Introduction to CNS.docx

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Western University
Anatomy and Cell Biology
Anatomy and Cell Biology 3319
Kem Rogers

Introduction to CNS • Functions of the nervous system o Sensory input (afferent)  Sight, smell, taste, touch, pain, temperature etc. o Integration  Decision or processing of information o Motor output (efferent)  Response • Central Nervous System o Comprises of the brain & spinal cord o Integrating & command centre of the nervous system o Receives incoming sensory input, interprets these signals & dictates motor responses • Peripheral Nervous System o Nerves & ganglia (collection of neural cell bodies in a specific region) o Communication lines that link all regions of the body to the CNS • Divisions of PNS o Sensory or afferent (inward) division or Motor or efferent (outward) division  Somatic (interactions with environment)  Visceral (within your body) Neuron • Extreme longevity • Do not divide • High metabolic rate (many mitochondria) • Axodendritic: most abundant, synapse between terminal boutons & dendrites • Axosomatic: synapse that occur between axons & neuron cell bodies • Dendrites o Receptive sites (nerve cell) o Numerous dendrites on one neuron o All organelles present & chromatophillic substance • Cell body o Single nucleus & cytoplasm o Cytoplasm contains chromatophillic substance (large clusters of RER & free ribosomes) o Neurofibrils are bundles of immediate filaments that run as a network between chromatophillic substances o Most are located in CNS • Axon o Neuron has 1 axon o Impulse generators & conductors o Chromatophillic substance & protein-synthesizing organelles o Cytoskeleton is present o Length varies: long-nerve fibre o Bigger diameter = faster conduction o Axon collaterals: axon branches that extend from axon at more or less right angles o Whether an axon remains undivided or has collaterals – branches a lot at its end: terminal aborization o Branches end in knobs: terminal boutons • Axon terminal o Sends signal o Causes release of neurotransmitter from synaptic vesicles • Myelin sheath o Insulator • Nodes of Ranvier o Where conduction jumps to down axon • Synapse o Site at which neurons communicate o Most use neurotransmitter, some use electrical signals Types of Neurons • Multipolar Neuron o 99% neurons o Motor neurons, interneurons (lie between motor & sensory neurons, linked together into chains, diversity in size & patterns of processes, only in CNS) o Have more than 2 processes o Numerous dendrites & single axon o Some have no axon o Motor neurons (axon goes to innervate effector) & interneurons (make connections) • Unipolar neuron (Pseudounipolar Neurons) o Sensory neurons – found in sensory ganglia in PNS o No dendrites o Receptors  AP  down peripheral process  central process  brain & spinal cord o Carries nerve impulse away from cell body o Short, single process that merges from the cell body & divides like an inverted T into long branches o Starts out as bipolar  processes fuse together during development • Bipolar neuron o Have 2 processes that extend from opposite sides of cell body o Very rare o Occur in some special sensory organs (inner ear, olfactory epithelium & retina) o Action potential always goes through cell body & then onto central processes • Sensory Neuron o Afferent neurons o Make up the sensory division of PNS o Carry impulses toward CNS from sensory receptors in PNS
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