Summarizing Hearing and Vestibular Sensation

Summary

Audition is important for territory defense, predation, predator defense, and communal exchanges. The vestibular system, which is not auditory, detects linear acceleration and angular acceleration and deceleration. Both the auditory system and vestibular system use hair cells as their receptors.

Auditory stimuli are sound waves. The sound wave energy reaches the outer ear (pinna, canal, tympanum), and vibrations of the tympanum send the energy to the middle ear. The middle ear bones shift and the stapes transfers mechanical energy to the oval window of the fluid-filled inner ear cochlea. Once in the cochlea, the energy causes the basilar membrane to flex, thereby bending the stereocilia on receptor hair cells. This activates the receptors, which send their auditory neural signals to the brain.

The vestibular system has five parts that work together to provide the sense of direction, thus helping to maintain balance. The utricle and saccule measure head orientation: their calcium carbonate crystals shift when the head is tilted, thereby activating hair cells. The semicircular canals work similarly, such that when the head is turned, the fluid in the canals bends stereocilia on hair cells. The vestibular hair cells also send signals to the thalamus and to somatosensory cortex, but also to the cerebellum, the structure above the brainstem that plays a large role in timing and coordination of movement.

Glossary

audition

sense of hearing

basilar membrane

stiff structure in the cochlea that indirectly anchors auditory receptors

cochlea

whorled structure that contains receptors for transduction of the mechanical wave into an electrical signal

incus

(also, anvil) second of the three bones of the middle ear

inner ear

innermost part of the ear; consists of the cochlea and the vestibular system

labyrinth

bony, hollow structure that is the most internal part of the ear; contains the sites of transduction of auditory and vestibular information

malleus

(also, hammer) first of the three bones of the middle ear

middle ear

part of the hearing apparatus that functions to transfer energy from the tympanum to the oval window of the inner ear

organ of Corti

in the basilar membrane, the site of the transduction of sound, a mechanical wave, to a neural signal

ossicle

one of the three bones of the middle ear

outer ear

part of the ear that consists of the pinna, ear canal, and tympanum and which conducts sound waves into the middle ear

oval window

thin diaphragm between the middle and inner ears that receives sound waves from contact with the stapes bone of the middle ear

pinna

cartilaginous outer ear

semicircular canal

one of three half-circular, fluid-filled tubes in the vestibular labyrinth that monitors angular acceleration and deceleration

stapes

(also, stirrup) third of the three bones of the middle ear

stereocilia

in the auditory system, hair-like projections from hair cells that help detect sound waves

tectorial membrane

cochlear structure that lies above the hair cells and participates in the transduction of sound at the hair cells

tympanum

(also, tympanic membrane or ear drum) thin diaphragm between the outer and middle ears

ultrasound

sound frequencies above the human detectable ceiling of approximately 20,000 Hz