Nervous System
A. Adapts to environmental influences
1. By stimulating skeletal, cardiac, and smooth muscles
2. Adaptation by the muscular system is almost
Immediate
B. Organized into different systems
1. Central nervous system (CNS)
a. Composed of the brain and spinal cord
2. Peripheral nervous system (PNS)
a. Contains the nerves to and from the body wall
that connect to the CNS
b. Also known as the somatic division because it is
under voluntary control
3. Autonomic nervous system (ANS)
a. Not under conscious control (involuntary)
b. Provides stimulus for the viscera and smooth and
cardiac muscles
c. Sympathetic division includes motor (afferent)
nerves from the ANS
d. Parasympathetic division involves motor (efferent)
nerves from the ANS
C. Nerve cell: Neuron
1. Dendrite carries impulse toward the cell body under
normal conditions
2. Axon carries impulse away from the cell body and
makes contact with the next cell; release of chemicals
starts impulse in the next neuron
3. Myelin sheath: Fatty substance around some cell axons
provides insulation
4. Neurons can carry impulses in different directionsa.
Afferent neurons carry the sensory information to
the CNS
b. Efferent neurons carry the motor information
away from the CNS
5. Central neurons are found entirely within the CNS;
relay information within the system
a. Spinal cord is approximately 45.8 cm long; occupies
the upper two thirds of the vertebral canal
b. There are 31 pairs of spinal nerves; each has a dorsal
(afferent) route and a ventral (efferent) route
D. Brain is composed of four regions
1. Cerebrum
a. Seat of conscious activities
b. Largest portion of the brain
c. Superiormost location
d. Cerebral cortex: Thin outside layer; gray color;
composed of several layers of cells; convoluted
surface
e. Longitudinal fissure: Divides cerebrum into two
hemispheres
f. Corpus callosum: Heavy band of white fibers; forms
the floor of the longitudinal fissure
g. Central fissure: Posterior to midline
h. Frontal lobe: Anterior to the central fissure
i. Parietal lobe: Posterior to the central fissure
j. Temporal lobe: Below the lateral fissure
k. Occipital lobe: Posterior part of the brain
l. Broca’s area: Controls the muscular part of speech
m. Somesthetic area: Interprets body sensations
n. Visual area: Fibers from the medial part of the retina
cross to opposite sides in the brain; fibers from
the lateral portion do not cross
o. Auditory area: Superior central portion of the temporal
lobe
p. Prefrontal area: Personality characteristics
2. Cerebellum: Coordinates balance and equilibrium
3. Medulla oblongata
a. Bulb of the spinal cord located inside the foramen
magnum
b. White on the outside, gray on the inside
c. Controls three vital functions—cardiac, respiratory,
and basal motor
d. Also controls chewing, salivation, swallowing, emesis,
lacrimation, blinking, coughing, and sneezing
e. Pons: Ropelike mass of white fibers; connects the halves of the cerebellum
4. Mesencephalon
a. Short part of the brainstem
b. Above the pons
c. Mostly white matter
E. Meninges: Membranous coverings of the brain and spinal
cord
1. Dura mater
a. Double layer around the brain
b. Single layer around the spinal cord, including the
cauda equine
2. Arachnoid
a. Membrane just inside the dura mater
b. Relatively thin
3. Pia mater
a. Soft covering that fits against the brain and spinal
cord
b. Contains an enormous amount of blood
4. Subarachnoid space
a. Threadlike structure through which cerebrospinal
fluid circulates
b. Located between the pia mater and arachnoid
F. Cranial nerves
1. Part of the PNS
2. Originate at the base of the brain
3. 12 pairs of cranial nerves
4. Referred to by name or Roman numerals
5. Provide motor impulses, sensory impulses, or mixed
impulses
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