Page 328 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Abnormalities of the Sensory System
Specialized receptors (sensors) of the skin are loss of gross mechanoreceptor function, tem-
stimulated by touch (mainly Meissner bodies), perature and pain sensation (dissociated disor-
pressure or tension (mainly Ruffini bodies), vi- der of sensation). Additionally, there will be ip-
bration (mainly Pacini bodies), hair movement silateral loss of the descending motor func-
(hair follicle receptors), or temperature (cold tions (lower motoneuron paralysis; → p. 310).
Systems and heat receptors). Stretch receptors (pro- A4) stops adequate vibratory sensation and di-
An interruption in the dorsal column (→
prioceptors) in muscles (muscle spindles), ten-
minishes the ability to precisely define me-
dons (Golgi tendon organs) and joint capsules
chanical stimuli in space and time, and accu-
transmit information about motor activity,
Neuromuscular and Sensory vide information about stretching of hollow tion is also affected, which means that it is
while receptors in various internal organs pro-
rately to determine their intensity. Propriocep-
organs and concentration of certain sub-
mainly information from the muscle spindles
+
which is impaired, and thus the control of
stances (CO 2 , H , glucose, osmolarity). Pain
stimuli are perceived by nociceptors (free
muscular activity. One of the effects is ataxia.
nerve endings) in the skin, motor apparatus,
In a lesion within the dorsal tracts their topo-
graphical arrangement is of importance. The
internal organs, and vessels (→ p. 320).
Sensory impulses are transmitted to the
cervical tracts lie most posterior, the sacral
A lesion in the anterolateral tract (→ A5)
motoneurons via reflexes. Via the dorsal col-
umn (fine, so-called epicritical mechanorecep-
especially impairs pressure, pain, and tem-
10 spinal cord and there influence the activity of ones medial.
tors, muscle spindle afferents, etc) and the
perature sensation. Anesthesia, hypesthesia,
anterolateral column (gross mechanorecep- hyperesthesia, paraesthesia and dysesthesia
tors, temperature, pain) they are transmitted may occur. Movements of the vertebral col-
to the medulla oblongata, thalamus, and cor- umn can, by stimulating the damaged afferent
tex (postcentral gyrus). Information about nerves, cause corresponding sensations (Lher-
movements reach the cerebellum via the spi- mitte’s sign: sudden, electric shock-like, pares-
nocerebellar tracts. The flow of information thesia in upper limbs and trunk on forward
can be interrupted at various levels. neck flexion).
Receptors that transform different stimuli Lesions in the somatosensory cortex (→ A6)
in the periphery into neuronal activity may impair the ability to separate sensations in
cease functioning or may be inadequately time and space; the sense of position and
stimulated (→ A1). This results in complete or movement have been lost, as has the ability to
partial absence of sensory perception (anes- judge the intensity of a stimulus.
thesia or hypesthesia), enhanced perception Lesions in the association tracts or cortical
(hyperesthesia), or sensory perception with- areas (→ A7) lead to abnormal processing of
out adequate stimulus (paresthesia, dysesthe- sensory perception. This results, for example,
sia). in the inability to recognize objects by feeling
Lesions in the peripheral nerves or spinal or touching them (astereognosis) and topag-
nerves can also cause anesthesia, hypesthesia, nosis (inability to identify the exact spot
hyperesthesia, paraesthesia or dysesthesia, where a sensation is felt). Abnormalities of
but also simultaneously influence propriocep- body image and position may also occur. An-
tion and motor functions (→ A2). Because of other function that may be lost is the ability
overlapping innervation areas, lesions of the to discriminate between two simultaneously
spinal nerves merely cause hypesthesia (or hy- presented stimuli (deletion phenomenon).
peresthesia) but not anesthesia of the affected Hemineglect (ignoring the contralateral half
dermatome. of the body and its environment) may also re-
Spinal cord. Hemisection of the spinal cord sult from such a lesion.
(Brown–Sequard’s syndrome; → A3), will re-
318 sult in ipsilateral loss of proprioception and of
epicritical surface sensations and contralateral
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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