptake.
Types of neurotransmitters:
There are 2 general types of neurotransmitters that interact with a receptor and the post-
synaptic cell:
1) Excitatory: Excites the next cell; leads to the depolarisation of the target cell
2) Inhibitory: Inhibits a signal to the next cell; hyperpolarisation in target cell (further
from threshold)
*Cl- is important as it buffers membrane potential away from threshold
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Document Summary
What we have gathered so far is that action potentials begin at the axon hillock and travel down the axon through refractory periods of opening and closing voltage-gated na+ and k+ channels. At the axon terminals of a neuron is where the action potential is released- rightly also called the output zone" for this reason. At the terminal, there are synaptic vesicles full of neurotransmitters that are released into the synapse and then received by the postsynaptic cell. *removing/recycling neurotransmitters from synapse involves the pre-synaptic cell transporting them back into the cell. There are 2 general types of neurotransmitters that interact with a receptor and the post- synaptic cell: excitatory: excites the next cell; leads to the depolarisation of the target cell. Inhibitory: inhibits a signal to the next cell; hyperpolarisation in target cell (further from threshold) *cl- is important as it buffers membrane potential away from threshold.
