Exercise 25 Special Senses: Hearing and Equilibrium

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

Oval window

Fluid contained within the bony labyrinth and bathing the membranous labyrinth.

Perilymph

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

Round window

Sacs found within the vestibule and sites of the maculae.

Saccule and Utricle

Contain receptors for the sense of balance.

Semicircular canals, Vestibule

Positioned in all spatial planes.

Semicircular ducts

Define vertigo.

Sensation of dizziness and rotational movement when such movement is not occurring.

During the sound localization experiment in which the sound was least easily located. How can this phenomenon be explained?

The usual cues that allow sound to be localized (slight differences in loudness in the two ears and in the time the sound reaches each ear) are missing.

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 otitis media - Can result from a blood clot in the primary auditory cortex

Conduction deafness

- Can result from the fusion of the ossicles - Can result from otitis media - Can result from impacted cerumen or a perforated eardrum

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

Contains the crista ampullaris.

Ampulla

Function in dynamic equilibrium.

Ampulla, Ampullary cupola, Semicircular ducts, and Vestibular nerve

Gelatinous cap overlying hair cells of the crista ampullaris

Ampullary cupula

Structure composing the external ear.

Auricle (pinna), External acoustic meatus, and Tympanic membrane

Hair cells of spiral organ rest on this membrane.

Basilar membrane

How do sound waves reach the cochlea when conduction deafness is present?

By vibration through bones of the skull.

Was the degree of sway greater with the eyes open or closed? Why?

Closed. Visual cues (input) were lacking.

Structures composing the internal ear.

Cochlea, Semicircular canals, and Vestibule

Contains the spiral organ.

Cochlear duct

Carries auditory information to the brain.

Cochlear nerve

What factors might account for a difference in the acuity of the two ears?

Earwax, middle/external ear infection, cochlear nerve damage, etc.—anything that affects sound conduction or nervous system structures associated with hearing.

Fluid contained within the membranous labyrinth.

Endolymph

When the tuning fork handle was pressed to your forehead during the Weber test, where did the sound seem to originate?

From the ears

Where did it seem to originate when one ear was plugged with cotton?

From the plugged ear

In the frequency experiment in tuning fork was the most difficult to hear. What conclusion can you draw?

High-frequency sounds are heard less well at low intensity.

Collectively called the ossicles.

Incus (anvil), Malleus (hammer), and Stapes (stirrup)

Define nystagmus

Involuntary rolling or trailing of the eyes in one direction and then rapid movement in the opposite direction.

Grains of calcium carbonate in the maculae

Otoliths

Function in static equilibrium.

Otoliths, Saccule, Utricle, and Vestibular nerve

Involved in equalizing the pressure in the middle ear with atmospheric pressure.

Pharyngotympanic (auditory) tube

Passage between the throat and the tympanic cavity.

Pharyngotympanic (auditory) tube

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

Proprioceptors of the muscles and tendons, vestibular apparatus of the ears, retina of the eye (photoreceptors)

Gelatinous membrane overlying the hair cells of the spiral organ.

Tectorial membrane

Explain why the subject still had the sensation of rotation immediately after being stopped.

The fluids of the inner ear had not yet stopped moving.

What is the usual reason for conducting the Romberg test?

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

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

Tympanic membrane

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

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