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Track 11: Cellular Neuroscience

Track 11: Cellular Neuroscience

Sub Tracks: The Functional Units of the Nervous System, Ion Channels and Membrane Potential, Synaptic Transmission, Glial Cells and Their Roles,Cellular Mechanisms of Learning and Memory, Excitability and Ion Homeostasis, Neural Circuitry and Connectivity

Cellular Neuroscience is a branch of neuroscience that focuses on the study of the cells of the nervous system, particularly neurons and glial cells, and how they function, communicate, and contribute to higher brain functions. It deals with the physiological mechanisms that govern cellular activity within the nervous system, including the electrical properties of neurons, synaptic transmission, and the cellular changes that occur during learning, memory, and disease processes.

1. Neurons: The Functional Units of the Nervous System

Structure of Neurons:

Cell Body (Soma): Contains the nucleus and other organelles; responsible for metabolic activities of the neuron.

Dendrites: Tree-like branches that receive electrical signals from other neurons.

Axon: The long extension that transmits electrical impulses away from the cell body to other neurons or muscles.

Axon Terminals: Release neurotransmitters to communicate with other neurons or effector cells.

Myelin Sheath: Fatty layer surrounding the axon (formed by oligodendrocytes in the CNS and Schwann cells in the PNS), which helps speed up electrical signal conduction.

Types of Neurons:

Sensory Neurons: Transmit sensory information from receptors (e.g., skin, eyes) to the central nervous system (CNS).

Motor Neurons: Carry signals from the CNS to muscles and glands to elicit a response.

Interneurons: Located in the CNS, connecting sensory and motor neurons, playing a critical role in processing information.

2. Ion Channels and Membrane Potential

Resting Membrane Potential:

Neurons maintain a resting membrane potential of about -70mV, which is created by differences in the concentration of ions inside and outside the cell (mostly Na+, K+, and Cl- ions).

The sodium-potassium pump plays a key role in maintaining these gradients by pumping 3 Na+ out of the cell for every 2 K+ in.

Action Potential:

Depolarization: When a neuron is stimulated, sodium channels open, causing an influx of Na+ ions and a shift in membrane potential.

Repolarization: Potassium channels open, and K+ ions flow out of the neuron, restoring the resting potential.

Hyperpolarization: The membrane potential becomes more negative than the resting potential before returning to its resting state.

3. Synaptic Transmission

Chemical Synapses:

Neurons communicate across synapses via the release of neurotransmitters.

Pre-synaptic Neuron: Releases neurotransmitters into the synaptic cleft after an action potential depolarizes the axon terminal.

Post-synaptic Neuron: The receptors on the postsynaptic membrane bind neurotransmitters, leading to depolarization or hyperpolarization.

Neurotransmitters:

Excitatory Neurotransmitters: E.g., Glutamate, which promotes the firing of action potentials in the postsynaptic neuron.

Inhibitory Neurotransmitters: E.g., GABA, which inhibits action potential firing.

Synaptic Plasticity:

Long-Term Potentiation (LTP): Strengthening of synaptic connections, important for learning and memory.

Long-Term Depression (LTD): Weakening of synapses, thought to play a role in forgetting and synaptic pruning.

4. Glial Cells and Their Functions

Astrocytes: Support neurons, maintain the blood-brain barrier, regulate blood flow, and help recycle neurotransmitters like glutamate.

Oligodendrocytes and Schwann Cells:

Oligodendrocytes form myelin in the CNS.

Schwann Cells form myelin in the PNS. Both myelinate axons, speeding up signal transmission.

Microglia: The immune cells of the CNS, involved in inflammation, immune responses, and clearing cellular debris.

Ependymal Cells: Line the ventricles of the brain and produce cerebrospinal fluid (CSF), which cushions and protects the brain.

5. Signal Transduction and Second Messengers

Receptor-Mediated Signaling:

Ionotropic Receptors: Directly linked to ion channels. For example, NMDA receptors are involved in synaptic plasticity.

Metabotropic Receptors: Involved in G-protein coupled signaling pathways. For example, dopamine receptors influence intracellular pathways that affect gene expression and neural activity.

Second Messengers:

cAMP and calcium ions (Ca2+) are important intracellular messengers that amplify and transduce signals.

Phosphorylation: The activation of proteins by the addition of phosphate groups, often mediated by protein kinases, is a key part of signal transduction.

6. Synaptic Vesicle Release and Recycling

Vesicle Fusion: Neurotransmitters are packaged into synaptic vesicles and released into the synaptic cleft when an action potential depolarizes the presynaptic terminal.

Exocytosis: The process of neurotransmitter release into the synaptic cleft, triggered by Ca2+ influx.

Reuptake: Neurotransmitters are removed from the synapse either by transporters (reuptake) into presynaptic neurons or nearby glial cells, or degraded by enzymes.

7. Cellular Mechanisms of Learning and Memory

Synaptic Plasticity: Changes in synaptic strength (either potentiation or depression) are believed to be the cellular basis of learning and memory.

Calcium Signaling: Calcium ions play a critical role in both LTP and LTD and are central to modulating synaptic strength.

Gene Expression: Learning can lead to changes in gene expression that alter the structure and function of synapses, making them more efficient at transmitting signals.