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The ability to detect and interpret sound waves
distance from the peak of one wave to thenext
number of complete wavelengths in a second (Hz);
-Short wavelengths have ___ frequencies perceived as high pitch or tone
-•Long wavelengths have __ frequencies perceived as a lower pitch.
pitch depends on ___
Intensity depends on ___
Timbre depends on ____
- –pinna(ear) and auditory canal
- separated from middle ear by tympanic membrane or ear drum
- •hammer, anvil and stirrup;
- •connect the eardrum to the oval window
eustachian tube: equalizes pressure between middle ear and atmospheric pressure
cochlea and vestibular system generates signals that travel to brain.
How do the hair cells of the basilar membrane interact with the tectorial mambrane
The stereocilia (hairs)from the hair cells of the basilar membrane make contact with the overlying tectorial membrane. These hairs are bent when the basilar membrane is deﬂected in relation to the stationary tectorial membrane by. This bending opens channels, leading to ion movements that result in a receptor potential.
What causes deflection of the basilar membrane?
fluid movement in the cochlea
The tectorial membrane
– a gel like structure that overlies the sensory inner hair cells and elecrtically-motile outer hair cells of the organ of corti
- tip of cochlea if stretched out
- transition between Scala vestibuli and scala tymponi
The Basilar Membrane
- - seperates the two liquid filled canals
- •Formed by thin elastic fibers tensed across the cochlear duct;
- •The fibers are short and closely packed in the basal region close to the stapes, and become longer and sparse towards the apex of the cochlea;
- -Ends in a foramen that joins the two portions of the spiral canal
What are the three cavities of the cochlea
- Scala tympani
- Scala media
- Scala vestibuli
- -Part of cochlea that connects to oval window
- -filled with perilymph
What is paralymph
- An extracellular fluid with an ionic composition comparable to that of plasma and cerebrospinal fluid rich in sodium
- -found in Scala tympani, and Scala vestibuli
- -outer layer of semi-circles
- -contains tectorial membrane and organ of corti
- -separated from the scala tympani by the basilar membrane
- -Seperated from Scala vestibuli by vestibular membrane
- -filled with endolymph
What is endolymph
- a unique extracellular fluid in which potassium, not sodium is depolarizing electrical current in the hair cells of the corti organ
- -found in Scala media
- -inside portion of semi circles
a continuation of the scala tympani at the helicotrema
Which is more positive electrically?
Perilymph or endolymph?
- the electrical potential of endolymph is 80-90 mv more positive than perilymph due to a higher concentration of K compared to Na
What happens when sound waves enter the outer ear?
1) tympanic membrane(ear drum) vibrates back and forth;
2)Ossicles transfer vibration to oval window–sends pressure waves through cochlea;
- 3)Waves travel from vestibular canal to tympanic canal and dissipate against round window or
- -vibrate basilar membrane causing auditory sensor reception
What are the two pathways that Fluid movement within the perilymph set up by vibration of the oval window follow?
- 1) Through the Scala vestibuli, around the helicotrema and through the scala tympani, causing the round window to vibrate.
- - this pathway just dissipates sound energy
- 2)A shortcut from the scala vestibuli through the basilar membrane to the scala tympani.
- -This pathway vibrates the basilar membrane, displacing the organ of corti bending hairs triggering activation of the receptors for sound in the tectorial membrane
The narrow, stiff end of the basilar membrane nearest the oval window vibrates best with ___ ____ pitches
•The wide, ﬂexible end of the basilar membrane near the helicotrema vibrates best with ___ ___ pitches.
The Organ of Corti
- •A highly specialized structures that respond to fluid-borne vibrations in the cochlea with a shearing vector in the cochlear hair cells;
- •Convert pressure waves into action potentials;
The organ of corti contains between ___and____ auditory nerve receptors with its own hair cell;
15,000 and 20,000
How are Mechanical vibrations transduced into electrical signals by the organ of Corti?
- –The shear on the hairs opens ion channels that are permeable to potassium and calcium;
- –Cell plasma membrane depolarize with activation of voltage-dependent calcium channels at the synaptic basolateral pole of the cells which triggers vesicle exocytosis and liberation of glutamate to the synaptic cleft
What neurotransmitter is associated with the transduction of sound waves into electrical signals?
Where do electric signals from the organ of corti go and how?
–The electrical signal travel to the auditory cortex in the brain via ganglion neurons.
Frequency of action potentials in organ of corti determined by:
up-and-down vibration of basilar membrane
How does the shearing the hairs of the organ of corti effect signaling?
- -Hairs bending in one direction sends an action potential
- -Bending in the other direction shuts off neurotransmitter release
Ability to sense the position, orientation, and movement of the body
–Small round structures made of hair cells and statoliths (dense object), used by many aquatic invertebrates to send positional information
- -Small particles, composed of a combination of a gelatinous matrix and calcium carbonate in the viscous fluid of the saccule and utricle
- -The inertia of these small particles stimulate hair cells when the head moves
Vestibular system in vertebrates
- –Located in inner ear next to cochlea;
- –Utricle and saccule detect linear movements of the head
- –3 Semicircular canals detect motion in 3 dimensions
- (superior, posterior, horizontal)
3 Semi circle canals
Inner portion is filled with ___
outer layer is filled with ___
-3 endolymph/perilymph filled canal loops in the ear that detect 3 dimension movement of the head
How do the fluid filled canals detect 3 dimensional movement?
- •Each canal oriented in one of the three planes
- •When head moves endolymph in the canal shifts in the opposite direction, pushing on the copula and bending hair cells
-otolith/endolymph filled sacks that detect horizontal movement.
-otolith/endolymph filled sacks that detect vertical acceleration.
- -found within the ampula at the end of each semicircular canal
- -contains many receptor cells connected to vestibular nerve
- -receptor cell unit contains two types of hairs 1 kinocilium and 40-70 stereocilia
longer hair sensor, one per 40-70 stereocilia in cupula
How do the hair cells function to send electric signal in the cupula?
- -When the 40-70 stereocilia move towards the kinocilium the hair cell depolarizes
- -when they move away the cell is hyperpolarized
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