- Inner Ear Consists of an irregular system of canals and cavities:
- Bony labyrinth(Hard, bony outer shell.)
- Membranous labyrinth(Fully contained inside the bony labyrinth.)
- Bony labyrinth is an example of cartilaginous bone (i.e. a bone which ossification cartilage).
- Vestibule – central chamber of labyrinth. In its lateral wall lies the oval window.
- Semicircular canals.
- Shortest part of VIIth cranial nerve
- Cochlear duct
- Three semicircular canals
- Endolymphatic duct and sac:
- It is formed by union of saccule and utricle
- It connects scala media to subdural space
- Its terminal part is dilated to form the endolymphatic sac
- Endolymphatic sac lies between the two layers of dura on the posterior surface of petrous bone
- Posterior part of vestibule.
- Horizontal acceleration with forward movement in the sagittal plane is detected by it.
- 5 openings of semicirular ducts.
- Utricosaccular duct.
- Lies anterior to utricle opposite the stapes footplate in the bony vestibule.
- Saccule is connected to the cochlea via a thin reunion duct.
- Semicircular ducts
- 3 in number.
- Open into utricle
- Crista ampularis
- Macula is a gelatinous matrix into which hair cells project and which is studded with tiny calcium carbonate granules called otoconia
- Arrangement of stereocilia
- Each row of stereocilia is taller than the next. The tip of each stereocilium is linked to the side of the stereocilium behind it by a tip link. Hair cells
|TYPE 1 HAIR CELLS||TYPE 2 HAIR CELLS|
|Flask shaped cells with a rounded base, narrow neck.||More columnar, kinocilium, sterocilia, cytoplasmic roganelles are similar to type 1.|
|Nucleus is basal, surrounded by mitochondria||Golgi complex is larger, small vesicles found in great numbers in cytoplasm.|
|With supranuclear Golgi complex, occasional cisternae of RER & small vesicles.||Synaptic ribbons are found in the peripheral cytoplasm opposite the plasmalemma of terminal boutons.|
|With 50-100 sterocilia on free surface.
Tallest hair is 10um near kinocilium & shortest is 1um on the opposite side.
|Some endings contain clear synaptic vesicles (non granulated vesicles) carry afferent nerves info to brain.|
- Trautmann’s Triangle:The triangle bounded by the bony labyrinth, sigmoid sinus, and superior petrosal sinus is known as Trautmann’s triangle.
- Snail shaped coiled tube.
- 2.5 to 2.75 turns round a central pyramid of bone called modiolus.
- 30 mm long
- 5 mm from base to apex & 9 mm around its base Anterio medial to vestibule
- Lumen of cochlear canal is partitioned into 3 spiral chambers:
- 1. scala vestibuli (above)Movement of stapes causes vibration in Scala vestibuli.
- 2. scala media (between):Filled with endolymph
- 3. scala tympani (below)
- Central(2, 3/4) pyramid of bone around which cochlea forms
- The base of modiolus directed towards internal acoustic meatus
- Transmits vessels and nerves to cochlea
- Promontary:A bony bulge in the medial wall of middle ear , represents the basal coil of cochlea.
- Central chamber
- Spherical recess-saccule
- Ellipticle recess-utricle
- Osseous spiral lamina
- Bone winds spirally around modiolus .Gives attachment to the basilar membrane and divides the bony cochlea tube into three compartments.
- Basilar membrane,Vestibular membrane, Reissner’s membrane
- Rosenthal’s canal:Spiral ganglions are situated in this canal which runs along the osseous spiral lamina.
- Aqueduct of cochlea
- Scala tympani of internal ear is connected with subarachnoid space via aqueduct of cochlea.
- It is thought to regulate perilymph & pressure in bony labrynth
- Basilar membrane:Has 2 zones:Zona arcuata, Zona pectinata
- Tectorial membrane:Secreted at the upper surface of interdental cells, forms a cuticular layer over these cells
- Organ Of Corti
- The end organ of hearing situated in Scala media
- Inner hair cells - Broad base, resting on the basilar membrane, slender and conical, nucleus is basal.
- Outer hair cells -Longer and more oblique, leaning to the inner pillars.with broad thin base.Otoacoustic emissions arise from it. Sound produced by outer hair cells travels in a reverse direction:Outer hair cells→basilar membrane→ perilymph→ oval window→ ossicles→ tympanic membrane→ ear canal.
- Tunnel of corti- Wide triangular intercellular space continuous through cochlear length. Bounded above converging inner and outer pillar cells.
- Deiters cells -Supporting cells for the 3 -4 rows of outer hair cells.
- Base is columnar with cup shaped upper end.
- The apex does not reach the free surface of the organ of Corti. Inner phalangeal cells - arranged in a row on the inner side of the inner pillar cells.
- Contiguous with slender Border cells marking the inner boundary of the organ of corti. Lining epithelium is low cuboidal or squamous cells.
- Cells of Hensen- Delimit the outer border of the organ of Corti arrange in rows decreasing in height continuous with the cells of Claudius.Supports hair cells.
- Internal auditory canal
- About 1 cm long
- Passes into petrous part of temporal bone in a lateral direction
- Lined by dura
- Vestibulocochlear Nerve
- Facial nerve including nervus intermedius
- Internal auditory artery and vein
- BLOOD SUPPLY OF LABYRINTH:
|ANTERIOR INFERIOR CEREBRAL ARTERY|
|Ant. Vestibular||Common Cochlear|
- Internal auditory vein
- Vein of cochlear aquaduct
- Vein of vestibular aquaduct
- Drain into inferior petrosal and sigmoid sinuses
|Resembles ECF||Resembles ICF|
|Rich in Na+||Rich in K+|
- Otoacoustic emissions arise from Outer hair cells
- Shortest part of VIIth cranial nerve is labryinth canal
- Scala media of the cochlea is filled with a fluid similar to intracellular fluid with high K+ and low Na+
- Labyrinthine artery is a branch of Anterior inferior cerebellar artery
- Vestible is the central chamber of internal ear
- Promontory seen in the middle ear is Basal turn of cochlea
- Inner ear bony labyrinth is Cartilaginous bone
- Cochlear aqueduct Connects internal ear with subarachnoid space
- Organ of corti is situated in Scala media
- Endolymphatic duct connects scala media to subdural space
- Bony labyrinth, sigmoid sinus, and superior petrosal sinus are the boundaries of Trautmann's triangle
- Vestibule, Senicircular canal & cochlea are the structures included in bony labyrinth
- Modiolus is the Central(2, 3/4) pyramid of bone around which cochlea forms
- Sense organ for hearing is Organ of Corti
- Hair cell of organ of Corti is supported by Deiters & Hensen Cells
- Endolymph is rich in K+
- Horizontal acceleration with forward movement in the sagittal plane is detected by utricle
- Movement of stapes causes vibration in Scala vestibuli.
Don't Forget to Solve all the previous Year Question asked on Internal Ear