reflex: (1) receptors, (2) sensory neurons, (3) CNS
with one or more synapses, (4) motor neurons,
(5) effector that responds.- Stretch reflex—a muscle that is stretched will con-
tract; these reflexes help keep us upright against
gravity. The patellar reflex is also used clinically to
assess neurologic functioning, as are many other
reflexes (Fig. 8–5). - Flexor reflex—a painful stimulus will cause with-
drawal of the body part; these reflexes are protec-
tive.
The Brain—many parts that function as an
integrated whole; see Figs. 8–6 and 8–8 for
locations
- Ventricles—four cavities: two lateral, 3rd, 4th; each
contains a choroid plexus that forms cerebrospinal
fluid (Figs. 8–6 and 8–7). - Medulla—regulates the vital functions of heart
rate, breathing, and blood pressure; regulates
reflexes of coughing, sneezing, swallowing, and
vomiting. - Pons—contains respiratory centers that work with
those in the medulla. - Midbrain—contains centers for visual reflexes,
auditory reflexes, and righting (equilibrium)
reflexes. - Cerebellum—regulates coordination of voluntary
movement, muscle tone, stopping movements, and
equilibrium; contributes to sensations involving
texture and weight. - Hypothalamus—produces antidiuretic hormone
(ADH), which increases water reabsorption by the
kidneys; produces oxytocin, which promotes uter-
ine contractions for labor and delivery; produces
releasing hormones that regulate the secretions of
the anterior pituitary gland; regulates body tem-
perature; regulates food intake; integrates the func-
tioning of the autonomic nervous system (ANS);
promotes visceral responses to emotional situa-
tions; acts as a biological clock that regulates body
rhythms. - Thalamus—groups sensory impulses as to body
part before relaying them to the cerebrum; aware-
ness of pain but inability to localize; suppresses
unimportant sensations to permit concentration;
contributes to alertness and awareness, and to
memory. - Cerebrum—two hemispheres connected by the
corpus callosum, which permits communication
between the hemispheres. The cerebral cortex is
the surface gray matter, which consists of cell bod-
ies of neurons and is folded extensively into convo-
lutions. The internal white matter consists of nerve
tracts that connect the lobes of the cerebrum to one
another and to other parts of the brain.- Frontal lobes—motor areas initiate voluntary
movement; premotor area regulates sequences of
movements for learned skills; prefrontal area for
aspects of social behavior; Broca’s motor speech
area (left hemisphere) regulates the movements
involved in speech. - Parietal lobes—general sensory area feels and
interprets the cutaneous senses and conscious
muscle sense; taste area extends into temporal
lobe, for sense of taste; speech areas (left hemi-
sphere) for thought before speech. - Temporal lobes—auditory areas for hearing and
interpretation; olfactory areas for sense of smell
and interpretation; speech areas for thought
before speech. - Occipital lobes—visual areas for vision; interpre-
tation areas for spatial relationships. - Association areas—in all lobes, for abstract
thinking, reasoning, learning, memory, and
personality. The hippocampi are essential for
the formation of memories. Neural plasticity is
the ability of the brain to adapt to changing
needs. - Basal ganglia—gray matter within the cerebral
hemispheres; regulate accessory movements and
muscle tone.
Meninges and Cerebrospinal Fluid (CSF) (see
Figs. 8–9 and 8–10)- Three meningeal layers made of connective tissue:
outer—dura mater; middle—arachnoid membrane;
inner—pia mater; all three enclose the brain and
spinal cord. - Subarachnoid space contains CSF, the tissue fluid
of the CNS. - CSF is formed continuously in the ventricles
of the brain by choroid plexuses, from blood
plasma. - CSF circulates from the ventricles to the central
canal of the spinal cord and to the cranial and
spinal subarachnoid spaces. - CSF is reabsorbed from the cranial subarachnoid
space through arachnoid villi into the blood in the
cranial venous sinuses. The rate of reabsorption
equals the rate of production.
The Nervous System 193