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ANATOMY 215 The Nervous System: General Organization and Histology

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Queen's University
Anatomy and Cell Biology
ANAT 215
Leslie W Mac Kenzie

ANATOMY 215 The Nervous System: General Organization and Histology (Reading material: Chapter 13: pages 347-356) • Functions: • master controlling and communication system: • sensory input (somatic and visceral afferent) • integration • motor output (somatic (skeletal muscles, voluntary) and autonomic (cardiac and smooth muscles, involuntary) (sym/parasym) efferent) - dorsal and ventral roots merge into one spinal nerve as it emerges from the intervertebral foramen, then separates again into dorsal and ventral branches • Principal Subdivisions: • central nervous system (CNS): • brain and spinal cord (integration and command centre) • peripheral nervous system (PNS): • cranial nerves and spinal nerves (communications lines that link all parts of the body to the CNS) • functional subdivisions of PNS: • sensory “afferent” division: • convey impulses to the CNS • somatic afferents (from skin, skeletal muscles, joints) • visceral afferents (from organs within ventral cavity) • motor “efferent” division: • transmits impulses away from the CNS to effector organs • somatic nervous system: • somatic motor nerve fibers that conduct impulses from the CNS to skeletal muscles • voluntary nervous system • autonomic nervous system (ANS): • visceral (organs) motor fibers regulating smooth muscles, cardiac muscle, glands • involuntary nervous system Both divisions below act on the same organ with opposite effects • sympathetic division • Activate • parasympathetic division • Inhibit • Histology of the Neural Tissue: • two principal celtypes : • neurons (excitable nerve cells that transmit electrical signals) • supporting cells (smaller cells that surround and wrap the neurons) • Neurons: • called nerve cells and are the structural units of the nervous system • consists of a cell body and cytoplasmic processes • Cell Body: • also calleperikaryon or soma (interchangeably) • 5-150 um in diameter • contain usual cellular organelles except centrioles (no mitosis-can’t divide) • Nissl bodies: (a lot of them – a lot of blue(or red) stain) • rough endoplasmic reticulum • most neuron cell bodies located in CNS – more processing, less likelyto get damaged (they are protected in the CNS) ● nuclei: • clusters of nerve cell bodies in the CNS • ganglia: • fewer clusters of nerve cell bodies in PNS • Cytoplasmic Processes: • extension of the cytoplasm from the cell body • CNS contains cell bodies and processes (called track) • PNS consists mainly of neuron cell processes (called nerve) • dentrites: • short, branching extensions of the cell body (large surface area) • Receive message and convey to cell body • convey incoming messages to the cell body • axons: • one axon per neuron • comes from the axon hillock(cone shaped, void of nills bodies) of the cell body • axon collaterals: • branches along the length of the axon • functions to generate a nerve impulse and t
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