Overview
This lecture explains the structure and function of synapses, their role in neural communication, and how neurotransmitters and drugs like cocaine affect this process.
Synapses and Neural Communication
- Synapses are microscopic junctions between two neurons enabling communication within the nervous system.
- The human brain has 100 billion neurons, each with 1,000–10,000 synapses, totaling up to 1,000 trillion synapses.
- Synapses can strengthen or weaken over time, enabling learning and memory.
Types of Synapses
- Electrical synapses use direct ion currents through gap junctions for instant, synchronized communication.
- Electrical synapses are fast but less controlled, mostly found in systems needing quick responses like the heart.
- Chemical synapses use neurotransmitters to send messages, allowing more precise and selective control.
Chemical Synapse Operation
- The presynaptic neuron sends a signal to the postsynaptic neuron across a synaptic cleft.
- Action potentials trigger voltage-gated calcium channels, causing neurotransmitter release from synaptic vesicles.
- Neurotransmitters cross the synaptic gap, bind to receptors, and can either excite or inhibit the postsynaptic neuron.
Excitatory vs. Inhibitory Neurotransmitters
- Excitatory neurotransmitters depolarize the postsynaptic neuron, increasing action potential likelihood.
- Inhibitory neurotransmitters hyperpolarize the postsynaptic neuron, decreasing action potential likelihood.
- One neuron can receive both excitatory and inhibitory signals, with the net effect determining its response.
Neurotransmitter Fate
- Neurotransmitters are quickly removed by reuptake, enzymatic breakdown, or diffusion after delivering their message.
Effects of Drugs on Synapses
- Drugs like cocaine block neurotransmitter reuptake, especially dopamine, serotonin, and norepinephrine.
- This causes neurotransmitter buildup, leading to temporary euphoria and, later, depletion and mood disturbances.
- Repeated drug use can reduce receptor numbers, causing dependency and dysfunction.
Key Terms & Definitions
- Synapse — the junction where two neurons communicate.
- Neuron — a nerve cell that transmits electrical and chemical signals.
- Action potential — an electrical impulse traveling down a neuron.
- Gap junction — direct connection between cell cytoplasms for electrical synapses.
- Neurotransmitter — chemical messenger released at synapses.
- Presynaptic neuron — neuron sending the signal.
- Postsynaptic neuron — neuron receiving the signal.
- Synaptic cleft — the tiny space between two communicating neurons.
- Excitatory neurotransmitter — increases likelihood of the postsynaptic neuron firing.
- Inhibitory neurotransmitter — decreases likelihood of the postsynaptic neuron firing.
- Reuptake — reabsorption of neurotransmitters by the sending neuron.
Action Items / Next Steps
- Review the previous episode to understand action potentials.
- Study neurotransmitter types and their specific effects on the nervous system.