Nerves

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Myelin
Ganglia
  • Cell types develop from neuroblasts (neural tube) and cells of neural crest
  • Neural tube is a neuroepithelium one cell thick
  • Neural tube forms CNS, neural crest forms PNS
  • Peripheral nervous system divided into two
    • Autonomic, subdivided into
      • Sympathetic
      • parasympathetic
    • Somatic
  • Neural stem cell do not persist once nervous system formed. Hence only down-regulation possible
  • Four phases of developing nerve cells
    • Neurogenesis- generation of neurons
    • Neuronal migration - spatial organisation of neuronal cell bodies within the nervous system. Primarily guided by glial cells
    • Axonogensis - axon extension towards synaptic target. Guidance by growth cones and local environment
    • Synaptogenesis - synapse formation
  • Parts of a nerve cell
    • Dendrites
    • Cell body
    • Axon
    • Synapse
  • Membrane organised into two domains : somatodendritic and axonal. Show derivation from epithelium.
  • Cytoskeleton
    • roles
      • Shape neuron
      • Maintain shape
      • Form and maintain regional specialisation though transport processes
    • structural element
      • actin microfilaments
      • tubulin microtubules
      • intermediate or neurofilaments
    • Fast axonal transport along microtubule tracks (200-400 mm/day)
      • using dynesin in retrograde direction
      • using kinesin in anterograde direction
    • Slow axonal transport at several mm/day
  • Nerve terminal
    • regions specialised for synthesis, storage, controlled release and recovery of neurotransmitters (synapses)
  • Myelin
  • Peripheral nervous system
    • Peripheral nerves are aggregations of nerve axons (myelinated and unmyelinated), glial cells (Schwann cells), blood vessels and connective tissue
    • Somatic motor nerves:
      • Have their cell bodies in the CNS in spinal cord or brainstem
      • axon run in PNS
      • efferent effector fibres
    • Somatic sensory system
      • Cell bodies located in dorsal root ganglia
      • afferent fibres convey information from peripheral sensory receptors (free nerve endings, Meissner corpuscles, Pacinian corpuscles, tendon receptors, joint receptors.
    • Autonomic nervous system
    • Peripheral nerve injury

 

6.2 TISSUES OF THE PERIPHERAL NERVOUS SYSTEM [Hist]

[Currently: 2 lectures (?) ("Autonomic n.s.") + 1 ´ 2h class]

Structure of a peripheral nerve: fascicular arrangement of axons; endoneurium, perineurium, epineurium; myelin sheaths, nodes of Ranvier.
Ganglia: organisation of dorsal root, sympathetic and enteric ganglia.
Structure and distribution of a variety of nerve endings.

 

6.5 NEURONAL DEGENERATION [Neuro]

Wallerian degeneration.
Degenerative disorders; axonal death as a cause of disease: Motor Neurone Disease.* Vincristine neuropathy as an example of a failure of the cytoskeleton.
* — Students should appreciate these two principal cellular pathologies of the central nervous system.
 

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