Functions of the Ear

Outer Ear Structures

Middle Ear Structures

Inner Ear Structures

Functions of the Ear

Ligaments

About the Ossicular Chain

Tympanic muscles

Middle Ear Ossicles

Landmarks of the middle ear (walls)

Functions of the Ear

Ear = energy transducer

Converts acoustic energy into electrochemical energyAcoustics -> mechanical -> electromechanical 3 sections :

• Outer ear - collects and shapes sounds
• Middle Ear - transfers vibrations to oval window to liquidfy
• Inner Ear - converts sound (now in fluid) to electrical code

EAM (Ear Canal)

Concha (or concha auricular) = entrance to the canal Function : EAM & conchae = resonating cavities that contribute to hearing & major determinant for resonant frequency Structure : lateral 1/3 = cartilage; medial 2/3 = bony meatus (temporal bone sandwich)

• S-shaped; medially, forward, & up then down at the juncture
• Isthmus = 2nd constriction; 0.5 cm from the TM

Otoscope = lighted device used to view EAM & TM (& other cavities of the body)

Pinna (auricle)

Cartilaginous Part of the Ear

Primary Function : collector of sound to be processed at the deeper levels/structuresOther functions :

• Aiding in the localization of sound in space
• Capturing sound energy

Tympanic Membrane

AKA Ear Drum

Structure :

• A thin trilaminar sheet of tissue at oblique angle in the EAM

3 layers of thin tissueOuter (cuticular) Layer

• Epithelial cover of the Pinna continues into the EMA
• Epithelial lining of the EAM continuation

Intermediate (fibrous) Layer

• Layer of. Fibrous (strong) tissue for structure
• superficial layer = fibers that radiate out from the handle of the malleus to the periphery of the membrane
• deep layer = circular fibers found in the periphery

Inner (muscous) layer

• continuous with mucose of the middle ear

Landmarks

• umbo = most distal (away from the center) point of attachment of the inner TM to the malleus (middle ear bone)
• the handle (or manubrium) of the malleus behind the TM may appear as a streak on the membrane
• cone of light = where light of otoscope reflects

Malleus

Largest & Point of attach. for TM

anterior & lateral processes = point of attactment for ligamentsmanubrium attaches to TM and ends at the lateral processanterior & posteroir malleolar folds = lateral process P.O.A.Protrudes into the epi(outer most)tympanic recess of the ME

Incus (the anvil)

Function : intermediate communicating link of the ossicular chain the malleus and incus move together as a unit upon movement of the TM

Stapes (AKA stirrup)

Articulates with the lenticular process of the Incus Footplate rests in the oval window of the temporal bone, held in place by annular ligament

Stapes

Middle Ear Ligaments

annular lig. : holds stapes to oval window superior lig. of the malleus : hold malleus in epitympanic recess anterior lig. of the malleus : binds the neck of the mallues to anterior wall of the middle ear lateral lig. of the malleus : attaches head to the later wall posterior lig. of the incus : suspends the incus by the short process superior lig. of the incus : (poorly formed) binds the incus to the epitympanic recess

Tympanic Muscles

Stapedius muscle : Origin : posterior wall of middle ear space of temporal bone Course: anteriorlyInsertion: Posterior crus of stapes Innervation: VII Facial Nerve Fuction: Rotates footplate posteriorly, stiffens chain

Tensor tympani : Origin : Cartilaginous portion of auditory tube & greater wing of sphenoid Course: Posteriorly through canal for TT & around trochleariform processInsertion: PManubrium malli Innervation: V trigeminal nerve via otic ganglion Fuction: Pulls malleus anteromedially and stiffens chain

Together :Fuction: contraction of both muscles reduces the movement and strength of signal reaching cochlea, potentially protecting from damage due to high signal intensity

Note : the TM and ossicles are removed in these diagrams