Test: Embryology and Anatomy of Ear - 2 - NEET PG MCQ

• The horizontal/lateral semicircular canal along with posterior and superior semicircular canal contains cristae which sense angular or rotational acceleration.
• Horizontal acceleration, i.e. linear acceleration, gravitational movements and head tilt movements are sensed by maculae in the utricle and saccule.

• The Oval window is covered by the footplate of stapes.
• The Round window is covered by secondary tympanic membrane.
• The part of middle ear medial to the descending part of facial nerve is called sinus tympani.
• Pyramid is the projection on posterior wall from which originates the stapedius muscle.

The electrodes of cochlear implant are placed into the Scala tympani by passing through the round window.

• Perilymph is the fluid which fills the bony labyrinth.
• Perilymph is actually an extension of CSF which enters from the subarachnoid space into the scala tympani through Cochlear aqueduct.
• CSF being an extracellular fluid therefore perilymph is rich in Na+.
• Endolymph filling the membranous labyrinth and secreted from stria vascularis is rich in K⁺.

• Endolymph is present in the membranous labyrinth, whereas perilymph is present in the bony labyrinth.
• Hence scala vestibuli, scala tympani and their interconnection helicotrema, which are parts of bony labyrinth, are filled with perilymph.
• Scala media, utricle, saccule and semicircular canals, which are parts of membranous labyrinth, are filled with endolymph.

Rest are extracellular hence have more of sodium

• The internal ear communicates with the cranium via two openings:
  • Cochlear aqueduct: via this CSF in the subarachnoid space enters scala tympani and becomes perilymph which circulates in the bony labyrinth.
  • Internal acoustic meatus
• Membranous cochlea is a part of membranous labyrinth which is a closed sac and is not connected to vestibule which is a part of the bony labyrinth.
• Endolymphatic sac is a blind pouch responsible for absorption of endolymph and is situated in between the endosteal and meningeal layer of the dura mater.

• • Endolymphatic sac is a closed sac. It does not communicate with CSF.
• The bony canal around the utriculo-saccular duct and endolymphatic duct is called vestibular aqueduct
• Hyrtle fissure is a tympanomeningeal fissure which obliterates by 26 weeks period of gestation.
• If persistent it can lead to a connection between CSF and middle ear.

The skin on the lateral side of pinna is firmly attached because of which any inflammatory condition on the lateral side is more painful.

• Ceruminous glands are modified sudoriferous glands (sweat glands) located subcutaneously in the external auditory canal. They are apocrine glands, i.e. while discharging the secretions their cell’s apical parts are shed off.
• Eccrine or merocrine glands secretions are thrown out of the cells by a process of exocytosis, the cell remaining intact, e.g. sweat glands.
• In some glands the entire cell disintegrates while discharging its secretion. These are said to be holocrine glands, e.g. sebaceous glands.
• Apocrine, merocrine and holocrine are the descriptions of exocrine glands i.e. the glands which pour their secretions on to an epithelial surface directly or through ducts.
• Endocrine glands pour their secretions into blood.

• The notch of Rivinus is the upper attachment of pars flaccida.
• Petro-tympanic fissure is present on the anterior wall of middle ear, on which attaches the anterior malleolar ligament.

Retropharyngeal fissure does not exist.

• Reissner’s membrane separates Scala media from Scala vestibuli in the inner ear.
• Basilar membrane separates Scala media or cochlear duct from Scala tympani in the inner ear. The organ of Corti rests on the basilar membrane.
• Secondary TM overlies the round window in the middle ear.