a n a t o m y o f I n n e r E a r.pptx

anatomy of inner ear

1. Inner Ear

2. Inner Ear Site : It lies in the petrous part of the temporal bone. Parts : formed of bony part and membranous part.

3. Inner Ear A- Bony part (osseous labyrinth), formed of: 1) Cochlea: - A snail shaped cavity in front of the vestibule. - The cochlea consists of a central pillar called modiolus, and a bony cochlear canal 2) Vestibule: - It is ovoid cavity of bony labyrinth between cochlea in front and three semicircular canals behind. - It lies medial to the middle ear cavity. - It communicates anteriorly with the cochlea and posteriorly with semicircular canals.

4. 3) Semicircular canals: - They are three inverted U shaped canals (superior, posterior, and lateral). - Each canal is dilated at one end forming the ampulla. - They lie in three planes at right angles to each other. - Each canal is about two-third of a circle. - There is fusion between one limb of the superior and one limb of the posterior semicircular canals forming the crus commune.

5. Inner Ear B- Membranous part (membranous labyrinth) - A single continuous tubular structure inside the bony labyrinth. - It is formed of: 1) Cochlear duct (within the cochlear canal -Concerned with hearing). 2) Utricle and saccule (within the vestibule -Concerned with static balance). 3) Semicircular ducts (within the semicircular canals -Concerned with kinetic balance).

6. Inner Ear Sensory receptors inside membranous labyrinth 1) Organ of Corti : In the cochlea  Function: Hearing (it contains the dendrites of the spiral ganglion). 2) Macula utriculi and macula saccule:  In the utricle and saccule respectively.  Function: static balance (they are innervated by the vestibular nerve). 3) Crista ampularis:  In the semicircular canals.  Function: kinetic balance (it is innervated by the vestibular nerve)

7. Inner Ear

8. Inner Ear Blood supply of the labyrinth: a) Arterial supply 1) Labyrinthine artery (from the basilar artery). 2) Stylomastoid artery. b) Venous drainage  Labyrinthine vein which passes through the internal acoustic meatus to join the inferior petrosal sinus (small veins drain into the superior petrosal sinus).

9. The Vestibulocochlear Nerve (CN VIII)

10. Type: purely special sensory nerve consists of two parts: a. Vestibular part, called the vestibular nerve, concerned with the maintenance of equilibrium b. Cochlear part, called the cochlear nerve, concerned with hearing. - Origin : arises from the lateral aspect of the pontomedullary junction.

11. Functional Components and Nuclei: Special somatic afferent fibres:  They carry sensory information necessary for the maintenance of equilibrium and hearing from the membranous labyrinth of the internal ear.  The fibres carrying the sensory information for equilibrium terminate in the vestibular nuclei within the brainstem.  The fibres carrying the sensory information for hearing terminate in the dorsal and ventral cochlear nuclei, located respectively on the dorsal and ventral aspects of the inferior cerebellar peduncle.

12. Course and relation:  The vestibular and cochlear portions of the vestibulocochlear nerve are functionally discrete, and so originate from different nuclei in the brain: a. Vestibular component: arises from the vestibular nuclei complex in the pons and medulla. b. Cochlear component: arises from the ventral and dorsal cochlear nuclei, situated in the inferior cerebellar peduncle

13.  Both sets of fibres combine in the pons to form the vestibulocochlear nerve. The nerve emerges from the brain at the cerebellopontine angle and exits the cranium via the internal acoustic meatus of the temporal bone.  Within the distal aspect of the internal acoustic meatus, the vestibulocochlear nerve splits, forming the vestibular nerve and the cochlear nerve.

14. a. The vestibular nerve: In the lateral part of the internal acoustic meatus, the nerve divides into three distinct branches: superior and inferior divisions and singular nerve. These branches pass through the foramina in the fundus of the meatus and innervate the sensory receptors for equilibrium (cristae ampullaris and maculae) in the membranous labyrinth of the internal ear. b. The cochlear nerve travels to cochlea of the inner ear, forming the spiral ganglia, which innervates the sensory receptor of hearing the organ of Corti.