Lecture8 nervous system

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Lecture8 nervous system

  1. 1. Nervous system  Central nervous system  Brain  Spinal cord  Peripheral nervous system  Nerves  Ganglia  Nerve endings
  2. 2. Nervous tissue nerve cells NEURONS supporting cells GLIAL CELLS
  3. 3. Dendrites  Multiple processes  Receptor processes  Usually short  Branch profusely forming a dendritic tree  Become thinner as they subdivide into branches
  4. 4. Axons  Single processes  Effector processes  Usually long  Don’t branch profusely  Ends in terminal arborization – telodendron  Have constant diameter
  5. 5. Types of neurons  Sensory (afferent)  Motor (efferent)  Interneurons
  6. 6. Types of neurons  Bipolar neurons  Retina  Olfactory mucosa  Cochlear and vestibular ganglia  Pseudounipolar neurons  Sensory neurons  Multipolar neurons  Motor neurons  Interneurons
  7. 7. Nuclei of glial cells dendrite Axon hillock
  8. 8. Nissl bodies rough endoplasmic reticulum cisternaes and free ribosomes
  9. 9. Types of synapses Axosomatic Axodendritic Axoaxonic
  10. 10. Types of synapses  Excitatory  Inhibitory
  11. 11. Types of glial cells Central nervous system  Oligodendrocytes  Astrocytes  Ependymal cells  Microglia Peripheral nervous system  Schwann cells  Satellite cells
  12. 12. Astrocytes  Glial cells of central nervous system  2 types  Protoplasmic  Fibrous       support neurons surround neurons, blood vessels, synapses form a layer on outer surface of the brain and spinal cord control ionic and chemical environment of neurons regulate neuronal activity and metabolism joined to one another by gap junctions forming a continous network
  13. 13. Astrocytes Blood vessel
  14. 14. Microglial cells – Microglia  glial cells of central nervous system  phagocytic cells – belong to mononuclear phagocytic system  macrophages of CNS  derive from precursor cells in bone marrow  involved in inflammation processes in CNS  phagocyte dead neurons and an excess of neurons during embryogenesis
  15. 15. Ependymal cells  glial cells of CNS  cuboidal cells  line the ventricles of the brain and the central canal of the spinal cord
  16. 16. Oligodendrocytes  glial cells of CNS  have only a few small processes  myelin – forming cells in CNS
  17. 17. Cells forming the myelin sheath PNS Schwann cells CNS Oligodendrocytes
  18. 18. Schwann cell Internode Node of Ranvier
  19. 19. Peripheral nervous system Myelinated fibers Unmyelinated fibers One Shwann cell→ one axon One Schwann cell→ several axons Axon Shwann cell Shwann cell
  20. 20. Oligodendrocyte Axons
  21. 21. Central nervous system Myelinated fibers Unmyelinated fibers Oligodendrocytes Bare nerve fibers – not imbedded in glial cells
  22. 22. Peripheral nervous system  nerves  sensory nerves  motor nerves  mixed nerves  ganglia  nerve endings
  23. 23. Epineurium Perineurium Endoneurium
  24. 24. Nerve  Endoneurium – loose connective tissue  Perineurium – a few layers of flattened epithelium – like cells  Epineurium – dense irregular connective tissue containing blood vessels
  25. 25. Nucleolus Satelite cells Nucleus of nerve cell
  26. 26. Sensory ganglia  lie in dorsal roots of spinal cord, outside of CNS  contain cell bodies of sensory neurons – pseudounipolar  2 regions  central region – nerve fibers  peripheral region – cell bodies  cell bodies are covered by satellite cells  satellite cells – a kind of glial cells of PNS
  27. 27. Nervous system  Somatic nervous system – voluntary functions – control skeletal muscles  Autonomic nervous system – involuntary functions – control smooth muscle, secretion of some glands, modulation of cardiac rhythm
  28. 28. Autonomic nervous system  Sympathetic system – presynaptic neurons are located in thoracic and lumbar segments of spinal cord  Parasympathetic system – presynaptic neurons have their nuclei in medulla, midbrain, sacral portion of spinal cord
  29. 29. Nerve endings  afferent – sensory receptors  efferent
  30. 30. Sensory receptors  exteroceptors  proprioceptors  interoceptors
  31. 31. Sensory receptors  Nonencapsulated  Free nerve endings  Merkel endings  Encapsulated  Meissner corpuscle  Pacinian corpuscle  Ruffini corpuscle
  32. 32. Free nerve endings  Found in skin and corneal epithelium  Terminate in epidermis  Devoid of Schwann cells and myelin  Respond to touch, heat, cold, pain
  33. 33. Merkel ending  Nerve endings are attached to Merkel cells  Merkel cells – modified epidermal cells located in skin  Mechanoreceptors – sensitive to touch
  34. 34. Pacinian corpuscles  Encapsulated receptors  Ovoid structure resembling a hemisected onion  Nerve ending is surrounded by concentric lamellae of flattened cells  Found in hypodermis and deed fascia tissues  Respond to vibrations and deep pressure
  35. 35. Meissner’s corpuscles Encapsulated receptors Contain Schwann cells that form irregular, tortuous lamellae  Nerve fibers pass between lamellae  Found in the papillary layer of hairless skin (lips, fingers, hands, foots)  Respond to touch  
  36. 36. Proprioceptors  Muscle spindles  Golgi tendon organs
  37. 37. Degeneration and regeneration of peripheral nerve - steps 1. 2.   3. 4. 5. 6. 7. 8. Schwann cells proliferate and bridge the scar. The axon degenerate Anterograde degeneration – (refers to distal segment) – comprise the whole distal segment including axon and myelin sheath Retrograde degeneration – (refers to proximal segment) –extends for a short distance Debris is phagocyted by macrophages. The cell body undergoes chromatolysis. The muscle fiber shows a denervation atrophy. Shwann cell prolipherate within a connective tissue sleeve. The axon grows and penetrate the Schwann cell columns. Schwann cells produce myelin sheath on the regenerated axon.

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