(2) Blood vessels in the skin and mucous membranes. Constriction is
produced by alpha stimulation.
e. Salivary Glands. Thick and viscous secretions are produced by alpha
f. Stomach. The motility and tone of the stomach muscle is usually decreased
(alpha2 and beta? stimulation) and the stomach sphincters are contracted (alpha
g. Intestines. The motility and tone of the intestinal muscles are decreased
(alpha2 and beta2 stimulation) and secretions are inhibited.
h. Urinary Bladder. The wall of the bladder is usually relaxed (beta stimulation)
and the sphincter of the bladder is contracted (alpha stimulation) by stimulation from the
sympathetic nervous system.
Section IV. THE PARASYMPATHETIC NERVOUS SYSTEM
6-10. INTRODUCTION TO THE PARASYMPATHETIC NERVOUS SYSTEM
You have already been told that the parasympathetic nervous system is one
component of the autonomic nervous system. The parasympathetic nervous system
(also referred to as the cholinergic nervous system) is responsible for bringing the body
back to normal after the fight or flight response. The effects of the cholinergic nervous
system are generally the opposite of those produced by the sympathetic (adrenergic)
nervous system. The parasympathetic nervous system is responsible for maintaining
the daily functions performed within the body. This division of the autonomic nervous
system serves to conserve energy--it is necessary for life. Without the presence of this
nervous system, the absorption of necessary nutrients would be hindered,
gastrointestinal motility would be decreased, gastrointestinal secretions would be
increased, and the urinary bladder and rectum would fail to empty.
6-11. PHYSIOLOGY OF THE PARASYMPATHETIC NERVOUS SYSTEM
a. The parasympathetic nervous system is stimulated by the hypothalamus. It
has long preganglionic fibers and short postganglionic fibers (Figure 6-5). The short
postganglionic fibers are usually located within the effector organ.
b. The chemical transmitter at both the preganglionic synapse and at the
effector organ is acetylcholine. As mentioned previously, acetycholine is also the
transmitter at skeletal muscle for the somatic nervous system; however, the receptors
for the two nervous systems are different. Transmission of impulses is terminated by
the destruction of acetylcholine by the enzyme acetylcholinesterase.