Nervous System Cells

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Nervous System Cells
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The Nervous System

• The Nervous system is responsible for
  communication
• Composed of the
• Brain
• Spinal Cord
• Nerves

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Organization of the Nervous System

• Central Nervous System (CNS)
• Brain
• Spinal Cord
• Peripheral Nervous System (PNS)
• Cranial Nerves
• Spinal Nerves

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Afferent and Efferent Divisions

• Afferent Division consists of all of the
  incoming sensory pathways
• Efferent Division Consists of all of the
  outgoing motor pathways

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Somatic and Autonomic Divisions

• Somatic Nervous System (SNS)
• Somatic Motor Division carries information to
  the somatic effectors (skeletal muscles)
• Somatic Sensory Division carries feedback
  information to somatic integration centers in the
  CNS

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Autonomic Nervous System (ANS)

• Efferent division of the ANS carries info to the
  autonomic or visceral effectors (smooth and
  cardiac muscle)
• Sympathetic division fight-or-flight response
• Parasympathetic division rest-and-repair
  division
• Visceral Sensory division carries feedback info
  to autonomic integrating centers of the CNS

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Cells of the Nervous System

• Neurons excitable cells that conduct the
  impulses that make possible all nervous system
  functions
• Glia (glial cells) support the function of
  neurons in various ways

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Glia (Neuroglia)

• 900 billion in the human nervous system
• Retain their capacity for division (makes them
  susceptible to cancer)

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Astrocytes

• Found only in the CNS
• Largest and most numerous
• Feed the neurons
• Blood-brain barrier

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Microglia

• Small, stationary cells found in the CNS
• In inflamed tissue they enlarge and move about in
  order to carry out phagocytosis of microorganisms
  and cellular debris

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Ependymal Cells

• Resemble epithelial cells
• Form thin sheets that line the fluid cavities of
  the brain
• Some secrete the fluid
• Cilia to circulate fluid

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Oligodendrocytes

• Cell with few branches
• Help hold nerve fibers together
• Produce the fatty myelin sheath around nerve
  fibers in the CNS

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Schwann Cells

• Found only in the PNS
• Functional equivalent of oligodendrocytes
• Wrap around nerve fiber

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Nodes of Ranvier

• Short space in the myelin sheath between adjacent
  Schwann cells

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Multiple Sclerosis
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Neurons

• The human brain contains about 100 billion
  neurons
• All neruons consist of a cell body and at least
  two processesan axon and a dendrite

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Neuron Structure
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Structural Classification of Neurons

• Multipolar have only one axon but several
  dendrites
• Bipolar have only one axon and only one highly
  branched dendrite
• Unipolar have only a single process extending
  from the cell body

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Structural Classification
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Functional Classification

• Neurons can be classified according to the
  direction in which they conduct impulses
• Afferent neurons transmit to the spinal cord or
  brain
• Efferent neurons transmit away from the brain
  or spinal cord
• Interneurons conduct impulses toward motor
  neurons (entirely within the CNS)

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Reflex Arc
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Nerves and Tracts

• Nerves are bundles of peripheral nerve fibers
  held together by several layers of connective
  tissue
• Endoneurium surrounds each nerve fiber
• Perineurium surrounds each fascicle
• Epineurium surround the nerve
• In the CNS bundles of nerve fibers are called
  tracts

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Nerve Structure
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