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Lecture 13 Nervous Tissues JPHubbard Bio-5

Lecture 13 Nervous Tissues JPHubbard Bio-5. Control/Communication – Two Systems Nervous Endocrine. Organization of the Nervous System. CNS is brain and spinal cord PNS is everything else. Nervous Tissue Neurons – cells responsible for conducting information 3 types

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Lecture 13 Nervous Tissues JPHubbard Bio-5

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  1. Lecture 13 Nervous TissuesJPHubbardBio-5

  2. Control/Communication – Two Systems • Nervous • Endocrine

  3. Organization of the Nervous System CNS is brain and spinal cord PNS is everything else

  4. Nervous Tissue • Neurons – cells responsible for conducting information • 3 types • Neuroglia – responsible for support of neurons • 6 types • 4 in CNS • 2 in PNS

  5. Neuron Structure Cell body Control metabolic functions/Integration Dendrites Receive information from other neurons/environment transmit towards cell body Axonal hillock – ‘trigger zone’ – develops nerve impulse Axon Conduct nerve impulse away from cell body Terminates at synaptic bulb Collaterals may form Telodendria

  6. Cell body (soma) Dendrites Axonal hillock – ‘trigger zone’ Axon Telodendria Synaptic terminal synaptic knob

  7. Parts of a Neuron Neuroglial cells Nucleus with Nucleolus Axons or Dendrites Cell body = soma

  8. Three Structural Types of Neurons • Multipolar: one axon and several dendrites • Cell bodies within CNS • Includes interneurons and motor neurons (efferent neurons) • Unipolar: one process from cell body – branches into axon and dendrite • Nuclei in ganglia outside CNS • Most sensory (afferent) neurons • Bipolar: one axon and one dendrite • Found in special sensory organs (eyes, ears, nose)

  9. Functional Classification of Neurons • Sensory: cell body outside CNS – axon extends into CNS • Interneuron: entirely within CNS • Motor: cell body in CNS (also in autonomic ganglia) – axon extends to effector

  10. Neuroglia of CNS • Astrocytes • Blood brain barrier • Control interstitial environment • Guide development, Repair, Framework of CNS • Oligodendrocytes • Form myelin covering (white matter) on one or more axons • Microglia • ‘security guards’ • Ependymal • Secretion and circul. Of cerebrospinal fluid

  11. Gray and White Matter • White matter = myelinated processes (white in color) • Gray matter = nerve cell bodies, dendrites, axon terminals, bundles of unmyelinated axons and neuroglia (gray color) • In the spinal cord = gray matter forms an H-shaped inner core surrounded by white matter • In the brain = a thin outer shell of gray matter covers the surface & is found in clusters called nuclei inside the CNS

  12. Neuroglia of PNS • Schwaan Cells • form myelin covering around single axon • May also enclose multiple unmylenated nerve fibers together • Guide and stimulate nerve fiber repair • Satellite Cells • Regulate nutrient/waste product exchange

  13. Multiple Sclerosis (MS) • Autoimmune disorder causing destruction of myelin sheaths in CNS • sheaths becomes scars or plaques • 1/2 million people in the United States • appears between ages 20 and 40 • females twice as often as males • Symptoms include muscular weakness, abnormal sensations or double vision • Remissions & relapses result in progressive, cumulative loss of function

  14. Neurons and Nerve Impulses • Excitability: ability of cell membrane to conduct electrical impulse • Neurons • Muscle fibers • Action potential: wavelike depolarization - movement of ions across axon membrane • Spreads from soma towards synaptic bulb of neurons • Trigger: development of threshold potential – sufficient stimulation • Factors affecting speed of transmission: • +/- myelin sheath • Diameter of axon

  15. Synapses: • Site of communication between neruron and another cell • Usually chemical • May involve • Two neurons • Neuron and another cell type: neuroeffector junction • One-way signal direction • Presynaptic neuron to postsynaptic neuron • Occur between synaptic bulb of presynaptic neuron and: • Dendrites/soma/axon of postsynaptic neuron

  16. Functioning of Chemical Synapses • Action potential reaches end bulb triggering release of neurotransmitter • Neurotransmitter crosses synaptic cleft • Binding of neurotransmitter alters membrane potential in postsynaptic neuron • One-way information transfer • Neurotransmitter removed • Action is transitory

  17. Neurotransmitters: • various chemical classes • Amino acids • Modified amino acids • Gasses (nitric oxide) – etc. + 50 known • Excitatory: stimulate postsynaptic neuron • Acetylcholine (loss  Alzheimer’s) • Dopamine (loss  Parkinson’s) • Serotonin (decrease assoc. with depression) • Inhibitory: inhibit signal in postsynaptic neuron • GABA

  18. Neurotransmitter Effects • Neurotransmitter effects can be modified • synthesis can be stimulated or inhibited • release can be blocked or enhanced • removal can be stimulated or blocked (agonist vs. antagonist) • Prozac = serotonin reuptake inhibitor • receptor site can be blocked or activated

  19. Terms (see table 13.1 p 332 5th ed) • Ganglion: (pl: Ganglia) Mass of cell bodies in PNS • Plexus: Network (of nerves) • Center: Group of neuron cell bodies in the CNS with common function • Nucleus: center with defined boundries • Tract: Bundle of axons within the CNS sharing common origin, destination and function • Column: A group of tracts found within a specific region of the spinal cord • Pathway: centers and tracts connecting brain with organs/systems in body

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