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Figure 4.6
PNS efferent (motor) and afferent (sensory) pathways.
Autonomic Nervous System (ANS)
The ANS is connected to higher brain centers, including the medulla oblongata
and hypothalamus, which integrates the activities of the autonomic and
neuroendocrine systems.
The ANS mediates involuntary function of viscera, glands, smooth muscle,
cardiac muscle and other structures. The ANS is subdivided into the
parasympathetic nervous system (PSNS) and the sympathetic nervous system
(SNS), both of which contain afferent and efferent nerve fibers (Fig. 4.7). The
PSNS and SNS are considered to have a complementary rather than antagonistic
relationship.
PSNS
The PSNS mediates homeostatic activities (conserving and restoring energy,
control of normal heart, peristalsis, intestine and glandular activity, sphincter and
lumen dilation and constriction). Commonly referred to as the ‘rest and digest’ or
‘feed and breed’ aspect of the nervous system as it controls sexual arousal,
salivation, lacrimation, urination, digestion and defecation. The primary
neurotransmitter associated with the PSNS is acetylcholine (ACH).