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Exercise 25 Special Senses: Hearing and Equilibrium

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Auricle (pinna)

External acoustic meatus

Tympanic membrane

structures composing the external ear


Semicircular canals



structures composing the internal ear


Incus (anvil)

Malleus (hammer)

Stapes (stirrup)

collectively called the ossicles


Pharyngotympanic (auditory) tube

- involved in equalizing the pressure in the middle ear with atmospheric pressure

- passage between the throat and the tympanic cavity


Tympanic membrane

vibrates at the same frequency as sound waves hitting it; transmits the vibrations to the ossicles


Semicircular canals


contain receptors for the sense of balance


Oval window

transmits the vibratory motion of the stirrup to the fluid in the scala vestibuli of the internal ear


Round window

acts as a pressure relief valve for the increased fluid pressure in the scala tympani; bulges into the tympanic cavity



fluid contained within the membranous labyrinth



fluid contained within the bony labyrinth and bathing the membranous labyrinth

card image

no data


Saccule, Utricle

- sacs found within the vestibule

- sites of the maculae


Cochlear duct

contains the spiral organ


Semicircular ducts

positioned in all spatial planes


Basilar membrane

hair cells of the spiral organ rest on this membrane


Tectorial membrane

gelatinous membrane overlying the hair cells of the spiral organ



contains the crista ampullaris


Otoliths, Saccule, Utricle, Vestibular nerve

function in static equilibrium


Ampulla, Ampullary cupula, Semicircular ducts, Vestibular nerve

function in dynamic equilibrium


Cochlear nerve

carries auditory information to the brain


Ampullary cupula

gelatinous cap overlying hair cells of the crista ampullaris



grains of calcium carbonate in the maculae


Trace the pathway through which vibrations are transmitted to stimulate the hair cells in the spiral organ.

Tympanic membrane > malleus > incus > stapes > oval window > perilymph > cochlear duct > endolymph > basilar membrane with hair cells


Describe how sounds of different frequency (pitch) are differentiated in the cochlea.

The frequency determined by the length and tension of the basilar membrane fibers. High pitch sounds = oval window. low pitch = basilar membrane near apex of cochlea.


Explain the role of the endolymph of the semicircular canals in activating the receptors during angular motion.

When angular motion occurs in one direction, the endolymph in a semicircular canal lags behind, pushing the cupula in a direction opposite to that of the angular motion. Depending on the ear, this depolarizes or hyperpolarizes the hair cells, resulting in enhanced or reduced impulses to the brain.


Explain the role of the otoliths in perception of static equilibrium (head position).

When the head moves, otoliths move in response to variation in gravitational pull. As the deflect different hair cells, they hyper polarize or depolarize hair cells and modify the rate of impulse transmission along vestibular nerve.


Conduction deafness

- can result from the fusion of the ossicles

- can result from impacted cerumen or a perforated eardrum


Sensorineural deafness

- can result from a lesion on the cochlear nerve

- sound heard in one ear but not in the other during bone and air conduction

- can result from a blood clot in the primary auditory cortex


Conduction deafness and Sensorineural deafness

- can result from otitis media


The Rinne test evaluates an individual's ability to hear sounds conducted by air or bone. Which is more indicative of normal hearing?

Air-conducted sound



involuntary rolling of the eyes in any direction or the trailing of the eyes slowly in one direction, followed by rapid eye movement in the opposite direction



sensation of dizziness and rotational movement when such movement is not occurring or has ceased


The Barany test investigated the effect that rotatory acceleration had on the semicircular canals. Explain why the subject still had the sensation of rotation immediately after being stopped.

subject has vertigo


What is the usual reason for conduction the Romberg test?

to determine if impulses are being transmitted up the spinal cord to the brain properly


Wast he degree of sway greater with the eyes open or closed? why?

closed; you lose visual reference points


Normal balance, or equilibrium, depends on input from a number of sensory receptors. Name them.

vestibular receptors, visual receptors, somatic receptors


What effect does alcohol consumption have on balance and equilibrium? Explain.

alcohol depresses the neurons and enhances the inhibition of coordination and causes a loss of equilibrium reflexes

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