Auditory system Flashcards
Define pitch, timbre, amplitude, intensity. Give the name of scale used to measure loudness
- Pitch: perception of frequency
- Timbre: what distinguishes two sounds at the same frequency and intensity
- Amplitude = intensity, perceived as loudness
- Intensity = how many joules per second pass through one square meter (j/sm2 or W/m2)
- Decibel range = log scale of loudness
Describe the structure of the cochlea
- Hollow tube in bone, curled into spiral
- Divided longitudinally into 3 compartments, separated by 2 membranes
- Sound wave causes vestibular (Reissner’s) and basilar membranes to vibrate
- Hair cells are attached to basilar membrane pic
LO 46 Describe the Mechanisms of amplification
Conduction through middle ear amplifies sound by 30dB Achieved by lever system of articulated ossicles and ratio of area of tympanic membrane to oval window Protective mechanisms Reflex contraction of tensor tympani and stapedius muscles reduces amplitude of vibrations passing through ossicles Protects against natural sounds but maybe not against man-made sounds Auditory tube allows equilibration of air pressure on either side of tympanic membrane
Describe the pathway of auditory transduction
- Sound waves pass through external auditory canal to stimulate tympanic membrane
- Vibration stimulates vibration of auditory ossicles (3bones: malleus, incus, stapes)
- Ossicles transmit vibration of tympanic membrane to cochlear
- In cochlear: motion of stapes generates a difference in pressure between the two liquid-filled chambers of the cochlea, which cause vibration of the basilar membrane where hair cells lie. Organ of corti: basilar and tectorial membranes, hair cells and supporting cells
- Stimulation of hair cells sends signal to brain via cochlear nerve (hair cells synapse with sensory neurons in cochlear ganglion) -> tonotopic map
Describe the transduction mechanism
- Basilar membrane vibrates in response to sound
- Upward movement displaces stereocilia away from modiolus → K+ channels open → K+ enters from endolymph → hair cell depolarises
- Downward movement displaces stereocilia towards modiolus → K+ channels close → hair cell hyperpolarises
- Highly sensitive – response to threshold sound requires 0.3 nm deflection
- Depolarisation opens Ca++ channels in body of hair cell
- Glutamate released from base depolarises axon of spiral ganglion cell → action potential
Name the 2 types of hair cells
Inner hair cells:
- afferent projections (sensory axons that carry signals from the cochlea to the brain)
- SENSORY TRANSDUCTION
Outer hair cells:
- efferent projections (from brain to cochlea)
- ACTIVE PROCESS
Basilar membrane and hair cells. Describe their role
- vibrates at dif positions along its length in response to different frequencies
- breaks complex sounds down by distributing E of each component frequency along its length sensory receptors along its length: hair cells bending of stereocilila (cluster of modified microvilli that make up the hair bundle)
- produces electrical signal that goes to brain (MT=mechano-transduction: mechanical stimuli converted to electrical)
- stereocila connnected by tip links (filamentous ligaments): opening of ion channels due stretching of tip links causes response
The active process. Give the 4 aspects.
- amplification
- frequency tuning
- compressive nonlinearity
- spontaneous otoacoustic emission
details?, graphs on slide
What is impedance? What does it depend on?
- Impedance: measures the reluctance of a system in receiving E from source -> depends on mechanical properties, determines resonant frequency
- Resonant frequency: the f at which the impedance of a system in minimal
What is conductive hearing loss? Give its causes
sound waves cannot be transmited to cochlear
Causes:
- wax
- otitis media
- otosclerosis (abnormal growth of bone) of ossicles
- perforated tympanic membrane
- congenital malformations
- fluid accumulation in children
What is sensorineural hearing loss? Give its causes.
Malfunctioning of auditory pathway in brain. Demyelination or blast injuries (cause disruption in balance between inhibition and excitation SOC)
Causes:
- loud boises
- headphones
- ageing
- acoustic neuroma
Give a solution for hearing loss
Hearing loss due loss of hair cells (dont regenerate).
Solution: bypass dead cells and stimulate nerve fibre directly -> cochlear implants
Describe electromotility in relation to the active process
Electromotility: cell body of outer hair cels shortens and elongates when their internal voltage is changed, due to reorientation of protein plastin
Auditory Pathways. Explain tonotopic arrangement and spectral cues.
TONOTOPIC ARRANGEMENT: (low frequencies ventrally, high frequencies dorsally)
Ventral and dorsal Cochlear Nucleus
Spectral Cues: ears detect and affect differently sounds coming from different directions due to their asymmetrical plane
Superior Olivary Complex. Give its role and the 2 subdivisions.
Compares bilateral activity of cochlear nuclei
- Medial Superior olive: inter-aural time difference is computed (delay lines)
- Lateral superior olive: detects differences in intensity between two ears. interaural level difference is computed to localise sounds in horizontal plane.
Excitation must arrive at same time as inhibition.
- Inhibitory: contralateral (large axons with large synapses, Large catalyses of Held)
- Excitatory: ipsilateral (smaller axons, conduct more slowly) SOC: sends feedback to hair cells to balance responses.
