Hearing and Vestibular Sense

Vestibular sense

our ability to both detect rotational and linear acceleration and to use this information to inform our sense of balance and spatial orientation

Three parts of the ear

outer, middle , and inner

Outer ear

consists of the pinna (auricle), external auditory canal, and tympanic membrane

Pinna (auricle)

the cartilaginous outside part of the ear; its main function is to channel sound waves into the external auditory canal

External auditory canal

directs the sound waves to the tympanic membrane

Tympanic membrane (eardrum)

Divides the outer ear from the middle ear. It vibrates in phase with the incoming sound waves; the faster the vibration, the higher the pitch. The intensity (or amplitude) of the vibration depends on the loudness of sounds coming into the ear

Middle ear

consists of the ossicles (3 smallest bones in the body): malleus (hammer), incus (anvil), and stapes (stirrup)

Ossicles

help transmit and amplify the vibrations from the tympanic membrane to the inner ear

Malleus (hammer)

connects to the tympanic membrane, transferring sound vibrations to the incus

Incus (anvil)

transmits sound vibrations from the malleus to the stapes

Stapes (stirrup)

transmits sound vibrations from the incus to the cochlea

Oval window of the cochlea

the entrance to the inner ear

Eustachian Tube

connects the middle ear to the nasal cavity, which helps equalize pressure between the middle ear and the environment

Bony labyrinth

where the inner ear sits in; it is a hollow region of the temporal bone containing the cochlea, vestibule, and semicircular canals

Membranous labyrinth

a continuous collection of tubes and chambers in the bony labyrinth; this collection of structures contains receptors for the sense of equilibrium and hearing

Endolymph

a potassium-rich fluid in the membranous labyrinth that aids in the hearing and equilibrium

Perilymph

fluid in the bony labyrinth that simultaneously transmits vibrations from the outside world and cushions the inner ear structures

Cochlea

a spiral-shaped organ that contains the receptors for hearing

Vestibule

portion of the bony labyrinth that contains the utricle and saccule; these structures detect linear acceleration

Semicircular Canals

detects rotational acceleration

Auditory pathways

goes from the cochlea and through the vestibulocochlear nerve and medial geniculate nucleus (MGN) of the thalamus to get to the auditory cortex in the temporal lobe; some information is also sent to the superior olive and inferior colliculus

Superior olive

localizes sound

Inferior colliculus

involved in the startle reflex and helps keep the eyes fixed on a point while the head is turned (vestibulo ocular reflex)