The Nervous System: Neurons

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The Nervous System Neurons Neuroglial Cells

• Packet 9.1 9.4
• Text pp. 562-5

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Central vs. Peripheral NS
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General Pathway (example)
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General Pathway

• Sensory receptors at the ends of peripheral
  nerves
• Sensory neurons input to CNS
• Interneurons integration by CNS
• Motor neurons output from CNS
• Somatic controls skeletal muscle (voluntary)
• Autonomic controls cardiac muscle, smooth
  muscle, glands (involuntary)
• Effectors muscles glands at the ends of
  peripheral nerves

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Neuron Parts

• Cell body
• Dendrites
• Axon

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Neuron Types
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Myelin

• A lipid that sometimes coats axons
• White matter myelinated axons
• Gray matter cell bodies unmyelinated axons
• Produced by neuroglial cells
• Increases efficiency of impulse transmission
  (will discuss more later)
• Multiple sclerosis

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PNS Neuroglial Cells

• Schwann cells
• Wrap around axon, forming myelin sheath
• Neurilemma outer layer containing the
  cytoplasm organelles
• Nodes of Ranvier gaps in the sheath

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CNS Neuroglial Cells

• Microglial cells
• Phagocytosis
• Oligodendrocytes
• Insulating myelin sheath around axons
• No neurilemma
• Astrocytes
• Connect to capillaries
• Form scar tissue
• Ependymal cells
• Form an epithelia-like membrane

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Damage to Nerves

• Neurons dont divide, but neuroglial cells can
  divide!
• Injury to cell body kills the neuron
• Injury to the axon
• In PNS
• Axons may regenerate Schwann cells help
• In CNS
• Axons do not regenerate no Schwann cells
• Neural stem cells in the brain