Hearing Flashcards
Cycle
one complete oscillation of a wave
Frequency ( Hertz )
the number of cycle per seconds
ON AVRAGE : humans can hear between 20 and 20000 hertz
this is perceived as PITCH
Different sound sources can be perceived as having the same pitch but they differ in quality ( fundamental frequency )
Amplitude ( Decibels)
A measure of the intensity of the sound.
every increase of 3dB is equal to a doubling of sound intensity
intensity of 130 can induce pain . Exposure to sound above 120 db can lead to hear loss
Exposure to long 85 dB is dangerous o hearing
This is perceived as LOUDNESS
Sensorineural hearing loss
A Type of deafness caused by damage to hair cells within the inner ear
The outer ear : The pinna& auditory canal
the pinna which collects sounds from the environment & from below and above the vertical axis
the auditory canal : conducts sound energy from the outer to the middle ear
Middle ear : tympanic membrane ( eardrum) & ossicles
ossicles : malleus , incus and the stapes
Note : For sound waves to effectively go from air to water, they need to be amplified. The ossicles act as levers that transmit the pressure exerted on the tympanic membrane by the sound waves to the oval window, situated at the base of the cochlea, which has a much smaller surface area than the tympanic membrane. This results in the pressure at the oval window being much greater than it is at the tympanic membrane
inner ear : oval window and the cochlea
cochlea contains the semicircular canals which are important for balance
The cochlea is fluid filled and contains the receptors that are responsible for transducing energy from sound waves into electrical impulses, which ultimately leads to the perception of sound.
The pathway of sound
Once sound waves have made their way through the auditory canal, their energy causes the tympanic membrane to vibrate. This vibration is passed on to the ossicles, which in turn pass it on to the cochlea, where its fluid is set into motion and where specialized receptors are excited.
The Cochlea :
It coils around a bony pillar called the modiolus.
The cochlea has three chambers: scala timpani, scala media, and scala vestibuli.
Two types of fluids fill these chambers, endolymph and perilymph.
The scala tympani and scala vestibuli contain perilymph, whereas the scala media contains endolymph, which is rich in K+.
The organ of Corti
it is found in the Scala media .
it includes basilar membrane known as hair cells that is sandwich between the basilar membrane and the tectorial membrane
Basilar membrane
It is flexible and is set into a wavelike motion by the energy and pressure changes that create sound waves.
High-frequency sound waves create a ripple of waves that peak at the base of the basilar membrane, whereas low-frequency sounds create a ripple of waves that peak at the apex. Middle frequencies create ripples that peak around the center of the basilar membrane
Hair cells
Stereocilia are flexible. They easily bend toward or away from the kinocilium. Together, the stereocilia and kinocilium form the hair bundle.
hair cells send information toward the brain through afferent sensory neurons and receive information from the brain through efferent synapses.
The sound wave travel
When hair cells bend toward the kinocilium (positive direction), as occurs during the peak of a wave, the cell is depolarized and gives rise to action potentials in afferent fibers that bring auditory information to the brain. When the stereocilia bend away from the kinocilium (negative direction), as in a wave’s trough, the cell hyperpolarizes and action potentials generated by the hair cell cease to occur.
A neurotransmitter is released from the cell body itself onto the afferent fibers and receives information from the brain through efferent fibers that make direct contact with the cell body.
When the stereocilia bend in the positive direction, gates that permit the entry of K+, situated on each one of the stereocilia, are opened. This causes the cell to depolarize. Due to this depolarization, Ca2+ channels on the cell body open, permitting entry of Ca2+ into the cell. This in turn causes the synaptic vesicle to fuse with the membrane of the cell and to release neurotransmitter molecules onto afferent sensory neuron
( NOT NA2+)
Inner hair cells
relay information related to the frequency of sound waves to the brain, though afferent fibers,
95% of the auditory information relayed to the brain (cochlear nucleus) comes from inner hair cells.
This is because 90% of cells known as spiral ganglion cells innervate inner hair cells. In addition, each inner hair cell connects with several spiral ganglion cells, but each ganglion cell receives information from a single inner hair cell
outer hair cells
outer hair cells play a role in the amplification of sounds and receive information related to the location of sounds from the brain (superior olivary nucleus) through efferent fibers.
more than inner hair cells
