Overview
This lecture explains the process of synaptic transmission, detailing how neurons communicate at synapses by releasing and receiving neurotransmitters.
Synaptic Transmission Process
- Synaptic transmission is how neurons communicate at synapses, the junctions between them.
- An action potential travels down the axon to the terminal button (axon terminal).
- Calcium gates open at the terminal button, allowing calcium ions to enter the neuron.
- Calcium binds to vesicles containing neurotransmitter molecules in the terminal button.
- Calcium-bound vesicles move to the presynaptic membrane and release neurotransmitter into the synaptic cleft (synaptic space).
- Neurotransmitter diffuses across the synaptic cleft.
- Some neurotransmitter returns to the presynaptic cell, signaling it to stop releasing more transmitter.
- Most neurotransmitter binds to receptors on the postsynaptic cell, transmitting the signal.
Lock and Key Mechanism
- Neurotransmitter binding to postsynaptic receptors is a lock and key mechanism.
- The receptor is the "lock" and the neurotransmitter is the "key"; their shapes and charges must match for binding.
Effects on Postsynaptic Cell
- Binding can excite the postsynaptic cell, increasing voltage (excitatory postsynaptic potential, EPSP).
- Binding can inhibit the postsynaptic cell, decreasing voltage (inhibitory postsynaptic potential, IPSP).
- Binding can modulate the postsynaptic cell, altering its sensitivity to future signals.
Removal of Neurotransmitter
- Neurotransmitter is removed by reuptake (about 70%), recycling it back into the presynaptic neuron.
- Neurotransmitter can also be metabolized (broken down) by chemicals in the synapse.
Importance of Synaptic Transmission
- Synaptic transmission, together with action potentials, enables all functions of the nervous system including perception, emotion, thought, and movement.
Key Terms & Definitions
- Synapse — junction between two neurons where communication occurs.
- Action potential — electrical impulse that travels down the axon.
- Terminal button — end of the axon where neurotransmitter release occurs.
- Vesicle — tiny sac containing neurotransmitter molecules.
- Neurotransmitter — chemical messenger transmitting signals between neurons.
- Synaptic cleft — the small gap between pre- and postsynaptic cells.
- Presynaptic membrane — membrane at the end of the transmitting neuron.
- Postsynaptic receptor — protein on receiving neuron's membrane that binds neurotransmitters.
- Excitatory postsynaptic potential (EPSP) — increase in postsynaptic cell voltage.
- Inhibitory postsynaptic potential (IPSP) — decrease in postsynaptic cell voltage.
- Reuptake — recycling of neurotransmitter back into the presynaptic cell.
- Metabolization — chemical breakdown of neurotransmitter in the synapse.
Action Items / Next Steps
- Review diagrams of the synaptic transmission process.
- Learn key terms and their definitions for the next quiz.