CELLS OF THE NERVOUS SYSTEM

• Nervous tissue is made up of 2 principal cell types:

  • Supporting cells (Neuroglia or glial cells) - support and protect neurons
  • Neurons - receive stimuli and conduct action potentials
• CNS glial cells:

  • astrocytes
  • microglia
  • ependymal cells
  • oligodendrocytes
• Astrocytes - star-shaped; most abundant and versatile neuroglia; anchors neurons to blood capilliaries
• Microglia - spiderlike phagocytes; dispose of debris and defend CNS cells
• Ependymal cell - line cavities of the brain and spinal cord; helps circulate cerebrospinal fluid (CSF)
• Oligodendrocytes - wrap around nerve fibers in the CNS; produce myelin sheaths
• Glial cells of the PNS:

  • Schwann cells
  • Satellite cells
• Schwann cells - form myelin sheath around nerve fibers in the PNS
• Satellite cells - protect and cushion neuron cell bodies
• Major regions of all neurons:

  • Cell body - nucleus and metabolic center of the cell
  • Processes - fibers that extend from the cell body
• Parts of the cell body of the neuron:

  • Nucleus with large nucleolus
  • Nissl bodies (Rough ER)
  • Neurofibrils (maintain cell shape)
• Processes (fibers) in the neuron:

  • Dendrites
  • Axons
  • Synaptic cleft
  • Synapse
• Dendrites - conduct impulses toward the cell body
• Axons - conduct impulses away from the cell body
• Synaptic cleft - gap between axon terminals and the next neuron
• Synapse - functional junction between nerves when a nerve impulse is transmitted
• Types of Neurons:

  • Multipolar neurons
  • Unipolar neurons
  • Bipolar neurons
  • Pseudo-unipolar neurons
• Multipolar neuron - many dendrites and a single axon; most common
• Unipolar neurons - sensory neurons in PNS ganglia that conduct impulses both toward and away from the cell body; located in the nose and eye
• Bipolar neurons - one dendrite and one axon
• Pseudo-unipolar neurons - have a single process extending from the cell body, which divides into 2 branches, and still function as a single axon
• Myelin - white, fatty material covering axons; speeds nerve impulse
• Neurilemma - part of Schwann cell external to the myelin sheath
• Nodes of Ranvier - gaps in myelin sheath along the axon
• Nuclei - clusters of cell bodies in the CNS

  Ganglia - collections of cell bodies in the PNS
• Tracts - bundles of nerve fibers in the CNS

  Nerves - bundles of nerve fibers in the PNS
• White matter - collections of myelinated fibers

  Gray matter - mostly unmyelinated fibers
• Myelin sheath - surrounds nerve fibers