Inner Ear

Scala media

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

Scala vestibuli

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

Scala tympani

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

Basilar membrane

Membrane responsible for frequency discrimination

Cochlear apex

The end of the cochlea with a thin wide basilar membrane

Cochlear base

The front of the cochlea with a thick narrow basilar membrane

Inner hair cells

Row of cells that allow K⁺ ions to enter the cell when cilia bend towards the tallest cilia, largely connected to afferent neurons

Outer hair cells

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

Spontaneous firing

Nerve fibers firing at 0 dB

High SR nerve fibers

Nerve fibers detecting volume of stimuli at <40 dB, producing a linear response to the characteristic frequency

Low SR nerve fibers

Nerve fibers detecting volume of stimuli at >40 dB, producing a compressed response to the characteristic frequency

Stimulus onset

Time of greatest firing rate

Single nerve fiber response

Firing rate related to stimulus amplitude

Pooled nerve fiber response

Firing rate related to stimulus frequency and extreme stimulus amplitude

Superior olive

Part of the brainstem that compare information between ears

Basilar membrane peak shift

Decreasing peak frequency with increasing amplitude at a given spot on the basal basilar membrane

Iso-level curves

Curves measuring basilar membrane velocity over frequency for a set of stimulus amplitudes

Tuning curves

Curves measuring stimulus amplitudes over frequency for a set of basilar membrane velocity

Characteristic frequency

Frequency that the basilar membrane is most responsive to at a low level dB SPL

Active mechanism of outer hair cells

Increased velocity response at low intensity and decreased velocity response at high intensity for the characteristic frequency

Passive mechanism of outer hair cells

Linear response to the characteristic frequency

Olivocochlear efferent fibers

Neurons responsible for characteristic frequency compression

Two-tone suppression

Suppression of a tone when a tone with a similar frequency is added

Lateral inhibition

Two-tone suppression of further tones resulting in a narrowing tuning curve