Hearing

Pinna

Externally visible portion of the outer ear

Tympanic membrane

Barrier between the outer and middle ear

Malleus

Ossicle that connects to the tympanic membrane

Incus

Middle ossicle

Stapes

Ossicle that connects to the oval window

Reissner's membrane

Cochlear membrane that is thin and flexible from the base to the apex

Basilar membrane

Cochlear membrane that is thick and narrow at the base of the cochlea and thin and wide at the apex

Scala vestibuli

Space in the cochlea above reissner’s membrane, connected to the oval window at the cochlear base

Scala tympani

Space in the cochlea below the basilar membrane, connected to the round window at the cochlear base

Helicotrema

Point at the cochlear apex where the scala vestibuli and typmani meet

Scala media

Space in the cochlea between the basilar membrane and reissner’s membrane

Stria vascularis

Epithelial tissue lining the scala media

Perilymph

Fluid of the scala vestibuli and tympani

Endolymph

Fluid of the scala media

Tectorial membrane

Membrane that converts the up-and-down movements of the basilar membrane to back-and-forth movements of the hair cells

Inner hair cells

Row of cells that allow K+ ions to enter the cell when cilia bending outward, largely connected to afferent neurons

Outer hair cells

Rows of cells that enhance the motion of the basilar membrane, largely connected to efferent neurons

Tonotopic encoding

Encoding based on the location of firing hair cells on the basilar membrane, increasing in precision with increasing frequencies

Phase-locked encoding

Encoding based on the speed of firing hair cells, generally limited to < 4 kHz

Intensity encoding

Encoding based on the number of firing hair cells

Auditory nerve fibers

Neurons projecting unilateral auditory information to the ipsilateral brainstem

CN VIII

Region of brainstem that primarily projects unilateral auditory information to the contralateral pons and secondarily to the ipsilateral pons and midbrain

Superior olivary complex

Region of the pons that projects bilateral auditory information to the ipsilateral midbrain

Inferior colliculus

Region of the midbrain that projects bilateral auditory information to the ipsilateral thalamus

Medial geniculate body

Region of the thalamus that projects bilateral auditory information to the primary auditory cortex