Physiology-Auditory System Flashcards
Wavelength
Peak to peak of sound wave
Frequency (pitch)
Wavelengths per unit time
Amplitude (loudness)
Difference between peak pressure of sound wave and mean pressure.
Decibel scale
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What decibel increase correlates with a 10 fold increase in absolute sound pressure amplitude?
20 dB
Timbre
Shape of waveform (note on a trumpet vs. note on a flute).
What is the range of hearing in humans?
20 Hz - 20 kHz
Minimum sound pressure level needed for perception of the sound.
Threshold, note that the decibel level required to hear the noise varies greatly with frequency.
What structure helps you determine whether a sound is coming from above or below you?
Auricle. It filters and amplifies certain frequencies based on the location they come from. The brain then integrates these frequencies and can determine where the sound came from.
What structure helps you conduct sound waves to the tympanic membrane?
External auditory meatus. It selectively amplifies sounds in the 2-5 kHz range, which is why we are most sensitive to sounds in that frequency range.
How does the middle ear amplify noises that bounce off the tympanic membrane?
The tympanic membrane is 21x larger than the oval window. The malleus is 1.3x longer than the incus. This results in a theoretical amplification of 25 dB by the middle ear.
What muscle adjust as you prepare to speak? What bones are they attached to and what are they innervated by?
Malleus = tensor tympani, CN V. Stapes = stapedius, CN VII. The move the ear to decrease amplifications of sounds > 80 dB, protecting you from damaging your own hearing.
How does the sound transmitted by the cochlear duct get transmitted to the CNS?
Sound wave -> Movement of basilar membrane -> Hair cells move -> Increase neurotransmitter release by hair cells -> Cochlear nerve action potential
How does the pressure wave generated by the stapes travel? How does this affect hearing?
It propagates through the oval window, through the scala vestibuli, around the helicotrema, through the scala tympani and relieved at the round window VERY RAPIDLY. This rapid pressure disturbance sets up a traveling wave along the basilar membrane.
How does stiffness of the basilar membrane affect amplitude of sound waves?
At the base, near the round window, it is stiff and amplitude is very low. At the apex of the basilar membrane, it is more floppy and can be displaced more.
What frequencies cause maximum displacement of the basilar membrane?
Low.
How does the CNS determine the auditory frequency of a sound?
Where it came from on the basilar membrane. High frequency sounds will be transmitted via hair cell afferent fibers closer to the base of the basilar membrane. Low frequency sounds will be transmitted via hair cell afferent fibers closer to the apex of the basilar membrane.
How does the CNS differentiate low frequency sounds that are below 500Hz?
At lower frequencies the entire apex is oscillating according the frequency of the sound. The CNS can interpret the sound by analyzing the gaps between nerve firings as the entire apex oscillates. This is called the Temporal (volley) theory.
How does sound signal transduction take place to the primary auditory cortex?
Spiral ganglion neurons -> CN VIII (Cochlear) -> Cerebellopontine angle -> Synapse in dorsal & ventral cochlear nuclei of medulla -> Secondary axons cross through the pontine tegmentum and become the lateral lemniscus -> Inferior colliculus -> Brachium of the inferior colliculus -> Medial geniculate body of thalamus -> Internal capsule -> Transverse Gyri of Heschl (primary auditory cortex)
How does your brain know if a sound is coming from in front of you or from the side?
A number of fibers from the cochlear nuclei of the medulla land in the superior olivary complex where they synapse. Neurons in this complex are sensitive to time of arrival of the action potential and tell you whether it was in front or to the sides. Axons from the olivary nucleus then go up the lateral lemniscus.
What pathway helps us hear people in the presence of background noise?
Descending auditory pathway. It follows the same path as the ascending pathway, except it stops at the olivary nucleus. Olivocochlear fibers are sent from the olivary nucleus to the inner ear to decrease transmission of irrelevant frequencies.
How do you distinguish between conductive or sensorineural loss?
Weber’s Test: The patient will hear the sound louder on the bad side if they have unilateral conductive loss. If they have unilateral sensorineural loss, they will hear the sound better in the good ear. Rhinne Test: sound is louder when on the mastoid process if the patient has unilateral conductive loss. Sound is louder by air conduction if the patient has unilateral sensorineural loss.
How does audiometry work?
You measure how many more decibels are required to hear specific frequencies compared to normal hearing.
What type of hearing loss is this?
Conductive, hearing loss is uniform across the board.
What type of hearing loss is this?
Age-related: hearing loss is happening first at higher frequencies.
What type of hearing loss is this?
Noise traum: shooter’s notch at 4kHz
