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Biology for Secondary Schools

head moves, the endolymph also moves. particles of chalk known as otoliths. When
Semicircular canals are stimulated mainly the head is tilted to one side the otolith is
by rotational movement whereas the moved in the opposite direction, pulling the
utriculus responds to positional changes. sensory hairs. The sensory cells send nerve
The inner surface of utriculus and sacculus impulses to the brain which interprets them
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contain sensory cells. as a change in posture. If you spin around
for some time and then stop, you feel dizzy
The sensory hair cells have protruding hair because the fluid in your ears keeps on
embedded in jelly-like substance containing moving even after you have stopped.

Semicircular canal
Movement of head Cupula

Movement of
endolymph Ampulla
Utriculus
Movement of endolymph
Sacculus

Otoliths

Sensory hair cells Sensory nerve fibre
Figure 2.19: Positions of the semicircular canals, ampullar, utriculus and sacculus

Disorders of the ear severe cases, eardrum perforation, leading
Proper hearing depends on the efficient to long-term complications.
transmission of sound waves from the
external ear to inner ear and the response Tinnitus is a condition marked by persistent
of the sensory cells. Any interference with ringing, buzzing, or hissing sounds in
these will result into hearing disorders. the ears, often triggered by prolonged
exposure to loud noise, ear infections,
Otitis media is a common middle ear earwax accumulation, or side effects of
infection caused by bacterial or viral certain medications. This disorder can cause
infections, leading to fluid accumulation sleep disturbances, difficulty concentrating,
behind the eardrum. It often develops anxiety, and stress. Although not life-
following colds or respiratory infections. threatening, tinnitus can significantly
Symptoms include ear pain, fever, hearing affect an individual’s quality of life,
difficulties, and fluid discharge from the making management strategies essential
ear. If not treated promptly, it can result for improving daily functioning.
in chronic hearing problems, speech
development delays in children, and, in Ménière’s disease (endolymphatic
hydrops) is an inner ear disorder associated

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