CNS Neuroglial Cells

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CNS Neuroglial Cells

• Greatly outnumber neurons in the CNS (think
  worker ants vs. Queen ant)
• Microglial cells
• Scattered throughout CNS
• Support neurons and phagocytize bacterial cells
  and cellular debris
• Oligodendrocytes
• Occur in rows along nerve fibers
• Provide layers of myelin around axons within
  brain and spinal cord

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CNS Neuroglial Cells, continued.

• Astrocytes
• Found between neurons and blood vessels
• Provide structural support, help regulate
  nutrients and ions in tissues
• Form scar tissue to fill spaces after CNS
  injuries
• Ependymal cells
• Form epithelial-like membrane in parts of the
  brain (choroid plexuses)
• Form inner linings that enclose ventricles in the
  brain and central canal in the spinal cord

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CNS Neuroglial Cells
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PNS Neuroglial cells

1. Schwann cells form myelin sheath around axons

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Neurons

• Vary in size and structure, but have common
  features
• Cell Body
• Dendrites
• Axon
• Mature neurons do not divide, but neural stem
  cells can divide and form neurons or neuroglial
  cells.

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1. Cell Body

• Contains normal cellular structures (golgi
  apparatus, mitochondria, cytoplasm, cell
  membrane, etc.)
• Neurofibrils fine threads that extend into the
  axon
• Nissl bodies (chromatophilic substances)
• Membranous sacs in the cytoplasm
• Similar to rough ER
• Ribosomes on Nissl bodies synthesize ______

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2. Dendrites

• Usually short and highly branched (dendr ?)
• The main receptive surfaces for receiving
  communication from axons of other neurons

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3. Axons

• Arise from a slight elevation of the cell body,
  called the axonal hillock.
• Conduct nerve impulses away from the cell body
• Contains many mitochondria, microtubules, and
  neurofibrils
• Originates as a single structure, but may have
  branches, especially at the end to interact with
  receptive surfaces of other cells

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PNS Axons

• Enclosed in myelin sheaths composed of many
  Schwann cells
• Myelin is a lipoprotein.
• Neurilemma sheath surrounds the myelin sheath
• Nodes of Ranvier narrow gaps in the myelin
  sheath between the Schwann cells

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Classification of Neurons

• Classification based on Structural differences
• Bipolar neurons
• Unipolar neurons
• Multipolar neurons
• Classification based on Functional differences
• Sensory neurons (afferent neurons)
• Interneurons (association or internuncial
  neurons)
• Motor neurons (efferent neurons)

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Structural Differences

• Sketch the neurons below. Notes on the next 3
  slides

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Structural Differences, cont..

• Bipolar
• 2 processes
• Axon
• Dendrite
• Found in specialized parts of the eyes, nose, and
  ears

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Structural Differences, cont..

• Unipolar
• 1 process divides into 2 branches, which function
  as a single axon
• 1 branch (peripheral process) associated with
  dendrites
• Other branch (central process) enters brain or
  spinal cord

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Structural Differences, cont..

• Multipolar
• Many processes arising from cell body
• 1 axon
• Many dendrites
• Most neurons whose cell bodies lie in the brain
  or spinal cord are multipolar.
• Direction of impulse is ALWAYS from dendrites to
  axon.

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Functional Differences

• Sensory (afferent) neurons
• From peripheral body parts to the brain or spinal
  cord
• Have specialized receptor ends at the tips of
  their dendrites OR
• Dendrites closely associated with receptor cells
  in the skin or sensory organs.
• Most are unipolar, but some are bipolar.

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Functional Differences, cont..

• Interneurons (association or internuncial
  neurons)
• Lie entirely in the brain or spinal cord
• Multipolar and link other neurons
• Transmit impulses from one part of the brain or
  spinal cord to another
• Motor (efferent) neurons
• Multipolar
• Carry nerve impulses from brain or spinal cord to
  effectors
• Stimulate muscles or glands