Inner Ear and Cochlea Anatomy

Study Notes

The inner ear, also known as the labyrinth, consists of two main parts: the bony labyrinth and the membranous labyrinth.
The bony labyrinth is a series of cavities within the temporal bone. This includes the ampulla, the oval window, and the round window.
The membranous labyrinth is a system of fluid-filled sacs and ducts within the bony labyrinth. It includes the endolymph, the semicircular canals, the utricle, the saccule, the vestibule, the cochlea, the perilymph and the endolymphatic duct.

The cochlea is a spiral-shaped structure that is responsible for hearing. It is filled with fluid called perilymph.
The cochlea is divided into three compartments: the scala vestibuli, the scala media, and the scala tympani
The scala vestibuli is filled with perilymph and is connected to the oval window. It is separated from the scala media by Reissner’s membrane.
The scala media, also known as the cochlear duct, is filled with endolymph. It contains the organ of Corti which is the sensory organ of hearing.
The scala media contains the tectorial membrane, stria vascularis, tunnel fibres, outer hair cells, Deiters cells, and the organ of Corti.
The scala tympani is also filled with perilymph and is connected to the round window. It is separated from the scala media by the basilar membrane.

The vestibular part of the labyrinth is responsible for balance and spatial orientation. It consists of the semicircular canals, the utricle, the saccule, and the cochlea.
Semicircular canals are three fluid-filled tubes that are responsible for detecting rotational movement.
The utricle and saccule are two fluid-filled sacs that are responsible for detecting linear acceleration.
The endolymphatic duct drains endolymph from the labyrinth.

Cochlear duct: The organ of Corti within the cochlear duct is responsible for hearing.
- Organ of Corti detects sound vibrations and transmits this information to the brain.
Saccule: Contains macula that detects vertical linear acceleration.
Utricle: Contains macula that detects horizontal acceleration.
Semicircular canals: Contains crista ampullaris that detects rotational acceleration.

Vertigo is a sensation of spinning or movement, either of your body or your surroundings.
Vertigo is a symptom and not a condition itself.
Vertigo can be caused by a variety of factors, including:
- Benign Paroxysmal Positional Vertigo (BPPV)
- Endolymphatic hydrops (Meniere's Disease)
- Vestibular neuritis
- Labyrinthitis
- Perilymphatic fistula
- Vestibular Schwannoma (Acoustic Neuroma)
Nystagmus (involuntary eye movement) is the only sign of vertigo.

Videonystagmography (VNG) is used to measure eye movements and diagnose vertigo.
Caloric test is used to assess the function of the semicircular canals.
MRI (Magnetic Resonance Imaging) is used to identify any structural abnormalities in the inner ear.