ANATOMY OF THE EAR

Pinna

External Auditory Meatus

External Ear Canal

Tympanic Membrane

Middle Ear Walls

Middle Ear Function

Ossicles

Middle Ear Muscles

Energy Changes

Outer, Middle and Inner Ear

Vestibular Mechanism

Cochlea

scala tympani—starts at round window and contains perilymph scala vestibuli—starts at the oval window and also contains perilymph helicotrema—found at the apex of the cochlea where the perilymph from the scala tympani and the scala vestibuli meet. scala media (cochlear duct)—closed at base and at the helicotrema end. This duct contains endolymph which is the same fluid contained within the saccule, utricle, and semicircular canals.

Cochlea

Coil of Cochlea

Scala Media

Cochlea (continued) Ductus reuniens—connects the vestibular areas to the auditory mechanism and allows the endolymph to circulate between these two areas. Basilar membrane—separates scala tympani from scala media Reisner’s membrane—separates scala vestibuli from scala media

Organ of Corti Organ of Corti—end organ of hearing. Found in the scala media Rods of Corti—form the tunnel of Corti. On each side of the rods are found hairs arranged in an orderly fashion. One row of inner hair cells (3,000) and three rows of outer hair cells (12,000—15,000). Tectorial membrane—hair cells are imbedded in this jelly-like membrane after they pass through the reticular lamina. Hensen cells—supportive to the hair cells Stria vascularis—produces endolymph and is responsible for getting oxygen and blood to the Organ of Corti. Found on the lateral wall of the cochlear duct.

Organ of Corti

Cochlea Unrolled

Frequency Specific

Cochlea Cochlea is frequency specific - basal end is responsible for the high frequencies and apical end controls low frequencies.

Auditory Nerve Internal auditory Meatus (IAM) - nerve fibers pass from the modiolus through the IAM to the base of the brain. VIII Nerve is comprised of 30,000 nerve fibers from the cochlea + 20,000 from the vestibular and travel through the IAM to the brain stem.

Auditory Pathways

Cochlea hair cells Auditory nerve fibers Cochlear nucleus Trapezoid body Superior olivary complex Lateral lemniscus Inferior coliculus Medial geniculate body Auditory cortex