The Process of Synaptic Transmission
Synaptic transmission is the process by which neighbouring neurons communicate with
each other by sending chemical messages across the gap (the synapse) from one neuron
(the presynaptic neuron) to another the postsynaptic neuron).
1. The dendrites of neurons receive information from sensory receptors or other
neurons.
Once information has arrived at the axon, the inside of the neuron becomes
positively charged. The information travels down its length in the form of an
electrical signal known as an action potential.
(When in a resting state, neurons are negatively charged.)
Action potential = surge of positive charge and the electrical signal travelling along
the axon
2. When the electrical impulse (i.e., action potential) reaches the end of the neuron
(the presynaptic terminal) it triggers the release of neurotransmitters from tiny
sacs called synaptic vesicles (through a process called exocytosis).
3. Once the neurotransmitter diffuses across the synaptic cleft, it binds to its
specialised post synaptic receptor site (i.e., on the dendrites of the next neuron).
4. The binding of neurotransmitters to specific receptors may influence the post-
synaptic neuron in either an inhibitory or excitatory way. Whether the post-
synaptic neuron fires an action potential is decided by the process of summation.
The excitatory and inhibitory influences of neurotransmitters are summed.
If the net effect on the post-synaptic neuron is inhibitory, hyperpolarisation
occurs, meaning the post-synaptic neuron becomes more negatively charged and
the neuron will be less likely to ‘fire’ an action potential.
If the net effect is excitatory, depolarisation occurs, meaning the post-synaptic
neuron becomes more positively charged and the neuron will be more likely to ‘fire’
an action potential.
5. This whole process of synaptic transmission takes only a fraction of a second, with
the effects terminated at most synapses by a process called ‘re-uptake’. The
neurotransmitter is taken up again by the presynaptic neuron, where it is stored
and made available for later release (a sort of recycling programme).
Summarised:
, 1. Action potential reaches presynaptic terminal
2. Neurotransmitters released from synaptic vesicles into synapse and diffuse
across gap
3. Neurotransmitters bind to specialised postsynaptic receptor sites
4. The excitatory and inhibitory neurotransmitters are summed (the net effect will
determine whether the postsynaptic neuron will fire)
5. Process ends with ‘reuptake’ (neurotransmitter reabsorbed by presynaptic neuron,
where it is stored and made available for later release)
Electrical transmission – The Firing of a Neuron
- When a neuron is in a resting state the inside of the cell becomes negatively
charged compared to the outside.
- When a neuron is activated by a stimulus, the inside of the cell becomes positively
charged for a split second causing an action potential to occur.
- This creates an electrical impulse that travels down the axon towards the end of
the neuron.
Neurotransmitters
- Neurotransmitters are chemicals that diffuse across the synapse to the next
neuron.
- Once a neurotransmitter crosses the gap, it is taken up by a post synaptic receptor
site on the dendrites of the next neuron. Here, the chemical message is converted
back into an electrical impulse and the process of transmission begins again in
this other neuron.
- Several dozen types of neurotransmitter have been identified in the brain (as well as
in the spinal cord and some glands) such as dopamine, serotonin, and GABA.
Synaptic transmission is the process by which neighbouring neurons communicate with
each other by sending chemical messages across the gap (the synapse) from one neuron
(the presynaptic neuron) to another the postsynaptic neuron).
1. The dendrites of neurons receive information from sensory receptors or other
neurons.
Once information has arrived at the axon, the inside of the neuron becomes
positively charged. The information travels down its length in the form of an
electrical signal known as an action potential.
(When in a resting state, neurons are negatively charged.)
Action potential = surge of positive charge and the electrical signal travelling along
the axon
2. When the electrical impulse (i.e., action potential) reaches the end of the neuron
(the presynaptic terminal) it triggers the release of neurotransmitters from tiny
sacs called synaptic vesicles (through a process called exocytosis).
3. Once the neurotransmitter diffuses across the synaptic cleft, it binds to its
specialised post synaptic receptor site (i.e., on the dendrites of the next neuron).
4. The binding of neurotransmitters to specific receptors may influence the post-
synaptic neuron in either an inhibitory or excitatory way. Whether the post-
synaptic neuron fires an action potential is decided by the process of summation.
The excitatory and inhibitory influences of neurotransmitters are summed.
If the net effect on the post-synaptic neuron is inhibitory, hyperpolarisation
occurs, meaning the post-synaptic neuron becomes more negatively charged and
the neuron will be less likely to ‘fire’ an action potential.
If the net effect is excitatory, depolarisation occurs, meaning the post-synaptic
neuron becomes more positively charged and the neuron will be more likely to ‘fire’
an action potential.
5. This whole process of synaptic transmission takes only a fraction of a second, with
the effects terminated at most synapses by a process called ‘re-uptake’. The
neurotransmitter is taken up again by the presynaptic neuron, where it is stored
and made available for later release (a sort of recycling programme).
Summarised:
, 1. Action potential reaches presynaptic terminal
2. Neurotransmitters released from synaptic vesicles into synapse and diffuse
across gap
3. Neurotransmitters bind to specialised postsynaptic receptor sites
4. The excitatory and inhibitory neurotransmitters are summed (the net effect will
determine whether the postsynaptic neuron will fire)
5. Process ends with ‘reuptake’ (neurotransmitter reabsorbed by presynaptic neuron,
where it is stored and made available for later release)
Electrical transmission – The Firing of a Neuron
- When a neuron is in a resting state the inside of the cell becomes negatively
charged compared to the outside.
- When a neuron is activated by a stimulus, the inside of the cell becomes positively
charged for a split second causing an action potential to occur.
- This creates an electrical impulse that travels down the axon towards the end of
the neuron.
Neurotransmitters
- Neurotransmitters are chemicals that diffuse across the synapse to the next
neuron.
- Once a neurotransmitter crosses the gap, it is taken up by a post synaptic receptor
site on the dendrites of the next neuron. Here, the chemical message is converted
back into an electrical impulse and the process of transmission begins again in
this other neuron.
- Several dozen types of neurotransmitter have been identified in the brain (as well as
in the spinal cord and some glands) such as dopamine, serotonin, and GABA.
