Page 342 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Disorders of the Autonomic Nervous System
The sympathetic and parasympathetic ner- eration of the autonomic nerves (autonomic
vous systems are complementary regulators failure or idiopathic orthostatic hypotension).
of manifold autonomic functions. Both sys- Additionally, some drugs block sympathetic
tems can become overactive or inactive as a re- action, causing effects that are a mirror image
sult of disease of the autonomic nervous sys- of the consequences of excessive sympathetic
Systems tem. stimulation. The main effect is a drop in blood
The sympathetic nervous system can be
pressure, dysfunction of the sex organs, and ab-
normal thermoregulation due to the absence of
activated by emotions, fall in blood pressure
sweat secretion. The airway may be narrowed
(e.g., in hypovolemic shock), and hypoglyce-
Neuromuscular and Sensory adrenal medulla (pheochromocytoma) can Loss of sympathetic innervation of the eye
in those who are susceptible to this occurring.
mia. Furthermore, a tumor of the cells in the
causes Horner’s syndrome, which is character-
form and release epinephrine. Lastly, some
ized by constricted pupils (miosis) and lid
drugs can trigger sympathetic nerve activity.
When pain occurs (→ p. 320), activation of
droop (ptosis) as well as eyeball retraction (en-
ophthalmos).
sympathetic nerves may produce autonomic
side effects.
Loss of parasympathetic stimulation (e.g.,
as a result of cholinergic receptor blockers)
Activation of the sympathetic nervous sys-
thermore, bronchial, intestinal, and bladder
excitability of the heart (bathmotropism), car-
muscles, erection (in the male), vasoconges-
diac contractility (inotropism), heart rate
10 tem (→ A) will, via ß 1 -receptors, increase the leads to tachycardia and dilated pupils. Fur-
(chronotropism) as well as the conduction
tion (in the female), and tear, salivary, bron-
velocity of the action potential (dromotro- chial, and gastrointestinal secretions are in-
pism). Blood vessels in the skin, lung, kidney, hibited. If there is an anticholinergic action,
gut, and sex organs are constricted via α 1 -re- sweat secretion is also inhibited.
ceptors, while those in the heart, muscle, and Section of the spinal cord (→ C) causes the
liver are dilated by β 2 -receptors. The circula- loss of autonomic nervous system regulation.
tory effects of the sympathetic nerves are to At first, as described with respect to somato-
raise the blood pressure, the skin becomes motor functions (→ p. 310), spinal shock oc-
pale through vasoconstriction. curs. Below the level of the lesion in the spinal
The sympathetic nerves stimulate sweat cord the cutaneous blood vessels are dilated
(cholinergic) and salivary (β) secretion, hair be- and autonomic functions, for example, defeca-
comes erect (arrectores pilorum muscle [α 1 ]), tion and micturition, are lost. Normally the
eyelids are raised (levator palpebrae muscle wall tension of the bladder is measured by ten-
[α 1 ]), and the pupils dilated (dilator pupillae sion receptors (→ C). If the tension reaches a
muscle [α 1 ]). In addition, bronchial and uterine certain threshold, bladder emptying is initi-
musculature is dilated (β 2 ), the activity of the ated via a pontine “micturition center”. In
intestinal musculature is inhibited, and the spinal shock micturition ceases. If bladder
intestinal and bladder sphincters contracted. emptying is not ensured by catheterization,
Contraction of the seminal vesicle and the duc- an “overflow bladder” results, along with uri-
tus deferens triggers ejaculation. Sympathetic nary congestion and infection. However, auto-
nerves also promote muscular tremor, stimu- nomic nervous function recovers in one to six
late the breakdown of glycogen in the liver and months because new synapses are formed in
muscles (β 2 ), lipolysis (β 2 ) as well as the release the spinal cord below the lesion, and the de-
of, among others, glucagon, corticotropin, so- prived cells are sensitized. A bladder-emptying
matotropin, and renin. They also inhibit insu- reflex can be established (“automatic blad-
lin and histamine release. Finally, they aid in der”) by tapping on the abdominal wall above
mobilizating leukocytes and in aggregating the bladder. Nevertheless, supraspinal control
platelets. of bladder emptying is no longer possible.
332 Sympathetic stimulation may cease partly
or completely (a rare event) because of degen-
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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