Regulation and Integration of the Body
As we noted, the hypothalamus is the main integration center of
the autonomic nervous system. In general, anterior hypothalamic
regions direct parasympathetic functions, and posterior areas di-
rect sympathetic functions. Hypothalamic centers exert their ef-
fects both directly and via relays through the
which in turn inﬂuences the preganglionic motor neurons in the
brain stem and spinal cord (Figure 14.8). Te hypothalamus, act-
ing through the ANS, coordinates heart activity, blood pressure,
body temperature, water balance, and endocrine activity.
Te hypothalamus also mediates our reactions to fear via
its associations with the amygdala and the periaqueductal gray
matter. Emotional responses of the limbic system of the cere-
brum to danger and stress signal the hypothalamus to activate
the sympathetic system to ﬁght-or-ﬂight status. In this way, the
hypothalamus serves as the keystone of the emotional and vis-
ceral brain. Trough its centers, emotions inﬂuence ANS func-
tion and behavior.
Originally, scientists believed the ANS was not subject to vol-
untary controls. However, we have all had occasions when just
remembering a frightening event made our heart race (sympa-
thetic response) or the thought of a favorite food, pecan pie for
example, made our mouth water (parasympathetic response).
Tese inputs converge on the hypothalamus through its con-
nections to the limbic lobe.
Additionally, studies have shown that voluntary cortical con-
trol of visceral activities is possible—a capability untapped by
Inﬂuence of Biofeedback on Autonomic Function
is a way of becoming aware of physiological conditions
(such as heart rate and blood pressure), with the goal of being
able to inﬂuence them consciously. During
, subjects are connected to monitoring devices that detect
and amplify changes in these physiological processes. Te feed-
back comes in the form of ﬂashing lights or audible tones.
Subjects try to alter or control some “involuntary” function
by concentrating on calming, pleasant thoughts. Te monitor
allows them to identify changes in the desired direction, so they
can recognize the feelings associated with these changes and
learn to produce the changes at will.
Biofeedback techniques have been successful in helping indi-
viduals plagued by migraine headaches. Some cardiac patients also
use them to manage stress and reduce their risk of heart attack.
However, biofeedback training is time-consuming and o±en frus-
trating, and the training equipment is expensive and diﬃcult to use.
Check Your Understanding
Name the division of the ANS that does each of the following:
increases digestive activity; increases blood pressure; dilates
bronchioles; decreases heart rate; stimulates the adrenal
medulla to release its hormones; causes ejaculation.
Would you ﬁnd nicotinic receptors on skeletal muscle?
Smooth muscle? Eccrine sweat glands? The adrenal medulla?
Control of Autonomic Function
Although the ANS is not usually considered to be under vol-
untary control, its activity is regulated by CNS controls in the
spinal cord, brain stem, hypothalamus, and cerebral cortex
. In general, the hypothalamus is the integrative
center at the top of the ANS control hierarchy. From there,
orders ﬂow to lower and lower CNS centers for execution.
Although the cerebral cortex may modify the workings of the
ANS, it does so at the subconscious level and by acting through
limbic system structures on hypothalamic centers.
Brain Stem and Spinal Cord Controls
Te hypothalamus is the “boss,” but the brain stem reticular for-
mation appears to exert the most
inﬂuence over autonomic
functions (see Figure 12.14 on p. 446). For example, certain mo-
tor centers in the ventrolateral medulla (
) reﬂexively regulate heart rate and blood vessel diameter. Other
medullary regions oversee gastrointestinal activities. Most sensory
impulses involved in these autonomic reﬂexes reach the brain stem
via vagus nerve aﬀerents. Midbrain centers (
trol the muscles concerned with pupil diameter and lens focus.
Defecation and micturition (urination) reﬂexes that empty
the rectum and urinary bladder are integrated at the spinal cord
level but are subject to conscious inhibition. We will describe all
of these autonomic reﬂexes in later chapters in relation to the
organ systems they serve.
The “boss”: Overall
integration of ANS
Reflexes for urination,
(reticular formation, etc.)
Regulates pupil size, heart,
blood pressure, airflow,
Levels of ANS control.
The hypothalamus stands at the
top of the control hierarchy as the integrator of ANS activity, but it is in-
ﬂuenced by subconscious cerebral inputs via limbic system connections.