CAM102 Lecture Notes - Lecture 35: Chemical Synapse, Axon Terminal, Membrane Potential
Learning Objectives
• Describe the parts of a synapse and how they influence neurotransmission: presynaptic
terminal, synaptic cleft, post synaptic side
• Name and describe the basic action of the main neurotransmitters used in the brain, spinal
cord and periphery
• Name and describe the function of four modulatory neurotransmitters in the brain
• Define ionotropic and metabotropic receptors
• Describe the properties of the blood-brain barrier and the cells which make it up
The Synapse
• At the axon terminals, APs release neurotransmitters, chemicals which diffuse to receptors in
the next cell
• These receptors are often ligand gated channels which can depolarise or hyperpolarise the
post-synaptic cell
• This produces a graded potential to influence the firing of the post-synaptic cell
Transmission
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• Neurotransmitters are released into enclosed space at the surface of another neuron, where
they activate receptors
• May alter membrane potential or trigger internal signalling
Why use chemical transmission?
• Tokens passed between cells
• Smart connectivity (both sides have a say in synaptic communication)
• Another good reason the brain is not a computer: non-linear and dynamic
• Neurons have multiple converging inputs and influences
A Synapse Has Three Components
Each is a potential site for regulation or drug interaction
Presynaptic Side
The neuron signals its activity by releasing molecules
Synaptic Cleft
The space molecules must cross, controlled by pre- and post-synaptic neurons, and a glial cell
Postsynaptic Side
The neuron chooses its response, by putting appropriate receptors into the membrane
Presynaptic Control
• Neurotransmitters are in the vesicles
• The presynaptic cell controls:
o What types of neurotransmitters it secrets
o How much
o How quickly
• Affected by feedback from the released neurotransmitter and the post synaptic cell
Synaptic Release
• The entry of calcium into the axon terminal activates complex protein machinery which:
o Moves a subset of vesicles to the membrane
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o Opens the vesicles (briefly or completely) at the presynaptic membrane
o Closes the vesicles or builds new ones from membrane
Synaptic Cleft
• Neurotransmitters attach to the receptors but need to be cleared away to end signalling
• In the cleft, transmitters can be broken down by enzymes, or taken up by glia or the
presynaptic terminal
• Glial cells can suck up neurotransmitters
Mopping Up
• Neurotransmitter transporters allow glia to control synapse dynamics and crosstalk between
synapses
• Uptake is so quick that photoreceptors signal bipolar cells by stopping release of glutamate
Postsynaptic Side
• The postsynaptic neuron chooses the effect of the NT by the receptors placed in the
membrane
• Elaborate postsynaptic complexes permit regulation of the number and type of receptors
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Document Summary
Transmission: neurotransmitters are released into enclosed space at the surface of another neuron, where they activate receptors, may alter membrane potential or trigger internal signalling. Smart connectivity (both sides have a say in synaptic communication: tokens passed between cells, another good reason the brain is not a computer: non-linear and dynamic, neurons have multiple converging inputs and influences. Each is a potential site for regulation or drug interaction. The neuron signals its activity by releasing molecules. The space molecules must cross, controlled by pre- and post-synaptic neurons, and a glial cell. The neuron chooses its response, by putting appropriate receptors into the membrane. Presynaptic control: neurotransmitters are in the vesicles, the presynaptic cell controls, what types of neurotransmitters it secrets, how much, how quickly, affected by feedback from the released neurotransmitter and the post synaptic cell. Synaptic cleft: neurotransmitters attach to the receptors but need to be cleared away to end signalling.
