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Chapter12 neuraltissuemarieb

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  • 1. Chapter 12: Fundamentals of theNervous System and Nervous Tissue Overview of the NS  PNS (Peripheral Nervous System)  CNS (Central Nervous System) Neurons Neuroglia Synapse Some nomenclature Developed by John Gallagher, MS, DVM
  • 2. Functional Overview of NS PNSCNS = Brain and 1. Sensory or afferent division Spinal Cord with sensory neurons. Integration, Brings sensory info from processing and PNS to CNS. coordination of Begins at receptors sensory data and motor commands 2. Motor or efferent division with motor neurons. Higher functions Brings motor commands to peripheral tissue. Ends at effector cells.
  • 3. Made up of neuronsand neuroglia
  • 4. Similar to fig 12.3
  • 5. Cellular Organization of Neural TissueTwo cell types:1. Neurons 1. “Excitable” cells2. Neuroglia (mostly not excitable)  Schwann cells  Satellite cells  Astrocytes  Oligodendrocytes  Microglial cells  Ependymal cells
  • 6. 1. Typical Neuron Structure Cell body or Soma with Perikaryon Dendrites Axon with axon hillock Synaptic terminals Fig 12.4
  • 7. Cell body = Soma
  • 8. The “signal,” or ActionPotential is carriedalong the neurilemmaFaster if axon ismyelinated
  • 9. Nerve structure•A nerve is USUALLY both sensoryand motor (axons transmit only in onedirection). •Some significant exceptions in cranial nerves•Similar to muscle terminology •Epineurium •Covers the nerve •Perineurium •Covers a fascicle •Endoneurium •Covers an axon Fig 12.16, p 333
  • 10. Synapse Site of communication between two nerve cells or nerve cell and effector cell  Presynaptic and postsynaptic neurons neuro-effector junctions, e.g., Motor End Plate Electrical vs. chemical synapses
  • 11. Chemical Synapse vs. Electrical SynapseSpace between two cellsSignal transduction via a neurotransmitter, usually AChMost common Direct physical contact between cells = gap junctions Direct signal transduction Rare, but occurs in CNS and HEART
  • 12. Chem.SynapseStructure 1. Axon terminal of presynaptic cell, with vesicles of neurotransmitter(NT) 2. Synaptic cleft 3. Dendrite or cell body of postsynaptic cell 4. Unidirectional
  • 13. Color enhancedTEMx 186,480
  • 14. Structural Neuron ClassificationAnaxonic In CNS and Sense OrgansUnipolar Also called pseudounipolar Sensory neurons See fig. 12.2
  • 15. Structural Neuron Classification cont. . .Bipolar Unmyelinated Rare, but important in special sensesMultipolar Most common All motor neurons
  • 16. Functional Neuron Classification 1) Sensory (Afferent) 1) Somatic 2) Visceral 2) Motor (Efferent) 1) Somatic 2) Visceral 3) Interneurons
  • 17. Neuron OrganizationDivergence - One neuron synapses with several, effectively"spreading the word".Convergence - Several neurons synapse with a single neuron,concentrating the input.Serial processing - step-wise, sequentialParallel processing - simultaneous processing of differentinformation
  • 18. 2. Neuroglia (glue)AKA Glial Cells10-50 X more glial cells than neuronsSupporting Cells Structural and nutritionalEnhance conduction  Schwann cells (neurolemmocytes)Ability to divide  Think about tumors (malignant glioma)  New Information: Some glial cells are excitable
  • 19. 2. Neuroglia (glue), cont’d In the CNS: In the PNS:  Astrocytes  Satellite Cells  Microglia  Schwann Cells  Ependymal Cells  Oligodendrocytes
  • 20. Astrocytes: largest & most numerous BBB, control of environment structural framework & repairs regulation of ions,and nutrients, gases
  • 21. Microglial cellsSmallestPhagocytosis  # during infection orinjuryDerived from white bloodcells
  • 22. Ependymal cellsLining of ventricles & central canalSome regions ciliatedSome specialized to produce and monitor CSF
  • 23. OligodendrocytesSmaller than astrocyteCover neurons with myelin in CNS (white matter vs. gray matter!) Myelin improves the rate of impulse conduction
  • 24. The Myelin Sheath p 357 The lipoprotein “myelin” is wrapped around and around the axon in “myelinated nerves.” Node of Ranvier = gap between neurolemmocytesIn CNS:  Called oligodendrocytesIn PNS:  Called neurolemmocytes or Schwann Cells
  • 25. Schwann Cells: AKA neurolemmocytes Surround all peripheral axons! Responsible for myelination of PNS Involved in repair mechanism after injury Wallerian Degeneration myelinated
  • 26. Schwann Cells (in the PNS) Nonmyelinated Myelinated Refer to Fig 12.7
  • 27. Demyelination Multiple sclerosis (p 365) Guillain-Barré Syndrome  Autoimmune destruction of  Autoimmune destruction of myelin sheath in the CNS myelin sheath in the PNS  Young adult women  Usually a consequence of  Usually idiopathic an infectious disease  Genetic?  Leg weakness
  • 28. Some TerminologyCollections of cell bodies – ganglion in PNS nucleus in CNSBundles of axons (or fibers) – tracts in CNS nerves in PNS“White matter” = myelinated axons, both nerves and tracts“Gray matter” = non-myelinated material, dendrites, synapses and cell bodies as well as nonmyelinated axons. In CNS – nucleus; in PNS - ganglia
  • 29. The circuit fig 12.9