EFFECTS OF STIMULATION OF SEMICIRCULAR CANALS
Under
experimental conditions, semicircular canals can be stimulated by two
methods:
A. Rotational movement
B. Caloric
stimulation.
ROTATIONAL MOVEMENT
Semicircular canal can be
stimulated by rotational movement with the help of Barany chair.
Barany Chair
Barany chair is a revolving
chair. The subject is seated on this chair with the head tilted forward at 30°.
Both the eyes are closed. The chair is rotated at a speed of 30 RPM for about
20 seconds and then stopped.
Effects of
Stimulation of Semicircular
Canals by Rotation
Stimulation of semicircular
canals during rotation in Barany chair produces some effects both during
rotation and after the end
of rotation.
Postrotatory
Reactions
Twenty seconds after the
stoppage of rotation in Barany chair, following reactions occur:
1. Postrotatory nystagmus: Eyes are closed
during rotation by Barany chair. When eyes are opened
after the sudden stoppage
of rotation, nystagmus starts. Postrotatory nystagmus exists for about 30
seconds.
2. Dizziness: Immediately after stoppage of rotation, there
is a feeling of unsteadiness. It is called the
dizziness. Dizziness is
associated with feeling of rotation in the opposite direction.
3. Vertigo: After the end of rotation, there is a feeling
of environment whirling around or, there is a feeling of rotation of the person
himself.
4. Other effects: Rotation for a longer period
causes nausea and vomiting. Blood pressure falls by about
10 to 15 mm Hg. And, heart
rate is reduced by 10 to 12 beats per minute.
Reaction during
Rotation with Opened Eyes
If Barany chair is rotated
with opened eyes, nystagmus occurs continuously throughout the period of
rotation.
CALORIC STIMULATION
Semicircular canals can be
stimulated bypassing hot or cold water into the ear by using a syringe. The
transmission of change in
temperature into labyrinth alters the specific gravity
of endolymph. This in turn
causes movement of cupula
and stimulation of receptor cells.
Effects of Caloric
Stimulation
Stimulation of semicircular
canals by thermal stimulus develops nystagmus, vertigo and nausea. During the treatment for ear infection, temperature of fluid instilled into the
ear must be equal to body temperature, so that, such symptoms of caloric
stimulation are avoided.
APPLIED PHYSIOLOGY – EFFECT OF
LABYRINTHECTOMY
BILATERAL
LABYRINTHECTOMY
Removal of labyrinthine
apparatus on both sides leads to complete loss of equilibrium. Equilibrium could be maintained only by visual sensation. Postural reflexes are severely affected. There is loss of
hearing sensation too.
UNILATERAL
LABYRINTHECTOMY
Removal of labyrinthine
apparatus on one side causes less effect on postural
reflexes. However, severe
autonomic symptoms occur. Autonomic
symptoms are due to unbalanced generation of impulses from the unaffected
labyrinthine apparatus. Symptoms are nausea, vomiting and diarrhea. During movement,
the symptoms become very severe. The unaffected labyrinthine apparatus starts
compensating the loss of functions of affected labyrinth. Hence, the symptoms
disappear slowly after a few months.
MOTION SICKNESS
DEFINITION
Motion
sickness is defined as the syndrome of physiological response during
movement (travel) to which
the person is not adapted.
It can occur while traveling in any form of vehicle like automobile, ship,
aircraft or spaceship. Motion sickness that occurs while traveling in a
watercraft is called seasickness.
CAUSE
Motion sickness is due to
excessive and repeated stimulation of vestibular apparatus.
Excessive and repeated stimulation of vestibular apparatus occurs because of:
1. Rapid and repeated
change in rate of motion while traveling
2. Rapid and repeated
change in direction.
Psychological factors such
as anxiety about the unfamiliar modes of travel may be added up to cause
motion sickness.
SYMPTOMS
1. Nausea
2. Vomiting
3. Sweating
4. Diarrhea
5. Pallor (paleness)
6. Excess
salivation
7. Discomfort
8. Headache
9.
Disorientation.
PREVENTION
Responses of motion
sickness can be prevented by avoiding greasy and bulky food before travel and
by
taking antiemetic drugs
(drugs preventing nausea and vomiting). In experimental animals, motion
sickness is abolished by bilateral removal of vestibular apparatus, sectioning
of vestibular nerve or ablation of flocculonodular
lobe
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