A cortex of bone with honeycomb of air cells underneath.3 types
1.Well pneumatized/cellular-mastoid cells well developed,intervening septa thin
2.Diploetic-mastoid contains marrow spaces,few air cells
3.Sclerotic/acellular-No cells in marrow spaces-antrum small,sigmoid sinus antepositioned
Location wise, the nomenclature is:
1.zygomatic cells-root of zygoma
2.tegmen cells-extending in tegmen tympani
3.perisinus cells-overlying sinus plate
4.retrofacial cells-round the facial nerve
5.perilabyrinthine-above,below&behind labyrinth,some passing through arch of superior semicircular canal-may communicate with the petrous apex
6.peritubal-around eustachian tube-along with hypotympanic cells, may communicate with petrous apex
7.tip cells-large & lie medial & lateral to the digastric ridge in the tip of mastoid
8.marginal cells-lying behind sinus plate,may extend into occipital plate
9.squamosal cell-lying in squamous part of temporal bone-superficial
Development:
superficial-squamous
deep-petrous
petrosquamosal suture may persist as a bony plate- korner's septum- may cause difficulty in locating deeper structures like antrum & other deeper cells
Ear Ossicles:
Malleus- head,neck,handle(manubrium),lateral & anterior process- head& neck lie in attic,manubrium embeded in fibrous layer of TM. The lateral process forms a knob like projection on outer surface of TM & gives attachment to anterior & posterior malleal folds.
Incus-body, short process, long process-hangs vertically to attach head of stapes
Stapes-head, neck, anterior & posterior crura, footplate-held in oval window by annular ligament
Intratympanin muscles:
tensor tympani-1st arch muscle-mandibular nerve(V3)-attaches to neck of malleus & tenses TM
stapedius-2nd arch muscle-CN VII-attaches to neck of stapes-dampens loud sounds-prevents noise trauma to inner ear
Tympanic Plexus:
1.tympanic branch of glossopharyngeal(CNIX)
2.sympathetic fibres from plexus around carotid artery
-supplies innervation to medial surface of TM, tympanic cavity,mastoid air cells & bony eustachian tube
-also carries secretomotor fibres to parotid
Section of tympanic branch of CNIX can be carried out in middle ear in Frey's syndrome
Course of secretomotor fibres to parotid:
Inferior salivary nucleus-CNIX-tympanic branch-tympanic plexus-lesser petrosal nerve-otic ganglion-auriculotemporal nerve-parotid gland
Chorda tympani nerve:
A branch of the facial nerve which enters the middle ear through posterior canaliculus-runs on the medial surface of TM between the handle of malleus & long process of incus, above the attachment of tendon of tensor tympani.Carries taste from anterior 2/3rd of tongue & secretomotor fibres to the submaxillary & sublingual gland
Middle Ear cleft: lining
Mucous membrane of nasopharynx is continuous with that of the middle ear, aditus, antrum & mastoid air cells-it wraps the middle ear structures-ossicles,muscles,nerves,ligaments- like peritoneum wraps various viscera in the abdomen, raising several folds & dividing the middle ear into various compartments-cavity contain air only
eustachian tube-ciliated
pseudostratified columnar in the cartilaginous part
columnar in bony part with several mucous glands in submucosa
Tympanic cavity-
ciliated columnar epithelium in anterior & inferior part
changes to cuboidal in posterior part
epitympanum & mastoid air cells are lined by flat, non ciliated epithelium
Lymphatics:
middle ear- retropharyngeal & parotid nodes
eustachian tube-retropharyngeal group
Internal Ear: hearing & equilibrium:
Bony labyrinth- contains perilymph- vestibule, semicircular canal, cochlea
membranous labyrinth-endolymph-
Vestibule-
central chamber of labyrinth-
lateral wall oval window
inside of medial wall- 2 recesses: elliptical- lodges utricle; spherical- lodges saccule
aqueduct of vestibule- below elliptical recess- passes the endolymphatic duct
posterosuperior part of vestibule-5 openings of semicircular canal
Semicircular canal-
3 in number- lateral,posterior,superior-5 openings
lie in planes@right angles to each other
ampulated ends open independently into vestibule
non-ampulated ends of posterior & superior semicircular canals unite to form- crus commune
Cochlea-
2.5-2.75 turns
central pyramid-bony modiolus-base directed towards internal acoustic meatus-transmits vessels & nerves to cochlea
Arould modiolus- thin plate of bone- osseous spiral lamina- divides bony cochlea incompletely & gives attachment to basilar membrane
promontory- due to basal coil of cochlea
3 compartments-scala vestibuli, scala tympani,scala media
scala vestibuli & scala tympani filled with perilymph- joined@ apex of cochlea- by helicotrema
scala vestibuli closed by footplate of stapes
scala tympani closed by secondary tympanic membrane- also connects subarachnoid space through the aqueduct of cochlea
Membranous labyrinth:
Cochlear duct-membranous cochlea/scala media- a blind coiled tube- triangular C/S
a.basilar membrane- supports organ of corti-separates from scala tympani
b.reissner's membrane-separates from scala vestibuli
c.stria vascularis-contains vascular epithelium & connected with secretion of endolymph
cochlear duct connected to saccule-by ductus reuniens
length of basilar membrane increases as we proceed from basal coil to apical coil
Utricle & saccule:
utricle lies in posterior part of bony vestibule-receives 5 openings of 3 semicircular ducts
connected to saccule through utriculosaccular duct
sensory epithelium-macula- related to linear acceleration/deceleration
saccule lies anterior to utricle-opposite to stapes footplate- sensory epithelium- macula
In Menier's disease, distended saccule lies against the stapes footplate & can be surgically decompressed by perforating the footplate
The ampullated end of semicircular ducts contains a thickened ridge of neuroepithelium- crista ampullaris
Endolymphatic duct-formed by the union of two ducts, one each from the saccule & the utricle-passes through vestibular aqueduct-terminal part dilated-endolymphatic sac-lies between 2 layers of dura on the posterior surface of petrous bone.
Endolymphatic sac is exposed for drainage/shunt operation in Menier's disease
Blood Supply to Labyrinth:
The entire labyrinth receives arterial supply from internal auditory(labyrinthine)artery-branch of anterior inferior cerebellar artery(sometimes basilar artery)
Divides into anterior vestibular & common cochlear arteries.Common cochlear artery further divides into cochlear & posterior vestibular arteries.No collateral circulation in cochlea.
Venous drainage by 3 veins:internal auditory vein, vein of cochlear aqueduct, vein of vestibular aqueduct
1.Well pneumatized/cellular-mastoid cells well developed,intervening septa thin
2.Diploetic-mastoid contains marrow spaces,few air cells
3.Sclerotic/acellular-No cells in marrow spaces-antrum small,sigmoid sinus antepositioned
Location wise, the nomenclature is:
1.zygomatic cells-root of zygoma
2.tegmen cells-extending in tegmen tympani
3.perisinus cells-overlying sinus plate
4.retrofacial cells-round the facial nerve
5.perilabyrinthine-above,below&behind labyrinth,some passing through arch of superior semicircular canal-may communicate with the petrous apex
6.peritubal-around eustachian tube-along with hypotympanic cells, may communicate with petrous apex
7.tip cells-large & lie medial & lateral to the digastric ridge in the tip of mastoid
8.marginal cells-lying behind sinus plate,may extend into occipital plate
9.squamosal cell-lying in squamous part of temporal bone-superficial
Development:
superficial-squamous
deep-petrous
petrosquamosal suture may persist as a bony plate- korner's septum- may cause difficulty in locating deeper structures like antrum & other deeper cells
Ear Ossicles:
Malleus- head,neck,handle(manubrium),lateral & anterior process- head& neck lie in attic,manubrium embeded in fibrous layer of TM. The lateral process forms a knob like projection on outer surface of TM & gives attachment to anterior & posterior malleal folds.
Incus-body, short process, long process-hangs vertically to attach head of stapes
Stapes-head, neck, anterior & posterior crura, footplate-held in oval window by annular ligament
Intratympanin muscles:
tensor tympani-1st arch muscle-mandibular nerve(V3)-attaches to neck of malleus & tenses TM
stapedius-2nd arch muscle-CN VII-attaches to neck of stapes-dampens loud sounds-prevents noise trauma to inner ear
Tympanic Plexus:
1.tympanic branch of glossopharyngeal(CNIX)
2.sympathetic fibres from plexus around carotid artery
-supplies innervation to medial surface of TM, tympanic cavity,mastoid air cells & bony eustachian tube
-also carries secretomotor fibres to parotid
Section of tympanic branch of CNIX can be carried out in middle ear in Frey's syndrome
Course of secretomotor fibres to parotid:
Inferior salivary nucleus-CNIX-tympanic branch-tympanic plexus-lesser petrosal nerve-otic ganglion-auriculotemporal nerve-parotid gland
Chorda tympani nerve:
A branch of the facial nerve which enters the middle ear through posterior canaliculus-runs on the medial surface of TM between the handle of malleus & long process of incus, above the attachment of tendon of tensor tympani.Carries taste from anterior 2/3rd of tongue & secretomotor fibres to the submaxillary & sublingual gland
Middle Ear cleft: lining
Mucous membrane of nasopharynx is continuous with that of the middle ear, aditus, antrum & mastoid air cells-it wraps the middle ear structures-ossicles,muscles,nerves,ligaments- like peritoneum wraps various viscera in the abdomen, raising several folds & dividing the middle ear into various compartments-cavity contain air only
eustachian tube-ciliated
pseudostratified columnar in the cartilaginous part
columnar in bony part with several mucous glands in submucosa
Tympanic cavity-
ciliated columnar epithelium in anterior & inferior part
changes to cuboidal in posterior part
epitympanum & mastoid air cells are lined by flat, non ciliated epithelium
Lymphatics:
middle ear- retropharyngeal & parotid nodes
eustachian tube-retropharyngeal group
Internal Ear: hearing & equilibrium:
Bony labyrinth- contains perilymph- vestibule, semicircular canal, cochlea
membranous labyrinth-endolymph-
Vestibule-
central chamber of labyrinth-
lateral wall oval window
inside of medial wall- 2 recesses: elliptical- lodges utricle; spherical- lodges saccule
aqueduct of vestibule- below elliptical recess- passes the endolymphatic duct
posterosuperior part of vestibule-5 openings of semicircular canal
Semicircular canal-
3 in number- lateral,posterior,superior-5 openings
lie in planes@right angles to each other
ampulated ends open independently into vestibule
non-ampulated ends of posterior & superior semicircular canals unite to form- crus commune
Cochlea-
2.5-2.75 turns
central pyramid-bony modiolus-base directed towards internal acoustic meatus-transmits vessels & nerves to cochlea
Arould modiolus- thin plate of bone- osseous spiral lamina- divides bony cochlea incompletely & gives attachment to basilar membrane
promontory- due to basal coil of cochlea
3 compartments-scala vestibuli, scala tympani,scala media
scala vestibuli & scala tympani filled with perilymph- joined@ apex of cochlea- by helicotrema
scala vestibuli closed by footplate of stapes
scala tympani closed by secondary tympanic membrane- also connects subarachnoid space through the aqueduct of cochlea
Membranous labyrinth:
Cochlear duct-membranous cochlea/scala media- a blind coiled tube- triangular C/S
a.basilar membrane- supports organ of corti-separates from scala tympani
b.reissner's membrane-separates from scala vestibuli
c.stria vascularis-contains vascular epithelium & connected with secretion of endolymph
cochlear duct connected to saccule-by ductus reuniens
length of basilar membrane increases as we proceed from basal coil to apical coil
Utricle & saccule:
utricle lies in posterior part of bony vestibule-receives 5 openings of 3 semicircular ducts
connected to saccule through utriculosaccular duct
sensory epithelium-macula- related to linear acceleration/deceleration
saccule lies anterior to utricle-opposite to stapes footplate- sensory epithelium- macula
In Menier's disease, distended saccule lies against the stapes footplate & can be surgically decompressed by perforating the footplate
The ampullated end of semicircular ducts contains a thickened ridge of neuroepithelium- crista ampullaris
Endolymphatic duct-formed by the union of two ducts, one each from the saccule & the utricle-passes through vestibular aqueduct-terminal part dilated-endolymphatic sac-lies between 2 layers of dura on the posterior surface of petrous bone.
Endolymphatic sac is exposed for drainage/shunt operation in Menier's disease
Blood Supply to Labyrinth:
The entire labyrinth receives arterial supply from internal auditory(labyrinthine)artery-branch of anterior inferior cerebellar artery(sometimes basilar artery)
Divides into anterior vestibular & common cochlear arteries.Common cochlear artery further divides into cochlear & posterior vestibular arteries.No collateral circulation in cochlea.
Venous drainage by 3 veins:internal auditory vein, vein of cochlear aqueduct, vein of vestibular aqueduct
No comments:
Post a Comment