CBNS 106 Lec. 2 (Neurons and Glia) PDF

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CBNS 106 Lec. 2 (Neurons and Glia)...

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Neurons and Glia Two Major Classes of Cells in the Brain 1. Neurons - Neuron function is to receive, integrate and transmit information - There are ~ 85 billion neurons in the human brain - Each neuron receives on average > 1,000 synaptic inputs 2. Glia - The term glia means glue - There are three major types of glia: a. Oligodendrocytes & Schwann cells wrap around the axon to provide insulation in the form of myelin. Oligodendrocytes are found in the central nervous system (CNS) and Schwann cells are found in the peripheral nervous system (PNS) b. Astrocytes provide supporting functions for neurons. They buffer potassium ions, take up glutamate released by neurons, and provide metabolic fuel. c. Microglia are the resident immune cells of the brain. They become activated to help fight off infection and clear cellular debris via phagocytosis (the ingestion of bacteria)

Glia and Neurons Properties - Glia insulate, support, and nourish neurons - Neurons - Excitable cells - Process information - Sense environmental changes - Communicate changes to other neurons - Command body response Evolution of Cellular Neuroscience - Histology - Microscopic study of tissue structure - Nissl stain: Stains cell bodies - Facilitates the study of cytoarchitecture in the CNS - Stains the nucleus of cells (individual spots within the tissue that are individual cells) - Golgi stain: Sparsely stains whole cells - Allows imaging of a whole neuron (cell body and neurites)

The Golgi Stain - Developed by Camillo Golgi (italian) - Using silver nitrate to densely stain an entire single neuron including its dendrite and axon branches - Revealed two parts of neurons: - Soma and perikaryon (the cell body of a neuron, containing the nucleus) - Neurites: axons and dendrites - Described nervous system as a continuous network - The Reticular Theory: was debunked; everything in the nervous system, such as brain, is a single continuous network - Ramon y Cajal’s Contribution (spanish) - Use of Golgi stain to illustrate: - Neuron doctrine: nervous system is made up of discrete individual cells - Neurons communicate by contact, not continuity. -> - Debunked that neurons were not fused with other neurons that were nearby - The axon (colored yellow) is in contact with a dendrite (colored blue). - Neural circuitry - Communicate via chemical synaptic transmission - Culminating in the sharing of the 1906 Nobel Prize – Cajal and Golgi - Drew: Hippocampal Circuitry 1911 and Cerebellum Purkinje and Granular Neurons 1899 -> Neuron Diversity is Reflected in Their Morphology

Advances in neuroimaging and data processing to understand neural circuitry - Transmission Electron Microscope & Images Neuron - A simplified or “model” neuron: The Pyramidal Neuron -> - Parts of the Neuron 1. Soma: Cell Body 2. Nucleus: Inside Cell Body 3. Dendrites 4. Axon Hillock: generates impulse 5. Axon 6. Myelin (optional): Glia cell types that wrap around the axon 7. Node of Ranvier: Gaps between myelin sheaths 8. Axon Collateral: side branch extending from the axon 9. Presynaptic Terminal: a specialized area within the axon of the presynaptic cell that contains neurotransmitters enclosed in synaptic vesicles 10. Synaptic Vesicles: store various neurotransmitters that are released at the synapse 11. Synaptic Cleft: The space between the presynaptic and postsynaptic membranes (gap between 2 neurons) 12. Postsynaptic Density: a network of proteins within and adjacent to the postsynaptic membrane, consisting of anchoring and scaffolding molecules, signaling enzymes and cytoskeletal components that spatially and functionally organize the neurotransmitter receptors at the synapse.

Components of The Prototypical Neuron -

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The Neuronal Membrane - Phospholipid membrane barrier that encloses cytoplasm - ~5 nm thick - Protein concentration in the membrane varies. - Structure of discrete membrane regions influences neuronal function Cytoplasm: contents within a cell membrane (e.g., cytosol, organelles, excluding the nucleus) - Cytosol: watery fluid inside the cell - Hydrophilic heads (water-loving) inside the cell; polar head containing phosphate - Hydrophobic tails (hate water) in phospholipid bilayer; non-polar tails containing hydrocarbon - Organelles: membrane enclosed structures within the soma The Nucleus - Gene expression - Transcription - RNA processing

changes genetic expression depending on what exons are incorporated

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Ribosomes the major site for protein synthesis - Rough Endoplasmic Reticulum: Proteins synthesized here are destined to be inserted into the membrane - Protein synthesis also on free ribosomes (not bound to ER); Polyribosomes (several free ribosomes attached by a “thread”; The thread is a single strand of mRNA, and the associated ribosomes are working on it to make multiple copies of the same protein) - Free ribosomes produce cytosolic proteins (proteins that are released into the cytosol and used within the cell)...