M22: Hearing and Vestibulation

Region of the ear containing the auricle and external acoustic meatus

External ear

Functions of the auricle

Gathers and amplifies sound waves while providing directional information

Function of cerumen (ear wax)

Produced in the external acoustic meatus to provide protection and trap debris

Anatomical boundary between the external and middle ear

Tympanic membrane (eardrum)

The three middle ear ossicles from lateral to medial

Malleus,Incus,Stapes

Function of the Pharyngotympanic (Eustachian) tube

Connects the middle ear to the nasopharynx to equalize pressure on both sides of the eardrum

Superior opening where the stapes transmits vibrations to the inner ear

Oval window

Inferior opening that dissipates pressure/vibrations from the inner ear

Round window

Two muscles that contract to protect the ear from loud noises

Stapedius and Tensor tympani

Cavities within the temporal bone filled with perilymph

Bony labyrinth

Tubes and ducts within the bony labyrinth filled with endolymph

Membranous labyrinth

Fluid found outside the membranous labyrinth (similar to CSF)

Perilymph

Fluid found inside the membranous labyrinth (high Potassium concentration)

Endolymph

The three channels (scalae) of the cochlea

Scala vestibuli

Fluid found within the Scala Vestibuli and Scala Tympani

Perilymph

Fluid found within the Cochlear Duct

Endolymph

The membranous labyrinth structure of the cochlea containing the Spiral Organ

Cochlear duct (Scala media)

The sensory receptor for hearing located on the basilar membrane

Spiral Organ (Organ of Corti)

The stationary structure that hair cell stereocilia brush against to trigger a signal

Tectorial membrane

The physical structure that vibrates to push hair cells against the tectorial membrane

Basilar membrane

Mechanism of sound frequency (pitch) perception

Determined by which specific part of the basilar membrane vibrates

Mechanism of sound intensity (loudness) perception

Determined by the total number of hair cells that are stimulated

Step-by-step path of sound waves

Tympanic membrane->Ossicles->Oval window->Perilymph->Endolymph->Basilar membrane->Hair cells

The two main components of the Vestibular Complex

Vestibule (Utricle/Saccule) and Semicircular canals

Specific structure that detects horizontal linear acceleration

Utricle

Specific structure that detects vertical linear acceleration

Saccule

The sensory receptor for static equilibrium (linear movement) found in the vestibule

Maculae

The calcium carbonate crystals that move the gelatinous layer in the maculae

Otoliths

Structure responsible for sensing rotational (dynamic) equilibrium

Semicircular ducts

The expanded region of a semicircular canal containing the sensory receptors

Ampulla

The sensory receptor for rotational movement consisting of hair cells and a cupula

Crista ampullaris

The gelatinous dome in the semicircular canals pushed by endolymph

Cupula

The effect of bending stereocilia toward the kinocilium

Depolarization (excitation/signal)

The neural pathway for hearing (ECOLI)

Cochlear nerve->Cochlear nuclei->Superior olive->Inferior colliculus->MGN->Auditory cortex

Function of the Superior Olivary Nucleus

Sound localization

Function of the Inferior Colliculus

Auditory reflexes (unconscious motor response)

The brainstem structure where the vestibular nerve first synapses

Vestibular nuclei

Vestibular relay destination for coordination and balance

Cerebellum

Vestibular relay destination for conscious awareness of head position

Cerebral cortex (via Thalamus)

Vestibular relay destination for reflexive eye tracking

Cranial nerves III

Vestibular relay destination for head/neck posture and postural muscles

Cranial nerve XI and Spinal cord