The Ear
The ears perform two sensory functions, hearing and maintenance of body
balance. Anatomically, the ear can be divided into three major sections
called the outer ear, the middle ear and the inner ear .
Outer ear: The outer ear consists of the pinna and external auditory meatus (canal).
The pinna collects the vibrations in the air which produce sound. The
external auditory meatus leads inwards and extends up to the tympanic
membrane . There are very fine hairs and wax-secreting
sebaceous glands in the skin of the pinna and the meatus. The tympanic
membrane is composed of connective tissues covered with skin outside
and with mucus membrane inside.
Middle ear: The middle ear contains three ossicles called malleus, incus and stapes which are attached to one another in a chain-like fashion. The malleus is attached to the tympanic membrane
and the stapes is attached to the oval window of the cochlea. The ear
ossicles increase the efficiency of transmission of sound waves to the inner
ear. An Eustachian tube connects the middle ear cavity with the pharynx.
The Eustachian tube helps in equalising the pressures on either sides of
the ear drum.
Inner ear :
The fluid-filled inner ear called labyrinth consists of two parts, the
bony and the membranous labyrinths. The bony labyrinth is a series of
channels. Inside these channels lies the membranous labyrinth, which is
surrounded by a fluid called perilymph. The membranous labyrinth is
filled with a fluid called endolymph. The coiled portion of the labyrinth is
called cochlea. The membranes constituting cochlea, the reissner’s and
basilar, divide the surounding perilymph filled bony labyrinth into an
upper scala vestibuli and a lower scala tympani . The space
within cochlea called scala media is filled with endolymph. At the base of
the cochlea, the scala vestibuli ends at the oval window, while the scala
tympani terminates at the round window which opens to the middle ear.
The organ of corti is a structure located on the basilar membrane
which contains hair cells that act as auditory receptors. The hair cells
are present in rows on the internal side of the organ of corti. The basal
end of the hair cell is in close contact with the afferent nerve fibres. A large
number of processes called stereo cilia are projected from the apical part
of each hair cell. Above the rows of the hair cells is a thin elastic membrane
called tectorial membrane.
The inner ear also contains a complex system called vestibular
apparatus, located above the cochlea. The vestibular apparatus is
composed of three semi-circular canals and the otolith organ consisting
of the saccule and utricle. Each semi-circular canal lies in a different plane
at right angles to each other. The membranous canals are suspended in
the perilymph of the bony canals. The base of canals is swollen and is
called ampulla, which contains a projecting ridge called crista ampullaris
which has hair cells. The saccule and utricle contain a projecting ridge
called macula.
The crista and macula are the specific receptors of the
vestibular apparatus responsible for maintenance of balance of the body
and posture.
Mechanism of hearing :
The external ear receives sound waves and directs them to the ear drum.
The ear drum vibrates in response to the sound waves and these vibrations
are transmitted through the ear ossicles (malleus, incus and stapes) to
the oval window. The vibrations are passed through the oval window on
to the fluid of the cochlea, where they generate waves in the lymphs. The
waves in the lymphs induce a ripple in the basilar membrane. These
movements of the basilar membrane bend the hair cells, pressing them
against the tectorial membrane. As a result, nerve impulses are generated
in the associated afferent neurons. These impulses are transmitted by
the afferent fibres via auditory nerves to the auditory cortex of the brain,
where the impulses are analysed and the sound is recognised.
The ears perform two sensory functions, hearing and maintenance of body
balance. Anatomically, the ear can be divided into three major sections
called the outer ear, the middle ear and the inner ear .
Outer ear: The outer ear consists of the pinna and external auditory meatus (canal).
The pinna collects the vibrations in the air which produce sound. The
external auditory meatus leads inwards and extends up to the tympanic
membrane . There are very fine hairs and wax-secreting
sebaceous glands in the skin of the pinna and the meatus. The tympanic
membrane is composed of connective tissues covered with skin outside
and with mucus membrane inside.
Middle ear: The middle ear contains three ossicles called malleus, incus and stapes which are attached to one another in a chain-like fashion. The malleus is attached to the tympanic membrane
and the stapes is attached to the oval window of the cochlea. The ear
ossicles increase the efficiency of transmission of sound waves to the inner
ear. An Eustachian tube connects the middle ear cavity with the pharynx.
The Eustachian tube helps in equalising the pressures on either sides of
the ear drum.
Inner ear :
The fluid-filled inner ear called labyrinth consists of two parts, the
bony and the membranous labyrinths. The bony labyrinth is a series of
channels. Inside these channels lies the membranous labyrinth, which is
surrounded by a fluid called perilymph. The membranous labyrinth is
filled with a fluid called endolymph. The coiled portion of the labyrinth is
called cochlea. The membranes constituting cochlea, the reissner’s and
basilar, divide the surounding perilymph filled bony labyrinth into an
upper scala vestibuli and a lower scala tympani . The space
within cochlea called scala media is filled with endolymph. At the base of
the cochlea, the scala vestibuli ends at the oval window, while the scala
tympani terminates at the round window which opens to the middle ear.
The organ of corti is a structure located on the basilar membrane
which contains hair cells that act as auditory receptors. The hair cells
are present in rows on the internal side of the organ of corti. The basal
end of the hair cell is in close contact with the afferent nerve fibres. A large
number of processes called stereo cilia are projected from the apical part
of each hair cell. Above the rows of the hair cells is a thin elastic membrane
called tectorial membrane.
The inner ear also contains a complex system called vestibular
apparatus, located above the cochlea. The vestibular apparatus is
composed of three semi-circular canals and the otolith organ consisting
of the saccule and utricle. Each semi-circular canal lies in a different plane
at right angles to each other. The membranous canals are suspended in
the perilymph of the bony canals. The base of canals is swollen and is
called ampulla, which contains a projecting ridge called crista ampullaris
which has hair cells. The saccule and utricle contain a projecting ridge
called macula.
The crista and macula are the specific receptors of the
vestibular apparatus responsible for maintenance of balance of the body
and posture.
Mechanism of hearing :
The external ear receives sound waves and directs them to the ear drum.
The ear drum vibrates in response to the sound waves and these vibrations
are transmitted through the ear ossicles (malleus, incus and stapes) to
the oval window. The vibrations are passed through the oval window on
to the fluid of the cochlea, where they generate waves in the lymphs. The
waves in the lymphs induce a ripple in the basilar membrane. These
movements of the basilar membrane bend the hair cells, pressing them
against the tectorial membrane. As a result, nerve impulses are generated
in the associated afferent neurons. These impulses are transmitted by
the afferent fibres via auditory nerves to the auditory cortex of the brain,
where the impulses are analysed and the sound is recognised.
usefull note thankyou
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