4. Anatomy and physiology of the inner ear. Methods of examination. Otosclerosis. Clinical complications.

Anatomy https://www.youtube.com/watch?v=XPHuiYInOsg

• petrous part of the temporal bone
• Consists of multiple interconnected known as the labyrinth
• The bony labyrinth accommodates the membranous labyrinth

Membranous labyrinth – Endolymph K⁺

• Closed system of intercommunicating membranous sacs & ducts, which lie within the bony labyrinth
• Filled with a potassium-rich fluid (the endolymph)
• Contains cilia-bearing sensory cells → hair cells (Inner hair cells (sensitive to loud sounds) are rounded and outer hair cells (sensitive to softer sound)) are cylindrical)

Composed of:

1. Utricle
2. Saccule

1 & 2 – lies within bony Vestibular Labyrinth; 3 – Lies within bony Cochlear; 4 – Lies within bony Semicircular canals

Utricle and saccule are connected by the utriculosaccular duct

3. Cochlear duct - Between Scala vestibuli and Scala tympani

Cochlear duct and Saccule are connected by ductus reuniens

1. 4. 3 x Semicircular ducts (Anterior, Posterior, lateral)

Utricle and Semicircular ducts connect through five openings, dilated end is called ampulla

• Maculae- Sensory receptors medial wall of saccule & utricle → Static balance
• Cristae – Sensory receptors ampullae ends → Kinetic balance

• Cochlear duct contains Spiral Organ of Corti→ Sensory receptor for hearing

lies on basilar membrane

• Arising from the utriculosaccular duct is the endolymphatic duct (vestibular aqueduct)
• extends to the endolymphatic sac on the posterior surface of the petrous bone, where it is in contact with the dura mater

N: B: Pathway for intracranial extension of temporal bone infections

1. Endolymphatic duct
2. Perilymphatic duct
3. Fallopian channel
4. Internal acoustic meatus

Function of Endolymphatic duct:

1. Absorptive
2. Secretory
3. Phagocytic
4. Immunodefensive

Bony Labyrinth – Perilymph Na⁺

• Separated from the membranous labyrinth by a space filled with perilymph
• Composition of perilymph is similar to extracellular fluid (Sodium-rich)

Subdivided into 3 bony parts:

1. a. Semi-circular canal system – Balance- sensitive to angular acceleration
2. b. Cochlea - Hearing
3. c. Vestibule - Balance — Sensitive to linear acceleration

• Cochlea base is most responsive to high-pitched sounds, while the apex is most responsive to low-pitched sounds
• Cochlear duct is attached between the inner and outer walls of the bony cochlea, creating two separate ducts called the Scala vestibuli and Scala tympani
• Scala vestibuli and Scala tympani are connected at the cochlear apex by the helicotrema
• The oval window – Scala vestibuli: links the inner ear to the middle ear is covered by the stapes footplate and represents the ‘acoustic entrance’ of the labyrinth