Synaptic transmission
Synaptic transmission
Objectives:
To describe the process of electrical transmission between neurones.
To highlight the differences between chemical and electrical transmission.
To describe the process of chemical transmission.
To explain the electrical events associated with chemical transmission
ELECTRICAL TRANSMISSION Direct flow of ions from one neurone to another (direct influence of electric current from one to another) E.g. gap junction
Gap junction: directly connects the cytoplasm of two cells allows various molecules and ions to pass freely between cells, allow action potentials to spread.
They are modulated by pH, neurotransmitters and [Ca2+].
CHEMICAL NEUROTRANSMISSION Neurotransmitter substance released from presynaptic cell, diffuses across synaptic cleft, produces effect on postsynaptic neurone e.g. central synapse
1.Amino acid and amine neurotransmitters are synthesised in the axon terminal Peptide neurotransmitters are formed in the cell body
2. Neurotransmitter is taken up into vesicles by transporters
3. Synaptic release occurs due to a rise in intracellular calcium. Vesicles discharge neurotransmitter into the synaptic cleft and are recycled.
4. Neurotransmitter binds to receptor molecules in the postsynaptic membrane. Receptor activation induces changes in postsynaptic cell.
5. Neurotransmitter is either broken down in the synaptic cleft, undergoes reuptake into the terminal, or diffuses away from the synaptic region.
Electrical synapses
Chemical synapses
Distance between pre- and post-synaptic cell membranes
3.5 nm
30-50 nm
Cytoplasmic continuity between pre- and post-synaptic cell membranes
Yes
No
Ultrastructural components
Gap junction channels
Presynaptic active zones and vesicles, postsynaptic receptors
Agent of transmission
Ionic current
Chemical transmitter
Synaptic delay
Virtually absent
At least 0.3 ms, usually 1-5 ms
Direction of transmission
Objectives:
To describe the process of electrical transmission between neurones.
To highlight the differences between chemical and electrical transmission.
To describe the process of chemical transmission.
To explain the electrical events associated with chemical transmission
ELECTRICAL TRANSMISSION Direct flow of ions from one neurone to another (direct influence of electric current from one to another) E.g. gap junction
Gap junction: directly connects the cytoplasm of two cells allows various molecules and ions to pass freely between cells, allow action potentials to spread.
They are modulated by pH, neurotransmitters and [Ca2+].
CHEMICAL NEUROTRANSMISSION Neurotransmitter substance released from presynaptic cell, diffuses across synaptic cleft, produces effect on postsynaptic neurone e.g. central synapse
1.Amino acid and amine neurotransmitters are synthesised in the axon terminal Peptide neurotransmitters are formed in the cell body
2. Neurotransmitter is taken up into vesicles by transporters
3. Synaptic release occurs due to a rise in intracellular calcium. Vesicles discharge neurotransmitter into the synaptic cleft and are recycled.
4. Neurotransmitter binds to receptor molecules in the postsynaptic membrane. Receptor activation induces changes in postsynaptic cell.
5. Neurotransmitter is either broken down in the synaptic cleft, undergoes reuptake into the terminal, or diffuses away from the synaptic region.
Electrical synapses
Chemical synapses
Distance between pre- and post-synaptic cell membranes
3.5 nm
30-50 nm
Cytoplasmic continuity between pre- and post-synaptic cell membranes
Yes
No
Ultrastructural components
Gap junction channels
Presynaptic active zones and vesicles, postsynaptic receptors
Agent of transmission
Ionic current
Chemical transmitter
Synaptic delay
Virtually absent
At least 0.3 ms, usually 1-5 ms
Direction of transmission