HMB201H1 Lecture Notes - Lecture 6: Electrical Synapse, Autonomic Nervous System, Gap Junction

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15 Nov 2012
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Lecture 6
Membrane potential govern the ability to be able to move signals across the body: you
can move them in a more public way like endocrine way or nervous system which is
more private!
We will start from the synapse onwards then leads to the autonomic nervous system
1) Synapse
2) Neurotransmitter
3) Receptor types
4) Autonomic nervous system
Signal transmission, electrical and chemical synapses:
Action potential comes down from the axon and reaches the electrical synapse where
you have gap junctions. This is less common in animals but it is important for
communication. You will find these in certain areas in nervous system in the brain
Presyanptic neuron depolarized and been propagated down the action potential and
has ions flux or pass through the gap junction with electrical signal and goes through
the postsynaptic neuron
Now fine, we get why we have electrical synapse, then why bother with the electrical
synapse?
Chemical synapse has the ability to amplilify or diminishes a chemical signal
the chemical that are released from presyanptic cam amplify or diminish to the
post synaptic
Electrical synapse Chemical synapse
- Direct flow of electric current from one cell
to another through gap junctions:
- Fast
- Bi-directional
- Postsynaptic signal is similar to presynaptic
signal
- excitatory ( always gonna be like that,
always there will be a change in ions)
- Secrete neurotransmitter molecules that activate -
receptors:
- Slower
- Unidirectional
- Pre and postsynaptic signals can differ
- Excitatory or inhibitory (either ions will change or it
will be inhibited)
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Chemical synapsing:
Action potential bringing down an electrical current all the way down the presyanptic
cell.
What happens? Voltage gated calcium ions, what is the key for synapse to release the
neurotransmitter?
1) The voltage gated calcium channels
2) The presence of vesicles with important neurotransmitter released in the
presyanptic cleft.
Synaptic vesicles come down the axon and transported down the axon terminal. They are
independent from the action potential!!! They weren’t there at first, they appear after.
Invasion of calcium because of the change in the membrane potential at the axon bud and
this invasion signals to the synaptic vesicles and bind to the docking protein which fuses
with cell membrane then exocytose to the synaptic cleft and after there are ligand gated
channels that bind with neurotransmitter and induces a response. That’s why calcium is
involved. (REMEMBER, CHEMICAL SINGNAL ALWAYS HAS A LIGAND)
Transmission of signal at the chemical synapse:
- Postsynaptic cells have specific receptors for neurotransmitter! SPECIFIC!
- Neurotransmitter will alter the membrane potential of the postsynaptic cell and
this changes the membrane channel of this postsynaptic
Response of postsynaptic cell dependent on:
- Density of receptors on postsynaptic cell (how they are there)
- Amount of neurotransmitter released which is determined by the frequency of
action potential ( how much neurotransmitter are released)
- The rate of removal (how long it takes)
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