Overview
This lecture explains synaptic transmission, the process by which neurons communicate through chemical signals at the synapse.
Synapse Structure and Function
- Most neuron communication occurs at synapses, specialized contact points between two neurons.
- A synapse involves two neurons separated by a tiny gap called the synaptic cleft (less than 40 nanometers wide).
- The neuron sending the signal is the presynaptic neuron; the receiving neuron is the postsynaptic neuron.
Neurotransmitter Release and Reception
- Neurotransmitters are chemical messengers stored in vesicles within the presynaptic neuron.
- When an action potential (electrical signal) arrives at the presynaptic neuron, it causes vesicles to fuse with the membrane and release neurotransmitters into the synaptic cleft.
- Released neurotransmitters bind to receptors on the postsynaptic neuron’s membrane.
- This binding can either increase or decrease the likelihood that the postsynaptic neuron will fire an action potential.
Clearing Neurotransmitters from the Synaptic Cleft
- Neurotransmitters in the cleft are removed by diffusion (drifting away), reuptake (taken back into the presynaptic neuron), or enzymatic breakdown.
- Reuptake allows neurotransmitters to be recycled for future use.
- Enzymes can break down neurotransmitters, and their parts can be recycled to make new neurotransmitters.
Key Terms & Definitions
- Synapse — the junction between two neurons where communication occurs.
- Synaptic cleft — the microscopic gap separating presynaptic and postsynaptic neurons.
- Presynaptic neuron — the neuron sending the signal.
- Postsynaptic neuron — the neuron receiving the signal.
- Neurotransmitter — chemical messenger released into the synaptic cleft to transmit signals.
- Vesicle — small sac in the presynaptic neuron containing neurotransmitters.
- Action potential — an electrical signal that triggers neurotransmitter release.
- Reuptake — process where neurotransmitters are taken back into the presynaptic neuron.
- Enzymatic breakdown — enzymes degrade neurotransmitters in the synaptic cleft.
Action Items / Next Steps
- Review the steps of synaptic transmission for understanding.
- Learn the definitions of key terms and processes described.