Chap 11 nervous system part 1


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Chap 11 nervous system part 1

  1. 1. Anatomy & Physiology 1 <ul><li>Fundamentals of nervous system tissue </li></ul>
  2. 2. Nervous System <ul><li>The master controlling and communicating system of the body </li></ul><ul><li>Functions </li></ul><ul><ul><li>Sensory input – monitoring stimuli occurring inside and outside the body </li></ul></ul><ul><ul><li>Integration – interpretation of sensory input </li></ul></ul><ul><ul><li>Motor output – response to stimuli by activating effector organs </li></ul></ul>
  3. 3. Nervous System Figure 11.1
  4. 4. Organization of the Nervous System <ul><li>Central nervous system (CNS) </li></ul><ul><ul><li>Brain and spinal cord </li></ul></ul><ul><ul><li>Integration and command center </li></ul></ul><ul><li>Peripheral nervous system (PNS) </li></ul><ul><ul><li>Paired spinal and cranial nerves </li></ul></ul><ul><ul><li>Carries messages to and from the spinal cord and brain </li></ul></ul>
  5. 5. <ul><li>Sensory (afferent) division </li></ul><ul><ul><li>Sensory afferent fibers – carry impulses from skin, skeletal muscles, and joints to the brain </li></ul></ul><ul><ul><li>Visceral afferent fibers – transmit impulses from visceral organs to the brain </li></ul></ul><ul><li>Motor (efferent) division </li></ul><ul><ul><li>Transmits impulses from the CNS to effector organs </li></ul></ul>Peripheral Nervous System (PNS): Two Functional Divisions
  6. 6. <ul><li>Somatic nervous system </li></ul><ul><ul><li>Conscious control of skeletal muscles </li></ul></ul><ul><li>Autonomic nervous system (ANS) </li></ul><ul><ul><li>Regulates smooth muscle, cardiac muscle, and glands </li></ul></ul><ul><ul><li>Divisions – sympathetic and parasympathetic </li></ul></ul>Motor Division: Two Main Parts
  7. 7. <ul><li>The two principal cell types of the nervous system are: </li></ul><ul><ul><li>Neurons – excitable cells that transmit electrical signals </li></ul></ul><ul><ul><li>Supporting cells – cells that surround and wrap neurons </li></ul></ul>Histology of Nerve Tissue
  8. 8. <ul><li>The supporting cells (neuroglia or glial cells): </li></ul><ul><ul><li>Provide a supportive scaffolding for neurons </li></ul></ul><ul><ul><li>Segregate and insulate neurons </li></ul></ul><ul><ul><li>Guide young neurons to the proper connections </li></ul></ul><ul><ul><li>Promote health and growth </li></ul></ul>Supporting Cells: Neuroglia
  9. 9. <ul><li>Most abundant, versatile, and highly branched glial cells </li></ul><ul><li>They cling to neurons and their synaptic endings, and cover capillaries </li></ul><ul><li>Functionally, they: </li></ul><ul><ul><li>Support and brace neurons </li></ul></ul><ul><ul><li>Anchor neurons to their nutrient supplies </li></ul></ul><ul><ul><li>Guide migration of young neurons </li></ul></ul><ul><ul><li>Control the chemical environment </li></ul></ul>Astrocytes
  10. 10. Astrocytes Figure 11.3a
  11. 11. <ul><li>Microglia – small, ovoid cells with spiny processes </li></ul><ul><ul><li>Phagocytes that monitor the health of neurons </li></ul></ul><ul><li>Ependymal cells – range in shape from squamous to columnar </li></ul><ul><ul><li>They line the central cavities of the brain and spinal column </li></ul></ul>Microglia and Ependymal Cells
  12. 12. Microglia and Ependymal Cells Figure 11.3b, c
  13. 13. <ul><li>Oligodendrocytes – branched cells that wrap CNS nerve fibers </li></ul><ul><li>Schwann cells (neurolemmocytes) – surround fibers of the PNS </li></ul><ul><li>Satellite cells surround neuron cell bodies with ganglia </li></ul>Oligodendrocytes, Schwann Cells, and Satellite Cells
  14. 14. Oligodendrocytes, Schwann Cells, and Satellite Cells Figure 11.3d, e
  15. 15. <ul><li>Structural units of the nervous system </li></ul><ul><ul><li>Composed of a body, axon, and dendrites </li></ul></ul><ul><ul><li>Long-lived, amitotic, and have a high metabolic rate </li></ul></ul><ul><li>Their plasma membrane functions in: </li></ul><ul><ul><li>Electrical signaling </li></ul></ul><ul><ul><li>Cell-to-cell signaling during development </li></ul></ul>Neurons (Nerve Cells)
  16. 16. Neurons (Nerve Cells) Figure 11.4b
  17. 17. <ul><li>Contains the nucleus and a nucleolus </li></ul><ul><li>Is the major biosynthetic center </li></ul><ul><li>Is the focal point for the outgrowth of neuronal processes </li></ul><ul><li>Has no centrioles (hence its amitotic nature) </li></ul><ul><li>Has well-developed Nissl bodies (rough ER) </li></ul><ul><li>Contains an axon hillock – cone-shaped area from which axons arise </li></ul>Nerve Cell Body (Perikaryon or Soma)
  18. 18. <ul><li>Armlike extensions from the soma </li></ul><ul><li>Called tracts in the CNS and nerves in the PNS </li></ul><ul><li>There are two types: axons and dendrites </li></ul>Processes
  19. 19. <ul><li>Short, tapering, and diffusely branched processes </li></ul><ul><li>They are the receptive, or input, regions of the neuron </li></ul><ul><li>Electrical signals are conveyed as graded potentials (not action potentials) </li></ul>Dendrites of Motor Neurons
  20. 20. <ul><li>Slender processes of uniform diameter arising from the hillock </li></ul><ul><li>Long axons are called nerve fibers </li></ul><ul><li>Usually there is only one unbranched axon per neuron </li></ul><ul><li>Rare branches, if present, are called axon collaterals </li></ul><ul><li>Axonal terminal – branched terminus of an axon </li></ul>Axons: Structure
  21. 21. <ul><li>Generate and transmit action potentials </li></ul><ul><li>Secrete neurotransmitters from the axonal terminals </li></ul><ul><li>Movement along axons occurs in two ways </li></ul><ul><ul><li>Anterograde — toward axonal terminal </li></ul></ul><ul><ul><li>Retrograde — away from axonal terminal </li></ul></ul>Axons: Function
  22. 22. <ul><li>Whitish, fatty (protein-lipoid), segmented sheath around most long axons </li></ul><ul><li>It functions to: </li></ul><ul><ul><li>Protect the axon </li></ul></ul><ul><ul><li>Electrically insulate fibers from one another </li></ul></ul><ul><ul><li>Increase the speed of nerve impulse transmission </li></ul></ul>Myelin Sheath
  23. 23. <ul><li>Formed by Schwann cells in the PNS </li></ul><ul><li>A Schwann cell: </li></ul><ul><ul><li>Envelopes an axon in a trough </li></ul></ul><ul><ul><li>Encloses the axon with its plasma membrane </li></ul></ul><ul><ul><li>Has concentric layers of membrane that make up the myelin sheath </li></ul></ul><ul><li>Neurilemma – remaining nucleus and cytoplasm of a Schwann cell </li></ul>Myelin Sheath and Neurilemma: Formation
  24. 24. Myelin Sheath and Neurilemma: Formation Figure 11.5a-c
  25. 25. <ul><li>Gaps in the myelin sheath between adjacent Schwann cells </li></ul><ul><li>They are the sites where axon collaterals can emerge </li></ul>Nodes of Ranvier (Neurofibral Nodes) InterActive Physiology ® : Nervous System I: Anatomy Review PLAY
  26. 26. <ul><li>A Schwann cell surrounds nerve fibers but coiling does not take place </li></ul><ul><li>Schwann cells partially enclose 15 or more axons </li></ul>Unmyelinated Axons
  27. 27. <ul><li>Both myelinated and unmyelinated fibers are present </li></ul><ul><li>Myelin sheaths are formed by oligodendrocytes </li></ul><ul><li>Nodes of Ranvier are widely spaced </li></ul><ul><li>There is no neurilemma </li></ul>Axons of the CNS
  28. 28. <ul><li>White matter – dense collections of myelinated fibers </li></ul><ul><li>Gray matter – mostly soma and unmyelinated fibers </li></ul>Regions of the Brain and Spinal Cord
  29. 29. <ul><li>Structural: </li></ul><ul><ul><li>Multipolar — three or more processes </li></ul></ul><ul><ul><li>Bipolar — two processes (axon and dendrite) </li></ul></ul><ul><ul><li>Unipolar — single, short process </li></ul></ul>Neuron Classification
  30. 30. <ul><li>Functional: </li></ul><ul><ul><li>Sensory (afferent) — transmit impulses toward the CNS </li></ul></ul><ul><ul><li>Motor (efferent) — carry impulses away from the CNS </li></ul></ul><ul><ul><li>Interneurons (association neurons) — shuttle signals through CNS pathways </li></ul></ul>Neuron Classification
  31. 31. Comparison of Structural Classes of Neurons Table 11.1.1
  32. 32. Comparison of Structural Classes of Neurons Table 11.1.2
  33. 33. Comparison of Structural Classes of Neurons Table 11.1.3
  34. 34. <ul><li>Neurons are highly irritable </li></ul><ul><li>Action potentials, or nerve impulses, are: </li></ul><ul><ul><li>Electrical impulses carried along the length of axons </li></ul></ul><ul><ul><li>Always the same regardless of stimulus </li></ul></ul><ul><ul><li>The underlying functional feature of the nervous system </li></ul></ul>Neurophysiology
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