Conditions involving the nervous system often
directly involve other body systems as well. Entries
for neuromuscular disorders and neuropsychiatric
disorders in which the origins or symptoms are
primarily neurologic appear in this section, “The
Nervous System.” Entries for neuromuscular dis-
orders in which the origins or symptoms are pri-
marily muscular appear in the section “The
Musculoskeletal System.” The section “Psychiatric
Conditions and Psychological Issues” contains
entries about disturbances of mood, emotion, per-
sonality, and mental health and illness.
Structures of the Nervous SystemMENINGES second cranial nerve pair:
dura mater optic
arachnoid mater second cranial nerve pair:
pia mater oculomoter
BRAIN fourth cranial nerve pair:
cerebral cortex (cerebrum) trochlear
ventricles fifth cranial nerve pair:
amygdala trigeminal
hippocampus sixth cranial nerve pair:
thalamus abducens
HYPOTHALAMUS seventh cranial nerve pair:
corpus callosum facial
cerebellum eighth cranial nerve pair:
brainstem vestibulocochlear
pons ninth cranial nerve pair:
medulla oblongata glossopharyngeal
CRANIAL NERVES tenth cranial nerve pair:
first cranial NERVEpair: olfactory vagus
eleventh cranial nerve pair: iliohypogastric
accessory ilioinguinal
twelfth cranial nerve pair: arm
hypoglossal brachial
SPINAL CORD radial
SPINAL NERVES musculocutaneous
cervical (8 pairs, C1–C8) medial
thoracic (12 pairs, T1–T12) ulnar
lumbar (5 pairs, L1–L5) leg
sacral (5 pairs, S1–S5) femoral
coccygeal (1 pair, CO1) sciatic
PERIPHERAL NERVES common peroneal
trunk superficial peroneal
phrenic deep peroneal
intercostal tibialFunctions of the Nervous System
The nervous system regulates and directs the
functions of the body, processing billions of bio-
chemical messages—bits of information traveling
between the brain and the body—every minute. It
is the earliest system to develop in the EMBRYO.
The cells that will become the nervous system
begin to separate and distinguish themselves
about 14 days after CONCEPTION. During the follow-
ing 7 days, the neural tube, the rudiment of the
central nervous system, takes shape. By seven
weeks of gestation, the neural tube has evolved
into the SPINAL CORDand the brain. And by birth,
the nervous system is anatomically complete.
The nervous system: organization and structure
Organized into a number of structural and func-THE NERVOUS SYSTEM
The NERVOUS SYSTEMdirects the functions, voluntary and involuntary, of the body through an intricate network of spe-
cialized cells (neurons) that convey information in the form of electrochemical messages. Practitioners who diagnose
and treat conditions of the nervous system are neurologists, neurosurgeons, and neuropsychiatrists. This section, “The
Nervous System,” presents a discussion of the structure of the BRAINand nerves, an overview of neurologic functions in
health and the disorders that occur as a result of physiologic (organic) dysfunction of the brain and nerves, and entries
about the health conditions that can affect neurologic function.
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