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Functions of the ear

Hearing and balance

Three areas of the ear

External, middle, and inner

External Ear

Auricle, external auditory canal, tympanic membrane

Auricle (pinna)

Elastic cartilage

External auditory canal (meatus)

Within the temporal lobe, ceruminous glands

Tympanic membrane

Separates external and middle ear, fibrous CT

Middle Ear

Ossicles, openings, muscles

Ossicles

Malleus, incus, stapes

Three openings

Oval window- Superior, stapes rests on it
Round window- Inferior
Pharynogotympanic (auditor) tube, or Eustachain tube- Connects with nasopharynx

Muscles

Stapedius, tensor tympani

Inner ear

Bony labyrinth, membranous labyrinth

Bony labyrinth

Made from petrous portion of temporal lobe, filled with perilymph, consists of: cochlea, 3 semicircular canals, vestibule

Membranous labyrinth

Filled with endolymph, consists of: cochlear duct (w/in cochlea), 3 semicircular ducts, utricle and saccule

Cochlea

Bony upper scala vestibuli and lower scala tympani: filled with perilymph. Middle membranous scala media or cochlear duct contains Organ of Corti; filled with endolymph. Upper vestibular membrane and lower basilar membrane which supports Organ of Corti

Organ of Corti

Rests upon basilar membrane, has supporting cells, hair cells (inner and outer), tectorial membrane on top of hairs, cochlear branch of vestibulocochlear nerve cranial nerve VIII

Physiology of Hearing

Passage of sound waves
Pressure waves in cochlea
Movement of hairs in Organ of Corti
Depolarization and passage of impulse
High frequency sound-stimulate hair cells near oval window; low frequency near apex

Equilibrium

Vestibular branch of VIII cranial nerve
Static Equilibrium
Dynamic Equilibrium

Static Equilibrium

Role of macula in utricle and saccule within vestibule
Otolithic membrane

Dynamic Equilibrium

Role of semicircular ducts with semicircular canals
Ampulla at base containing crista ampularis

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