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The Nervous System. Nervous Tissue: Neurons. Neurons = nerve cells….NOT NERVES! transmit messages Major regions of neurons Cell body – nucleus and metabolism Processes – fibers extending from the cell body. Neuron Anatomy. Cell body Processes of cell body

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nervous tissue neurons
Nervous Tissue: Neurons
  • Neurons = nerve cells….NOT NERVES!
    • transmit messages
    • Major regions of neurons
      • Cell body – nucleus and metabolism
      • Processes – fibers extending from the cell body
neuron anatomy
Neuron Anatomy
  • Cell body
  • Processes of cell body
    • Dendrites – conduct impulses toward the cell body (incoming)
    • Axons – conduct impulses away from the cell body (outgoing)

Figure 7.4a–b

axons and nerve impulses
Axons and Nerve Impulses
  • Axons end in axonal terminals
  • Axonal terminals contain vesicles with neurotransmitters
  • Axonal terminals are separated from the next neuron by a gap (synaptic cleft)
    • *Synapse – junction between nerves
nerve fiber coverings
Nerve Fiber Coverings
  • Schwann cells – produce myelin sheaths in jelly-roll like fashion
  • Nodes of Ranvier – gaps in myelin sheath along the axon

Figure 7.5

neuron component location
Neuron Component Location
  • Gray matter – cell bodies and unmyelinated fibers
    • Areas where signals are processed
      • Cortex of brain
      • Center of spinal cord
  • White matter – myelinated axons
    • Areas where signals are transmitted
      • Center of brain
      • Outer area of spinal cord
functional classification of neurons
Functional Classification of Neurons
  • Sensory neurons
    • Carry impulses from the sensory receptors to CNS
  • Motor neurons
    • Carry impulses from CNS
  • Interneurons
    • Connect sensory and motor neurons in the CNS
nervous tissue support cells neuroglia
Nervous Tissue: Support Cells (Neuroglia)
  • Astrocytes
    • Abundant, star-shaped cells
    • Brace neurons
    • Form barrier between capillaries and neurons
    • Control the chemical environment of the brain

Figure 7.3a

nervous tissue support cells
Nervous Tissue: Support Cells
  • Microglia
    • Spider-like phagocytes
    • Dispose of debris
  • Ependymal cells
    • Line cavities of the brain and spinal cord
    • Circulate cerebrospinal fluid

Figure 7.3b–c

nervous tissue support cells1
Nervous Tissue: Support Cells
  • Oligodendrocytes
    • Produce myelin sheath around nerve fibers in the central nervous system

Figure 7.3d

nervous tissue support cells2
Nervous Tissue: Support Cells
  • Satellite cells
    • Protect neuron cell bodies
  • Schwann cells
    • Form myelin sheath in the peripheral nervous system

Figure 7.3e

functional properties of neurons
Functional Properties of Neurons
  • Irritability – ability to respond to stimuli
  • Conductivity – ability to transmit an impulse
  • The plasma membrane at rest is polarized
    • Fewer positive ions are inside the cell than outside the cell
starting a nerve impulse
Starting a Nerve Impulse
  • Depolarization – a stimulus depolarizes the neuron’s membrane
  • A depoloarized membrane allows sodium (Na+) to flow inside the membrane
  • The exchange of ions initiates an action potential in the neuron

Figure 7.9a–c

nerve impulse propagation
Nerve Impulse Propagation
  • The impulse continues to move toward the cell body
  • Impulses travel faster when fibers have a myelin sheath

Figure 7.9d–f

the action potential
The Action Potential
  • If the action potential (nerve impulse) starts, it continues over the entire axon
  • Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane
  • The sodium-potassium pump restores the original configuration
    • This action requires ATP
continuation of the nerve impulse between neurons
Continuation of the Nerve Impulse between Neurons
  • Impulses can cross the synapse to another nerve
    • Neurotransmitter is released from the axon terminal
    • Dendrite on next neuron has receptors that are stimulated by the neurotransmitter
    • An action potential is started in the dendrite
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