Physiology of Hearing and Equilibrium- Physio- Gonsalves

Sound

Vibration of air molecules traveling in waves, need a medium in order to have a particular wave.

Compression Waves

Sound travels in compression waves through a medium

Solid

Fastest medium for sound to travel through

Liquid

Medium for sound to travel through, slower than solid

Gas

Slowest medium for sound to travel through

Compressions

High pressure areas in a sound wave

Rarefactions

Low pressure areas in a sound wave

Sine Wave

Graphic representation of areas of compression and rarefaction in a sound wave

Wavelength

Distance between two areas of compression in a sound wave

Frequency

Number of waves that pass a given point in one second

Short Wavelength

High frequency, high pitched tones

Long Wavelength

Low frequency, low pitched tones

Human Frequency Range

20Hz - 20,000Hz (2-3 Hz distinction between waves)

Amplitude

Intensity of energy in a sound wave, signified by height of sine wave

Loudness

Subjective interpretation of the intensity of a sound

Decibel

Logarithmic scale to measure the intensity of sound waves

Threshold for Audibility

0 dB, barely audible

Perceived Loudness

Increase in amplitude corresponds to increase in loudness

Transmission of sound to the inner ear

air -->

external auditory canal -->

tympanic membrane (ear drum) -->

ossicles (malleus, incus, stapes.) -->

oval window of cochlea -->

vibration of cochlear fluid -->

basilar membrane of cochlea

Cochlea

Part of the inner ear responsible for sound vibration

resonance of the basilar membrane

1. Vibration of oval window- perilymph vibration

2. for 20-20,000 Hz only, vibration of vestibular mambrane

3. vestibular membrane vibration- endolymph vibration

4. endolymph vibration- vibration of basilar membrane

5. basilar membrane fibers of different lengths, thickness and tension like strings of a piano.

Basilar Membrane

Vibrates in response to cochlear fluid vibration

Resonance

Different fibers of the basilar membrane have different natural frequencies. The sound waves absorbed have the exact right energy.

Pitch

specific parts of basilar membrane vibrate only at specific frequency

Hair Cells

Rest on the basilar membrane, respond to vibration

What makes up the organ of corti?

basilar membrane, hair cells, and tectorial membrane

cochlear hair cells

rest on the basilar membrane, contain "stereocilia" which project into the "tectorial membrane" just above

Excitation of the Hair Cells of the Organ of Corti

Basilar vibration- hair cell vibration (moves left or right)

Hair cell vibration (bending of hair) - opens or closes ion channels

depolarization/hyperpolarization- cochlear nerve

cochlear nerve impulses- brain

transduction

Anatomical pathway to the brain

cochlear nerve

spiral ganglion

cochlear nuclei

superior olivary nucleus

lateral lemniscal tract

inferior colliculus

medial geniculate body of thalamus

auditory cortex

A physical vibration is changed into a an electrical signal which turns into a chemical signal and back to electrical

transduction

Organ of Corti

Contains cochlear hair cells

Anatomical Pathway to the Brain

Cochlear nerve -> spiral ganglion -> cochlear nuclei -> superior olivary nucleus -> lateral lemniscal tract -> inferior colliculus -> medial geniculate body of thalamus -> auditory cortex

Perceiving Pitch

Location of vibration on the basilar membrane, different frequencies cause different excitation of the basilar membrane

Perceiving Differences in Loudness

Amplitude increases, more hair cells of the basilar membrane (with the same pitch) are activated

Localizing Source of Sound

Superior olivary nucleus determines relative intensity and timing. First point where sound from both ears comes together.

Conduction Deafness

Disruption in sound vibrations to the basilar membrane

Relative intensity

the amplitude of sound waves hitting the different ears

Relative timing

the difference in timing in which a sound reaches both ears

Sensorineural Deafness

Disruption anywherein pathway from hair cells to the auditory cortex

Reasons for conduction deafness

blocked auditory canal

perforated tympanic membrane

otitis media- middle ear infection/inflammation

otosclerosis- hardening of the earbone joints.

Tinnitus

Chronic perception of clicking or ringing

Reasons for senorineural deafness

1. loss of hair cells (explosion, chronic loudness)

2. damage to vestibulocochlear nerve

3. damage to nuclei/tracts to the cortex

Menierre's Syndrome

effects both hearing and balance; results in tinnitus, vertigo, and interspersed nausea and vomiting

Causes of tinnitus

sudden blow to tympanic membrane

gradual deterioration of afferents in cochlear nerve

Vestibular Apparatus

Responsible for equilibrium and balance

Maculae

patch of "supporting cells" and "hair cells" along the utricles and saccules

Causes and treatment for Menierre's syndrome

1. too much endolymph beneath basilar membrane

Symptoms can be treated somewhat with drugs. Endolymph may be drained periodically. Hearing loss is progressive.

Vestibule

bony cavity of the inner ear between the cochlea and the semicircular canals

saccule and utricle

smaller sacs housed within the vestibule

Otolithic Membrane

Jelly-like sheet that abuts the stereocilia of the hair cells in the maculae. Has films which give it inertia so it can detect acceleration.

Semicircular Canals

three bony hula hoop extensions of the vestibule in three different planes

vestibular hair cells

Located in semicircular canals, found in inner ear

-Detect acceleration and position relative to gravity. Bend.

Crista Ampullaris (at the base of the semicircular canals)

like maculae, contains hair cells that respond to flow of endolymph in the canals

otoliths

"ear stones" that rest on top of the otolithic membrane

In horizontal acceleration

maculae of UTRICLE is in the horizontal plane; hairs bend when motion is FORWARD/BACKWARD

In vertical acceleration

maculae of SACCULE is in the vertical plane; hairs bend when motion is UP/DOWN

Vestibular Nystagmus

Movement of eyes to remain fixed on object during rotational movement (when on merry go round)

Equilibrium Pathway

Activated hair cells of crista ampularis -> afferent axon fibers -> vestibular nuclear complex or cerebellum

cupula

like otolith membrane, gelatinous cap into which hair cells project

Equilibrium

angular+horizontal+vertical

In vertical and horizontal acceleration the ___________ is moving

otolithic membrane

In angular acceleration the ___________ is moving because of fluid pushing against it

cupula

Problems with Equilibrium

Dizziness, nausea, imbalance, vomiting

Vertigo

false feeling of gravity or motion

Motion Sickness

Conflict between visual/somatic inputs and vestibular apparatus

Change in angular (rotational) acceleration is the

movement of the head in a non-linear (circular or angular) direction is monitored by the semicircular canals.

Vestibular nuclei

also receive input from eyes and somatic proprioceptors; coordinates information to help control motion of eyes, neck, limbs

cerebellum

also receives input from eyes and somatic proprioceptors; coordinates information to help regulate head position, posture, and balance.