AUDITORY APPARATUS Mr. P Mazengenya Tel 72204
Describe the anatomical features of the external ear Describe the tympanic membrane (ear drum) Describe the walls of the middle ear Outline the structures located within the middle ear Understand the transmission of sound through the middle ear Describe the bony labyrinth and its components Describe the membranous labyrinth and its components Understand the organization of the semicircular canals and their relationship to equilibrium Understand the organization of the Organ of Corti and its relationship to hearing Understand how sound is perceived AIMS
The ear : o Divided into: External ear Middle ear Inner ear
External ear o Auricle or pinna Skin-covered elastic cartilage Collects sound and directs it to external auditory meatus o External auditory (acoustic) meatus From the deepest part of the concha to the tympanic membrane
Auricle
External ear o Lateral ⅓ cartilagenous normal skin o Medial ⅔ bone thin skin Lateral ⅓ o Ceruminous glands sebaceous glands o Hairs
Tympanic membrane o Forms medial wall external ear, lateral wall of middle ear o Oval and semitransparent o Covered with thin skin externally and mucous membrane internally o Umbo related to the lateral process of the malleus
Tympanic membrane o Moves in response to air vibrations o Transmits vibrations to auditory ossicles of middle ear via handle of malleus
Innervation to the external ear
Middle ear o Contained within petrous part of temporal bone o Includes tympanic cavity and epitympanic recess o connected with nasopharynx by pharyngotympanic tube (auditory canal)
Contains o Auditory ossicles (bones of middle ear) Malleus Incus Stapes o Stapedius and tensor tympani muscles o Chorda tympani nerve o Tympanic plexus (nerves)
Tympanic cavity
Walls of tympanic cavity: o Roof Thin bone-tegmen tympani Separates tympanic cavity from middle cranial fossa o Floor Bony Separates tympanic cavity from superior bulb of internal jugular vein
o Medial wall Separates tympanic cavity from inner ear Features Promontory: round projection overlying basal turn of cochlea Oval window into which footplate of stapes fits-secondary tympanic membrane Fenestra cochlea or round window
Anterior wall o Separates tympanic cavity from carotid canal o Superiorly has opening of auditory tube and canal for tensor tympani
o Posterior wall Superiorly, aditus (opening) to mastoid antrum, connecting to mastoid air cells Between posterior wall and aditus, prominence of canal of facial nerve Pyramidal eminence Tiny cone-shaped prominence Contains proximal attachment of stapedius muscle
Posterior wall
o Lateral wall Tympanic membrane Lateral wall of epitympanic recess Handle of malleus
Auditory ossicles
o Chain of bones across tympanic cavity o Extend from tympanic membrane to oval window on medial wall o Increase the force but decrease amplitude of vibrations from tympanic membran
Auditory tube o Eustachian tube o Communication between middle ear and nasopharynx o Allow equalisation of atmospheric pressure in middle ear o Actively opened by coordinated contractions palatine muscles
Muscles o Function to dampen movement of auditory ossicle o Tensor tympani o Stapedius
Nerves o Chorda tympani Branch of facial nerve (cranial nerve [CN]) VII o Tympanic plexus On the promontory of the medial wall Contributions from tympanic branch of glossopharyngeal (CN IX) Twigs from internal carotid plexus Twig from facial nerve
Inner ear Concerned with the reception of sound o maintenance of balance Lies in petrous portion of temporal bone Membranous labyrinth Inside bony labyrinth
Bony labyrinth o Occupies lateral region of petrous ridge of temporal bone o Space filled with perilymph o Surrounded by bony capsule harder than petrous bone o Cochlea
o Cochlea Consists of Spiral canal Bony core, the modiolus Concerned with hearing Contains the membranous cochlear duct promontory of medial wall of tympanic cavity cochlear aqueductsubarachinoid space
Bony labyrinth o Vestibule Small oval chamber Contains membranous Utricle saccule Oval window is on lateral wall Continuous with Cochlea anteriorly Semicircular canals posteriorly
o Semicircular canals Anterior, posterior, and lateral Each opens into vestibule ampulla Contain membranous semicircular ducts
Membranous labyrinth o Collection of ducts and sacs o Suspended within bony labyrinth o Filled with endolymph
o Vestibular labyrinth Utricle Macula hair cells, sensory epithelium innervated by vestibular division of vestibulocochlear nerve (CN VIII) Hairs respond to tilting of head and acceleration and deceleration Saccule Communicates with utricle Continuous with cochlear duct Contains macula Semicircular ducts Within semicircular canals Hair cells in crest innervated by vestibular nerve Detect rotational (tilting) movements of head
o Cochlear labyrinth Cochlear duct Filled with endolymph Two channels: scala tympani scala vestibule, helicotrema
COCHLEA DUCT Roof of duct = vestibular membrane Floor of duct = basilar membrane
Spiral organ of Corti Found on basilar membrane Covered by tectorial membrane Contains hair cells innervated by cochlear nerve
Propagation of sound o Initiated by sound waves Transmitted as vibrations by ossicles Stapes vibrates in oval window o Reception of sound Deformation of cochlear duct by pressure waves in perilymph Stimulates hair cells of spiral organ embedded in tectorial membrane
Sound progation
Summary Ear External Middle Inner Understand the walls of the middle ear Inner bony and membranous parts Otitis media auditory tube Braches of the facial nerve chorda tympani