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Sense Organ - Ear
2013-02-25, 8:42 PM


                It is a small part of complex organ situated in the skull behind the eyes. A pair of well developed ears is present in all mammals.

Ear is the small part of the hearing organ which is present externally and rest of the parts located inside the head/skull. The main functions of the ear are

              ü  Hearing.

              ü  Maintenance of equilibrium: balancing, controlling.


Ø  Structure

The ear is divided into three regions. They are:

ü  External ear

ü  Middle ear

ü  Internal ear

·         External ear or Ear pinna

o   It is the visible part of the ear made up of cartilage covered by the skin.

o   Movable pinna is present composing of fibre, elastic cartilage which is deeply grooved and ridged to receive the sound vibrations from all the directions.

o   A narrow a tube is present known as auditory meatus connects to the ear (present between pinna and ear drum).

o   At the end of the narrow tube a delicate membrane is present known as ear drum / tympanum/ tympanic membrane.

o   It is a narrow tube containing hairs and glands (ceruminous secretes cerumin) helps to removes the dust particles entering into the ear.

          §  Ear drum: it is oval in shape which separates the external ear from the middle ear, it is delicate and essential to hear.


·         Middle ear

It is irregular in shape which is made up of three tiny bones known as ossicles as follows

o   Malleus/hammer: It is attached to the ear drum and look like a hammer shape consisting of head, neck and handle.

o   Incus/Anvil: It is the middle bone looks like an anvil shape present in the cavity of malleus.

o   Stapes/Stirrup – It is connected to the internal ear looks like a stirrup shape consisting of head, neck, two limbs and base.

Working process of Middle ear

·         It is separated from the internal ear by a bony septum known as fenestra rotundus or round membrane.

·         The stapes fix into one more membrane known as fenestra  ovalis or oval membrane.

·         This is connected to the cavities of the mouth by a narrow tube called as eustachain canal which helps in maintaining equal pressure on both sides of the tympanum.


·         Internal ear

               It is the actual part of the ear which involves in hearing consisting two cavities as follows:

o   Outer bony labyrinth: It is the outer cavity located in the bone of skull filled with the fluid Perilymph.

o   Inner membranous labyrinth: It is the inner cavity surrounded by membrane filled with a fluid Endolymph.

·         Membranous labyrinth: It is divided into three parts namely

ü  Vestibule

ü  Semi circular canals

ü  Cochlea

In this, vestibule and semi circular canals maintain the balance of the ear and cochlea is for hearing.

·         Semicircular canals and Vestibule

o   They have no auditory functions but useful for balancing.

o   The base of these canals contains swellings known as ampulla which opens into utricle and connects to sacculus.

o   The sacculus gives rise to coiled structure known as cochlea.


·         Structure of Cochlea

o   It is the spiral, coiled structure divided into three chambers as scala vestibule, scale media and scala tympanum.

o   Scala media is filled with a fluid known as Endolymph and has a special sensory cells forming organ of corti which is useful for hearing.


Ø  Working process of the ear to the brain by auditory nerve

                      ·         The sound waves which are coming from the environment enter to the tympanic membrane to   the   external ear.

                        ·         These waves transmit to the endolymph by the ossicles.

                        ·          These ossicles create the vibrations in the endolymph of the inner ear.

                       ·         Then these vibrations receive by the cochlea through organ of corti to the brain with the help of auditory nerve.

Category: My files | Added by: anve
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