Three Parts of Ear 1. Inner ear - hearing and equilibrium 2. Middle ear - hearing3. Outer ear - hearing

Outer Ear

Auricle and External acoustic meatus

Auricle: • Composed of elastic cartilage covered in thin skin

• Helix (rim)

• Lobule (earlobe) (no cartilage)

• Directs sound wave into external acoustic meatus External auditory canal:

• Short, curved tube - 2.5cm long

• Extends from auricle to ear drum

• Near auricle framework is elastic cartilage

• Remainder inside temp bone

• Lines skin with ceruminous glands (secrete ear wax, sticky trap for foreign bodies) Tymphanic Membrane (Eardrum)

• Thin CT membrane, vibrates in response to sound

• Transfers sound energy to middle ear ossicles

• Boundary between outer and middle ears

• Connects with pharynx Middle Ear (Tympanic Cavity) Small, air filled, mucosa lined cavity.Petrous portion of temporal bone (laterally by eardrum, flanked medially by bony wall that containts oval (superior) + round (inferior) windows.Epitympanic recess:• RoofofmiddleearPharyngotympanic Tube

• Connects middle ear to nasopharynx

• Equalises pressure in the middle ear cavity with external air pressure

• Eardrum vibrates freely only if pressure on both sides is equal Ear Ossicles Tympanic cavity contains three of the smallest bones in the body 1. Malleus (hammer) - secured to eardrum2. Incus3. Stapes (stirrup) Base fits into oval window - Ligaments suspend the ossicles and synovial joints link them to span the middle ear. - Transmit vibratory motion of eardrum to oval window. Two muscles associated1. Tensor tympani and stapedius (inserts on malleus) 2. Stapedius (inserts on staples)

Dampen sound by tensing ear drum and limiting movement of stapes in oval window.

Inner Ear

Deep in temporal bone behind eye socket.

Bony labyrinth Three regions: Vestibule, cochlear, semicurcular canals Filled with perilymph (very similar to cerebrospinal fluid)

Membranous labyrinth Series of membranous sacs within bony labyrinthSuspended in perilymph and contains endolymph (potassium rich) Fluid of inner ear conduct sound vibrations involved in hearing and respond to mechanical forces during changes in body position and acceleration.

V estibule Central-egg shaped cavity of bony labyrinth- Posterior to cochlear, anterior to semicurcular canals. - Lateral wall is oval window Suspended in the perilymph are two membranous labyrinth sacs Saccule - extends into the cochlearUtricle - Extends into semicircular canalSaccule and utricle house equilibrium receptor regions

- Maculae- Respond to gravity and position of the head

Semicircular Canals Three canals that define 2/3 of a circle and lie in three places of a space - Anterior - Right angles to Posterior in vertical plane- Lateral - lies horizontally- Posterior - Right angles to Anterior in vertical plane Membranous semicircular ducts line each canal and communicate with utricle Ampulla is swollen end of canal. Houses equilibrium receptors in a region called crista ampullaris. Responds to angular movements of the head.

Cochlea Spinal, conical bony chamberExtends from anterior vestibuleCoils around bony pillar called modiolusContains cochlear duct (membranous) - ends at cochlear apex. Contains hearing receptor (Corti). Divided into three chambers:1. Scala Vestibuli: superior to cochlear duct, continuous with vestibule. Contains