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

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 planeLateral - 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