Quarter 4 neuroscience Auditory function

- mechanical shear forces produced by sound waves

- convert the energy of sound waves into electrical energy (transduction) and convey the resultant AP to the auditory cortex

20 to 20,000 hz

1000-4000 hz

200-4500 (hz)

loudness

- characterized by a single sinusoidal wave form,
- discrete frequency

- complex tones characterized by a primary frequency with one or more harmonic frequencies

- give uniquenss to a given sound

many nonharmonic frequencies occuring simultaneously

- log [intensity of sound/intensity of reference sound] or bel

10 times a just noticeable sound

- funnels sound into the auditory canal and helps in determining sound direction

- 3500 which minimizes the attenuation of sound in the normal human voice

- separates the middle ear from teh external environment
- vibrates in response to incoming sound waves

- malleus
- incus
- stapes

hammer

anvil

stirrups

- transmit sound waves from the eardrum to the oval window

matches acoustical impedance of the air to the liquid filled inner cavity increasing sound pressure reaching the oval window

- connects the middle ear to teh pharynx
- allows the air pressure within the middle ear to equibilrate with the atmosphere

deformation of the tympanic membrane

regulate the amount of sound transmitted to the inner ear

- tensor tympani
- stapedius

pulls the stapes away from the oval window

- controls tension on the tympanic membrane
- enhances sound transmission up to 15 dB at 1000-2000 Hz

tensor tympani and stapedius contract in response to loud sounds and other stimuli.

- protecting the ossicles from jostling
- filtering self- initated sounds
- masking low frequancy sounds

- generate rocking and twisting motion as well as back-and -forth motion, dissipating energy inherent in loud

transduction of sound waves into electrical potential

- oval window
- round window
- helicotrema

at the base of the cochlea in the upper chamber (scala vestibuli)

- at the base of the cochlea in the lower chamber (scala tympani)

- space where the scale vesti buli and tympani converge, at the apex of the cochlea

- contacts oval window and connects with the scala tympani at the helicotrema

- perilymph

- low k+ high na+

- contacts the round windo and connects with the scala vestibuli at helicotrema

lies between the scala vestibuli and the scala tympani

blindly near the apex of the cochlea

- endolymph (high k+, low Na+ similar to IC fluid)

perilymph (low K+, high Na+)

- scala vestibuli
- scala tympani
- scala media

- cochlear duct

reissner's membrane
basilar membrane

separates scala media from the scala vestibuli

- separates scala media from scala tympani

- organ of corti

on the basilar membrane within the scala media

- excitable cells embedded in a matrix of other supporting cells and collagen
- 3 rows of outer hair cells, many cells convergent with one afferent
- one row of inner hair cells, no convergence

- overlies the organ of corti

- stereocilia of hair cells embedded in this structure and the sensory hair cells

- impinge on the tympanic membrane, the tympanum oscillates and they are transmitted through the ossicles to the stapes which oscillates and vibrates the oval window and energy is transmitted to the fluids of the ear

- movement in the scala media and the basilar membrane,
- organ of corti moves
- tectorial membrane does not vibrate

- central process of the cochlea

- creates a shearing force on sterocilia of the hair cells which opens and closes the mechanically sensitive sodium channels

- depolarization increases release
- hyperpolarizaion decrease
- NT is excitatory
- released in oscillating fashion

at the base of the cochlea

toward the apex

- refines the signal by an excited neuron to reduce the activity of neighboring neurons, causing the sensation of a single tone

- produces more than one peak waveform, and a composite sound is sensed

tonotropically on their way to the cortex allowing the frequency response of the organ of corti to be preserved at higher neural levels

it increases also

time

intensity

- 90 percent from inner hair cells (discrete innervation)
- 10 percent from outher hair cells (diffuse innervation

- relay, signal refinement, improve signal to noise ratio

- the cochlear nuclei

toward the trapezoid body and interneurons to the superior olivary complexes on both sides of the medulla

- contain binaural cells which recieve auditory input from both ears to sense direction

lateral lemniscus

relay

to the inferiro colliculus which recieves binaural input

signal routing and dampining

inferior colliculus

preception of sounds
- axons from the geniculate nucleus project to the primary auditory cortex located in the superior temporal gyrus

- do not disrupt the preception of sound frequency but do not affect localization

external or middle ear deficit impede the transmission of the sound waves to the inner ear

often normal

- cannot hear a tuning fork held next to ear
- can hear a tuning fork when the stem is placed against the temporal bond

- otosclerosis
- rigidity of the ossicular chain
- tympanic membrane deficits
- blocked auditory canal

- stapes becomes locked in place due to excessive bony growth

reduces the transmission of sound vibrations to the oval window

rupture, thickening

- deficits in the hair cells, the afferent pathways or the central auditory areas prevent sound perception

- cannont hear a tuning fork held next to ear
- cannont hear tuning fork when the stem is placed on temporal bone

- prolonged exposure to loud sounds
- tinnitis
- drug toxicity

the spontaneous discharge of damaged hair cells