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Download 2. Nervous System cells
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Nervous System Cells Cells of N.S. • Neurons- excitable, conduct impulses • Glial cells- provide physical support, insulation, & nutrients for neurons; do not normally conduct info. – Can still divide in adults– most N.S. tumors start here – 900 billion glial cells in NS Glial Cells • 1. Astrocytes- star shape- largest, most numerous- only in CNS – Form sheaths around brain’s capillaries- creates blood brain barrier to feed neurons using glucose from blood – May influence growth of neurons 2. Microglia • Small, stationary, in CNS • Enlarge, move, and destroy microorganisms and debris by phagocytosis in inflamed brain tissue 3. Ependymal Cells • Resemble epithelial cells • Form thin sheets in cavities, some produce fluid, some have cilia to circulate fluid 4. Oligodendrocytes • Arranged in clusters or rows • Hold nerve fibers together • Produce fatty myelin sheath –wraps around fibers in CNS 5. Schwann Cells • Only in PNS– function same as #4–wrap around a nerve fiber • Myelin- white, fatty substance in schwann cell membrane • Gaps between them are Nodes of Ranvier – *Myelin sheath and gaps are important in proper conduction of impulses Neurons • Neuron (Nerve Cells) – Basic unit of the nervous system Neurons • Parts of a Neuron –Cell Body –Dendrite –Axon –Myelin sheath • Multiple sclerosis Neural Communication Neurons Neural Communication Neurons Neural Communication Neurons Neural Communication Neurons Neural Communication Neurons Neural Communication Neurons Neural Communication Neurons Cell Body •Nucleus of neuron Dendrites • Short, branch like “trees” • Receive stimuli from other cells and conduct impulses toward the cell body and axon • Distal ends of sensory neurons = “receptors” Axons • One axon per neuron • Carries impulse away from cell body to other cells • End = axon terminal: connects to dendrite of next neuron Myelin Sheath • Covers axon of SOME neurons: myelinated • Myelin made by Schwann Cells and Oligodendrocytes • Myelin helps speed up neural impulses • Electrical insulator • Multiple Sclerosis (MS) – Myelin loss and destruction – Nerve conduction is impaired causing weakness, loss of coordination, visual and speech impairment – No known cure 3 Structural Types of Neurons • Unipolar- one process extends from cell body that branches into 2 ends—these form an axon– always sensory neurons, carry info toward CNS 3 Structural Types of Neurons • Bipolar- one axon, one very branched dendrite- least common- in sensory organs 3 Structural Types of Neurons • Multipolar- one axon, several dendrites- most in brain and spinal cord, motor & interneurons 3 functional types of Neurons: • Sensory- (Afferent) carry impulses to CNS • Motor- (Efferent)-away from CNS • Interneurons-make up CNS centers, many connections with other neurons Add to reflex and reaction ppt? Neurons • Speed of a neuron impulse –Range from 2 to 180 MPH –Measured in milliseconds • (thousandths of a second)
