Lecture Notes on Synapses and Neural Communication

Introduction to Synapses

• Synapses are the junctions between neurons.
• They are essential in transforming the nervous system from a structure to a functioning system.
• Synapse means "to clasp or join" in Greek.

Function of Synapses

• Convert electrical signals into different types of signals to communicate between neurons.
• Human brain has 100 billion neurons with 1000 to 10,000 synapses each, totaling 100 to 1,000 trillion synapses.
• Synapses adapt and change in response to neuron firing patterns, facilitating learning and memory.

Types of Synapses

• Electrical Synapses:
  • Transmit signals directly via ion current through gap junctions.
  • Faster, used for quick communication, e.g., in heart muscles for coordinated contractions.
  • Lack control, so not all synapses are electrical.
• Chemical Synapses:
  • Slower but more precise; use neurotransmitters to send messages.
  • Convert signals from electrical to chemical and back, allowing for control and modulation.

Components of Chemical Synapses

• Presynaptic Neuron: Sends signals through the presynaptic terminal.
  • Contains synaptic vesicles with neurotransmitters.
• Postsynaptic Neuron: Receives neurotransmitters at receptor sites on dendrites or cell body.
• Synaptic Cleft: Small gap between neurons where neurotransmitters diffuse.

Process of Chemical Synapse Transmission

• Action potential triggers calcium channels to release calcium ions.
• Synaptic vesicles fuse with cell membrane, releasing neurotransmitters.
• Neurotransmitters bind to receptors, converting chemical signals back to electrical signals.
• Excitatory Neurotransmitters: Depolarize postsynaptic neurons, making action potential more likely.
• Inhibitory Neurotransmitters: Hyperpolarize neurons, reducing likelihood of firing.

Neurotransmitters

• Over 100 types, regulate various body functions and emotions.
• Neurotransmitters are quickly degraded or reabsorbed after use.
• Reuptake is a process where neurotransmitters are absorbed back by the presynaptic neuron.

Impact of Drugs on Synapses

• Drugs can disrupt neurotransmitter balance.
• E.g., Cocaine blocks reuptake of serotonin, dopamine, and norepinephrine, causing euphoria but eventual neurotransmitter depletion.
• Prolonged drug use alters synapse function and receptor availability, leading to addiction.

Conclusion

• Synapses are crucial for effective communication in the nervous system, knowing when to excite or inhibit.
• Healthy synaptic function maintains balance and proper neural communication.
• Dysfunction in synapse activity, as seen with drugs, illustrates the importance of maintaining natural neurotransmitter balance.