phys- ear exam 2

Alternate Regions of Compression & Rarefaction of Air Molecules

–Identification of the sounds (“what”)–Localization of the sounds (“where”)

• Traveling vibrations of air
• Consist of alternate regions of compression and rarefaction of air molecules

• 1. Pitch (tone) of sound
• –Depends on frequency of air waves
• –Higher pitch corresponds to greater frequency of vibration
• 2. Intensity (loudness)
• –Depends on amplitude of air waves–Measured in decibels
• Timbre (quality)
• –Determined by overtones, additional frequencies superimposed on the pitch

• Pinna: collects sound waves and channels them down the ear cana
• lThere are glands that produce cerumen (ear wax) lining the canal.
• Ear wax, along with fine hairs at the entrance to the canal, are protective mechanisms

The tympanic membrane vibrates when struck by sound waves

Alternating high & low pressures of the sound wave cause the tympanic membrane to bow inward & outward in sync with the frequency of the wave

the vibrations of the tympanic membrane into fluid movements in the inner ear

• middle ear transfers vibrations thru ossicles
• waves in cochlear fluid set basilar membrane in motion
• receptive hair cells are bent as basilar membrane is deflected up and down
• mechanical deformation of specific hair cells is transduced into neural signals that are transmitted to auditory cortex in temporal lobe of brain for sound perception

• Cochlea 
• »Contains receptors for conversion of sound waves into nerve impulses which makes hearing possible
• Vestibular apparatus
• »Necessary for sense of equilibrium

• Pea-sized & snail shaped
• Contains the organ of Corti
• A coiled tubular system
• Divided into 3 fluid-filled longitudinal compartments:         
•      1.Upper compartment is the scala vestibuli, follows inner contours of the coil
•      2.Middle compartment is the scala media (also called cochlear duct) 
•      3.Lower compartment is the scala tympani, follows the outer contours

• Perilymph: Fluid in the scala vestibuli and scala tympani
• The scala media has endolymph
• The fluid at the tip of the cochlear duct come together at the region of the helicotrema

middle ear cavity by the oval window

middle ear by the round window

top of the scala media, separating it from the scala vestibuli

floor of the scala media, separating it from the scala tympani

Basilar membrane

• the auditory hair cells, which are the receptors for sound
• auditory hair cell
• mechanoreceptors

fluid movement into neural signals

• Arranged in 4 parallel rows along the length of the basilar membrane
• the tectorial membrane, an awning type of membrane extending over the length of the Organ of Corti

• inward
• 1.Displacement of the round window (this is the imp one)
• 2.Deflection of the basilar membrane

• the narrow, stiff end of the basilar membrane nearest the oval window vibrates best with high-frequency pitches
• the wide, stiff end of the basilar membrane near the helicotrema vibrates best with low-frequency pitches
• Each region of the basilar membrane is linked to a specific region of the primary auditory cortex

• Inner cells transform the vibrations into action potentials, sending sensory information to the CNS
• The outer cells change length in response to changes in membrane potential (Electromotility). Enhances the response of the inner hair cells.

• 1.Sound waves enter external auditory meatus
• 2. Eardrum vibrates
• 3. Auditory ossicles (malleus, incus,stapes) amplify vibrations
• 4. Stapes hits oval window and transmits vibrations to cochlea
• 5. Organs of corti
• contain receptor cells (hair cells) that deform from vibrations
• 6. Impulses sent to the auditorynerve
• 7. Auditory cortex of the temporal lobe interprets sensory impulses

• 1. sound waves
• 2. vibration of tympanic membrane
• 3. vibration of middle ear
• 4. vibration of oval window
• 5. fluid movement within the cochlea -- (OR--> vibration of round window --> dissipation of energy (no sound perception))
• 6. vibration of basilar membrane
• 7. bending of hairs of inner receptor hair cells of organ of corti as basilar membrane movement displaces these hairs in relation to the overlying tectorial membrane which the hairs contact
• 8. grades potential changes (receptor potential) in receptor cells
• 9. changes in rate of action potentials generated in auditory nerve
• 10. propagation of AP to auditory cortex in temporal lobe of brain for sound perception

• stimulate the nerve directly
• A cochlear implant receives sound from the outside environment, processes it, and sends small electric currents near the auditory nerve.  
• These electric currents activate the nerve, which then sends a signal to the brain.
• The brain learns to recognize this signal and the person experiences this as "hearing". 
• The cochlear implant somewhat simulates natural hearing, where sound creates an electric current that stimulates the auditory nerve.
• The result is not the same as normal hearing.

• Semicircular canals
•     –Detect rotational acceleration or deceleration in any direction
• Utricle and saccule (the otolith organs
•     -Detect changes in rate of linear movement in any direction
•     –Provide information important for determining head position in relation to gravity

Detect rotational or angular acceleration or deceleration of the head.  They do not respond when head is motionless or moving at a constant speed.

• at right angles to each other
• in 3 different planes

an ampula

on a ridge in the ampulla.

the cupula, a gelatinous layer. This is the fluid layer.

fluid movement

it lags behind bc of inertia

• the fluid in the same plane as the head movement is in effect shifted in the opposite direction  from the movement.
• This causes the cupula to lean in the opposite direction of the head movement.
• The sensory hairs in the cupula also move in the direction opposite head movement.
• The endolymph will catch up if head movement continues at the same rate & in the same direction

One kinocilium and a tuft of stereocilia, arranged in rows of decreasing height

between the semicircular canals & the cochlea

he Tiny crystals of calcium carbonate that are suspended within the gelatinous fluid.

• the utricle hairs are vertical &
• the saccule hairs are oriented horizontally

mechanical deformation of hair cells by specific movement of fluid and related structures

vestibular nuclei in brain stem and to cerebellum for use in maintaining balance and posture, controlling eye movement, perceiving motion and orientation