Ear
Ear is the organ of special sense of hearing. It is also responsible forequilibrium. It is divided into three parts.
Parts of ear are
1. External Ear Lying outside the skull
2. Middle Ear Lying inside the skull
3. Internal ear
External ear : It contains two parts.They are
• Pinna - Funnelshaped organ made of fibroelastic cartilage. It is the organ of collection of sound waves .
• External auditory meatus - small channel of about 3cm length.It is lined with skin and wax creating glands are contained in this part. Hair and wax present in its outer part prevent dust particles.Its inner part is closed by a thin membrane called tympanic membrane or ear drum.This canal is the organ of
conveyance of vibrations of sound to the tympanic membrane.
Middle ear : It is a small cavity in the temporal bone,intrnal to eardrum. i.e.tympanc membrane forms its outer wall.It contains air. It contains
1. Fenestra ovalis (oval window) and fenestrarotundum (round
window).Round window is also called fenestra cochleae.
2. Eustachian tube - which communicates with nasopharynx.It helps in equalisation of pressure on both sides of tympanic membrane.
3. Auditus - Channel connecting middle ear posteriorly with mastoid antrum of temporal bone.
4. Auditory ossicles - Malleus, incus and stapes arranged across middle ear. These are minute bones of middle ear and are bound by ligaments.Theyvibrate as a single unit when sound waves impinge on tympanic membrane.
Internal ear: It contains
1. Bony labyrinth - present in petrous portion of temporal bone.
2. Membranous labyrinth - lyeing with the bony labyrinth
Fluids of Internal ear : Perilymph is the fluid of bony labyrinth. Endolymph is the fluid of membranous labyrinth. Structures of bony labyrinth :Bony labyrinth contains vestibule, cochlea and semi circular canals. Cochlea is the organ of hearing and semicircular canals for equilibrium.
Vestibule : It is present between vestibule and semicircular canals. Vestibule contains utricle and sacule. Utricle and saccule are parts of membranous labyrinth Cochlea. It is a bony spiral canal. These spirals wind rpund a central bony pillar Modiolus. Basilar membrane is membranous septum dividing cochlea into two parts. Organ of corti is the neuroepithelium of cochlea.It is auditory receptor resting on basilar membrane. Cochlear nerve fibres enter the organ of Corti. Vestibulocochlear nerve collects sensation of equilibrium from vestibular division. It col lects sensation of hearing from cochlear division. Auditory nerve fibres reach special nucleus on the back of thalamus and then cerebral cortex.
Semicircular Canals: Each ear contains three semilarcular canals. They are arranged at right angles to each other. They are superior, posterior and lateral canals. Ampulla is enlarged end of each canal. Vestibular nerve endings are present in ampullae. Ampullae help cerebellum in maintaining equilibrium. Semicircular
canals are for informing dynamic equilibrium and otolithic organ for static equilibrium.
Ear is the organ of special sense of hearing. It is also responsible forequilibrium. It is divided into three parts.
Parts of ear are
1. External Ear Lying outside the skull
2. Middle Ear Lying inside the skull
3. Internal ear
External ear : It contains two parts.They are
• Pinna - Funnelshaped organ made of fibroelastic cartilage. It is the organ of collection of sound waves .
• External auditory meatus - small channel of about 3cm length.It is lined with skin and wax creating glands are contained in this part. Hair and wax present in its outer part prevent dust particles.Its inner part is closed by a thin membrane called tympanic membrane or ear drum.This canal is the organ of
conveyance of vibrations of sound to the tympanic membrane.
Middle ear : It is a small cavity in the temporal bone,intrnal to eardrum. i.e.tympanc membrane forms its outer wall.It contains air. It contains
1. Fenestra ovalis (oval window) and fenestrarotundum (round
window).Round window is also called fenestra cochleae.
2. Eustachian tube - which communicates with nasopharynx.It helps in equalisation of pressure on both sides of tympanic membrane.
3. Auditus - Channel connecting middle ear posteriorly with mastoid antrum of temporal bone.
4. Auditory ossicles - Malleus, incus and stapes arranged across middle ear. These are minute bones of middle ear and are bound by ligaments.Theyvibrate as a single unit when sound waves impinge on tympanic membrane.
Internal ear: It contains
1. Bony labyrinth - present in petrous portion of temporal bone.
2. Membranous labyrinth - lyeing with the bony labyrinth
Fluids of Internal ear : Perilymph is the fluid of bony labyrinth. Endolymph is the fluid of membranous labyrinth. Structures of bony labyrinth :Bony labyrinth contains vestibule, cochlea and semi circular canals. Cochlea is the organ of hearing and semicircular canals for equilibrium.
Vestibule : It is present between vestibule and semicircular canals. Vestibule contains utricle and sacule. Utricle and saccule are parts of membranous labyrinth Cochlea. It is a bony spiral canal. These spirals wind rpund a central bony pillar Modiolus. Basilar membrane is membranous septum dividing cochlea into two parts. Organ of corti is the neuroepithelium of cochlea.It is auditory receptor resting on basilar membrane. Cochlear nerve fibres enter the organ of Corti. Vestibulocochlear nerve collects sensation of equilibrium from vestibular division. It col lects sensation of hearing from cochlear division. Auditory nerve fibres reach special nucleus on the back of thalamus and then cerebral cortex.
Semicircular Canals: Each ear contains three semilarcular canals. They are arranged at right angles to each other. They are superior, posterior and lateral canals. Ampulla is enlarged end of each canal. Vestibular nerve endings are present in ampullae. Ampullae help cerebellum in maintaining equilibrium. Semicircular
canals are for informing dynamic equilibrium and otolithic organ for static equilibrium.
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