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Neurotransmitters/Neurotransmission

Neurotransmission and Its Regulation

Neurotransmission is a complex and highly regulated process that allows neurons to communicate with each other and with target cells, such as muscles or other neurons. This lecture will cover the fundamentals of neurotransmission and the mechanisms that regulate it.

Key Concepts

1. Neurotransmission:

  • Definition: Neurotransmission is the process by which neurons transmit signals or information to other neurons, muscles, or glands via chemical messengers called neurotransmitters.

  • Neurons: Neurons are the specialized cells responsible for transmitting electrical and chemical signals in the nervous system.

  • Synapses: The junction between two neurons, or between a neuron and its target cell (e.g., muscle or gland), is called a synapse. There are two types of synapses: chemical synapses and electrical synapses.

2. Chemical Synapses:

  • Neurotransmitters: Neurons communicate at chemical synapses by releasing neurotransmitters from synaptic vesicles into the synaptic cleft. Common neurotransmitters include acetylcholine, serotonin, dopamine, and gamma-aminobutyric acid (GABA).

  • Presynaptic Neuron: The neuron sending the signal is the presynaptic neuron. It contains synaptic vesicles filled with neurotransmitters.

  • Postsynaptic Neuron: The neuron receiving the signal is the postsynaptic neuron. Neurotransmitters bind to receptors on the postsynaptic neuron, leading to changes in membrane potential and signal transmission.

3. Regulation of Neurotransmission:

  • Neurotransmitter Release:

    • Voltage-Gated Calcium Channels: Action potentials in the presynaptic neuron open voltage-gated calcium channels, allowing calcium ions to enter the neuron. Calcium triggers the fusion of synaptic vesicles with the presynaptic membrane, leading to neurotransmitter release.

  • Neurotransmitter Reception:

    • Receptor Binding: Neurotransmitters bind to specific receptors on the postsynaptic membrane. This binding can either excite (depolarize) or inhibit (hyperpolarize) the postsynaptic neuron.

  • Termination of Neurotransmission:

    • Reuptake: Neurotransmitters can be taken back up into the presynaptic neuron by transporters, such as the serotonin reuptake transporter (SERT).

    • Enzymatic Degradation: Enzymes in the synaptic cleft, like acetylcholinesterase, can break down neurotransmitters into inactive metabolites.

    • Diffusion: Neurotransmitters can simply diffuse away from the synapse.

4. Neuromodulation:

  • Definition: Neuromodulators are signaling molecules that can modify the strength or efficacy of synaptic transmission without directly causing postsynaptic potentials. Examples include neuropeptides and endocannabinoids.

  • Long-Term Potentiation (LTP): LTP is a cellular mechanism involved in learning and memory. It strengthens synaptic connections between neurons by enhancing postsynaptic responses to neurotransmitters.

Importance in Physiology

  • Central Nervous System (CNS) Function: Neurotransmission is essential for all aspects of CNS function, including sensory perception, motor control, emotion, and cognition.

  • Learning and Memory: Understanding the regulation of neurotransmission is crucial for studying learning and memory processes.

Clinical Relevance

  • Neurological Disorders: Dysregulation of neurotransmission is implicated in various neurological disorders, including Parkinson's disease, Alzheimer's disease, depression, and schizophrenia. Medications used to treat these conditions often target neurotransmitter systems.

  • Drug Addiction: Many drugs of abuse, such as opioids, cocaine, and amphetamines, affect neurotransmission and can lead to addiction.

Conclusion

Neurotransmission is a fundamental process in the nervous system, enabling communication between neurons and the transmission of information. Its regulation is critical for normal brain function and has important implications for neurological and psychiatric disorders.

References

  1. Kandel, E. R., Schwartz, J. H., & Jessell, T. M. (2000). Principles of Neural Science (4th ed.). McGraw-Hill.

  2. Südhof, T. C. (2013). Neurotransmitter release: the last millisecond in the life of a synaptic vesicle. Neuron, 80(3), 675-690.

  3. Zucker, R. S., & Regehr, W. G. (2002). Short-term synaptic plasticity. Annual Review of Physiology, 64(1), 355-405.
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