Semicircular canals stimulation effects

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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