388
UNIT 3
Regulation and Integration of the Body
11
and tightly intertwined. Although it is very complex, nervous
tissue is made up of just two principal types of cells:
Supporting cells called
neuroglia
, small cells that surround
and wrap the more delicate neurons
Neurons
, nerve cells that are excitable (responsive to stimuli)
and transmit electrical signals
See Figure 4.10 on p. 140 to refresh your memory.
Neuroglia
List the types of neuroglia and cite their functions.
Neurons associate closely with much smaller cells called
neu-
roglia
(nu-rog
9
le-ah; “nerve glue”) or
glial cells
(gle
9
al). Tere
are six types of neuroglia—four in the CNS and two in the PNS
(Figure 11.3)
. Once considered merely the “glue” or scaffolding
Central nervous system (CNS)
Brain and spinal cord
Integrative and control centers
Peripheral nervous system (PNS)
Cranial nerves and spinal nerves
Communication lines between the CNS
and the rest of the body
Parasympathetic
division
Conserves energy
Promotes house-
keeping functions
during rest
Motor (efferent) division
Motor nerve fibers
Conducts impulses from the CNS
to effectors (muscles and glands)
Sensory (afferent) division
Somatic and visceral sensory
nerve fibers
Conducts impulses from
receptors to the CNS
Somatic nervous
system
Somatic motor
(voluntary)
Conducts impulses
from the CNS to
skeletal muscles
Sympathetic division
Mobilizes body systems
during activity
Autonomic nervous
system (ANS)
Visceral motor
(involuntary)
Conducts impulses
from the CNS to
cardiac muscles,
smooth muscles,
and glands
Structure
Function
Sensory (afferent)
division of PNS
Motor (efferent)
division of PNS
Somatic sensory fiber
Visceral sensory fiber
Motor fiber of somatic nervous system
Skin
Stomach
Skeletal
muscle
Heart
Bladder
Parasympathetic motor fiber of ANS
Sympathetic motor fiber of ANS
Figure 11.2
Levels of organization in the
nervous system.
The human nervous system
is organized into two major divisions, the
central nervous system (CNS) and peripheral
nervous system (PNS). Visceral organs (primarily
located in the ventral body cavity) are served
by visceral sensory fibers and by motor fibers
of the autonomic nervous system. The somata
(limbs and body wall) are served by motor
fibers of the somatic nervous system and by
somatic sensory fibers. Arrows indicate the
direction of nerve impulses. (Connections to
spinal cord are not anatomically accurate.)
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