Page 308 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

10 Neuromuscular and Sensory Systems F. Lang

Overview
The nervous system receives stimuli from the which may be localized (e.g., individual mus-
surroundings and its own body, and also di- cles) or generalized (e.g., the entire muscula-
rects the body’s functions by influencing mus- ture). Such damage can result in overactivity
cle activity and autonomic nervous functions (e.g., involuntary muscle cramps or inadequate
(e.g., vascular tone, sweat secretion). activity of sensory receptors with faulty sen-
The sensory signals influence motor and au- sory perceptions), or functional deficits (mus-
tonomic nervous functions in manifold ways cle paralysis or sensory deficits). Even when
by means of reflexes and complex connections. the sensory receptors are intact, sensory per-
A few of the signals first reach the primary ception, especially via the eyes and ears, may
sensory cortex via the thalamus and there be- be impaired if the transmission apparatus is
come conscious. These perceived signals are defective.
then analyzed, interpreted, evaluated (devel- An interruption of peripheral nerve conduc-
opment of emotions), and in certain circum- tion (→ A2) impairs the signals that are propa-
stances stored (memory) by secondary sen- gated in this nerve, but different types of fibers
sory cortical areas. (e.g., myelinated and nonmyelinated) may be
The emotions, which arise from current per- affected differently. The result of complete dis-
ceptions or items of memory, can bring about ruption of nerve conduction is flaccid paraly-
motor activity. It is the task of associated corti- sis, loss of sensation and of autonomic regula-
cal areas to plan sensible motor responses. The tion in the innervation area of the affected
motoneurons that stimulate the muscle fibers nerve. Analogously, lesions of a spinal nerve
are ultimately activated via basal ganglia, cere- affect the corresponding dermatome. Diagno-
bellum, thalamus, and the primary motor cor- sis of nerve lesions thus requires an exact
tex. knowledge of the innervation area of individ-
The sensory, motor, and autonomic nervous ual nerves and dermatomes (cf. anatomy text-
systems are closely interconnected at every books).
level, and thus the autonomic nervous system Lesions of the spinal cord (→ A3) can cause
is also under the influence of sensory and mo- loss of sensory perception and/or autonomic
tor activity and of the emotions. functions as well as flaccid or spastic paralysis.
Disorders of the nervous system can have Conversely, abnormal stimulation of neurons
many different causes, such as genetic defects, can lead to inadequate sensations and func-
degenerative diseases, tumors, mechanical le- tions. The affected areas approximately follow
sions (trauma), bleeding, ischemia, systemic the distribution of the dermatomes.
metabolic disorders (hypoglycemia, hypergly- Lesions in supraspinal structures (→ A4)
cemia, uremia, liver failure, endocrine disor- can also result in deficits or abnormal excita-
ders, etc.), and electrolyte abnormalities. tions that are circumscribed both as to func-
Other possible causes include drugs, toxins tion and to body region (e.g., in localized le-
(e.g., heavy metals, alcohol), radiation, inflam- sions in primary sensory cortical areas). How-
mation, and infection (viruses, bacteria, ever, more commonly they cause complex dis-
prions, autoimmune diseases). orders of the sensory and motor systems and/
The functions of the effectors in the periph- or autonomic regulation. Additionally, impair-
ery (sensory receptors, muscles, and organs in- ment of integrative cerebral functions such as
nervated by the autonomic nervous system; memory, emotions, or cognition may occur in
→ A1), peripheral nerve conduction (→ A2), the course of a variety of diseases.
spinal cord function (→ A3), and/or the su-
praspinal nervous system (→ A4) can be im-
paired as a consequence of nervous system
disorders.
298 Damage to the peripheral effectors (→ A1)
leads to disturbance of the particular function,
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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