Nervous System Cells
The Nervous System
• The Nervous system is responsible for
communication
• Composed of the:
• Brain
• Spinal Cord
• Nerves
Organization of the
Nervous System
• Central Nervous System
(CNS)
• Brain
• Spinal Cord
• Peripheral Nervous
System (PNS)
• Cranial Nerves
• Spinal Nerves
Afferent and Efferent Divisions
• Afferent Division – consists
of all of the incoming
sensory pathways
• Efferent Division – Consists
of all of the outgoing motor
pathways
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
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
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
Glia (Neuroglia)
• 900 billion in the human nervous system
• Retain their capacity for division (makes
them susceptible to cancer)
Astrocytes
• Found only in the
CNS
• Largest and most
numerous
• Feed the neurons
• “Blood-brain barrier”
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
Ependymal Cells
• Resemble epithelial cells
• Form thin sheets that line
the fluid cavities of the
brain
• Some secrete the fluid
• Cilia to circulate fluid
Oligodendrocytes
• Cell with few branches
• Help hold nerve fibers
together
• Produce the fatty myelin
sheath around nerve
fibers in the CNS
Schwann Cells
• Found only in the PNS
• Functional equivalent
of oligodendrocytes
• Wrap around nerve
fiber
Nodes of Ranvier
• Short space in the
myelin sheath between
adjacent Schwann
cells
Multiple
Sclerosis
Neurons
• The human brain
contains about 100
billion neurons
• All neruons consist of
a cell body and at least
two processes–an axon
and a dendrite
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
Structural Classification
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)
Reflex Arc
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
Nerve Structure