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Nervous Tissue
Ch. 17, p257
Nervous Tissue
• Neurons
• Neuroglia
– CNS:
•
•
•
•
Astrocytes
Oligodendrocytes
Microglia
Ependymal Cells
– PNS:
• Schwann Cells
• Satellite Cells
Neuron Anatomy
• Cell body (aka: perikaryon= cyton
=soma)
– single, central nucleus with
large
nucleolus, cell organelles
• Dendrites
– for receiving signals, conduct
impulses toward the cell body
• Axon
– for sending signals, conduct impulses
away from the cell body to effectors
– Covered by lipid myelin
Myelin
Myelin Sheath Formation
• Myelination begins
during fetal
development, but
proceeds most rapidly
in infancy.
Myelin Sheath
• Insulating layer around a nerve fiber
• 20% protein & 80 % lipid (looks white)
• In PNS, hundreds of layers wrap axon
– the outermost coil is schwann cell (neurilemma)
• In CNS, no neurilemma
• Nodes of Ranvier
– Gaps between myelin segments
• Initial segment (area before 1st schwann cell) & axon hillock
form trigger zone where signals begin
Axon Nerve Impulse Conduction Speed
Myelinated - 300MPH
Unmyleinated - 2 MPH
Neuron Classification
• Unipolar Neuron
– Single process from cell
body that is divided into
axon and dendrite
– Conduct impulses toward
CNS, sensory neurons
• Bipolar Neuron
– One dendrite and one
axon
– Occurs in retina of eye
• Multipolar Neuron
– Multiple dendrites, one
axon
– Carry impulses away from
CNS, Motor Neurons
Neuron Model
Neuron Model
Pre
Anatomy of the Brain and Cranial
Nerves
Ch. 19, pg. 279