Question: 100% NCERT covered from Particular Keyword.Explanations are 100% from NCERT | [Difficult level: Easy] From NCERT NEET 2020
Match the following columns and select the correct option
Column - I Column - II
(a) The organ of Corti (i) Connects the middle ear and pharynx
(b) Cochlea (ii) Coiled part of the labyrinth
(c) Eustachian tube (iii) Attached to the oval window
(d) Stapes (iv)Located on the basilar membrane
(a) (b) (c) (d)
1. (iii) (i) (iv) (ii)
2. (iv) (ii) (i) (iii)
3. (i) (ii) (iv) (iii)
4. (ii) (iii) (i) (iv)
Ans:2. (iv) (ii) (i) (iii)
👉ALFONSO CORTI, Italian anatomist, was born in 1822. Corti began
his scientific career studying the cardiovascular systems of
reptiles. Later, he turned his attention to the mammalian
auditory system. In 1851, he published a paper describing a
structure located on the basilar membrane of the cochlea
containing hair cells that convert sound vibrations into nerve
impulses, the organ of Corti. He died in the year 1888.
👉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 (Figure 21.7). 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 (the ear drum).
There are very fine hairs and
wax-secreting 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.
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.
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 (Figure 21.8). 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 (macula is the
sensory part of 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
How does ear convert sound waves into neural impulses, which are
sensed and processed by the brain enabling us to recognise a sound ?
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 ear can be divided into the outer ear, the middle ear and the inner ear. The
middle ear contains three ossicles called malleus, incus and stapes. The fluid
filled inner ear is called the labyrinth, and the coiled portion of the labyrinth is
called cochlea. The organ of corti is a structure which contains hair cells that act
as auditory receptors and is located on the basilar membrane. The vibrations
produced in the ear drum are transmitted through the ear ossicles and oval window
to the fluid-filled inner ear. Nerve impulses are generated and transmitted by the
afferent fibres to the auditory cortex of the brain. The inner ear also contains a
complex system located above the cochlea called vestibular apparatus. It is
influenced by gravity and movements, and helps us in maintaining balance of the
body and posture.
👉Write short notes on the following:
(a) Neural coordination (b) Forebrain (c) Midbrain
(d) Hindbrain (e) Retina (f) Ear ossicles
(g) Cochlea (h) Organ of Corti (i) Synapse