Auditory Pathways Flashcards
How are frequency and amplitude measured?
Frequency - Hertz = pitch
Amplitude - decibels = loudness
What is the logic for why the pressure calculation for decibels is multiplied by 20 rather than 10?
decibel scale multiplication by 10 is based on the intensity of sound. Intensity = Pressure^2. Since you take the log of pressure^2, 2log Pressure is the same as this. 102 = 20. This is all based on the intensity or pressure of a standard sound which is the threshold of human hearing
What is the range of human hearing, and where is it most sensitive?
20-20,000 Hz, most sensitive 1,000-3,000 Hz. Outside of this range, you need more than 0 dB of intensity in order to hear. Your hearing degenerates (curve moves above 0 dB in optimal range) as you age.
What device is used to detect an individual’s threshold of hearing?
Audiometer
How loud does something have to be before you can feel it?
140 dB
What is the approximate natural frequency of the external ear?
3000 Hz
What is the function of the middle ear ossicles? What frequencies is it good at?
Impedance match the air (tympanic membrane) with the inner ear (oval window). Since the foot of the stapes is so much small than the energy being taken on the tympanic membrane, 22 times as much pressure is put on the oval window than the tympanic membrane.
Its resonant frequency is ~ 1400 Hz, and is best in the range of 600-6000 Hz.
What muscles are involved in the attuenation reflex?
Tensor tympani - insertion to malleus, via V3
Stapedius - insertion to stapes, via 7
What two compartments border the Organ of Corti? What fills them?
Scala media - between Scala tympani + scala vestibuli. Filled with endolymph - high K+ / low Na+
Scala tympani - below basilar membrane - filled with perilymph - high Na+, low K+.
What compartment is directly adjacent to the oval and round windows?
Oval - scala vestibuli, separated from scala media via Reissner’s membrane.
Round - Scala tympani.
Scala tympani + scala vestibuli are continous at the helicotrema, at the apex of the modiolus (the bone).
Where are high and low frequencies carried by the basilar membrane, and how does this excite hairs?
High: Near the base
Low: near the apex
excites hairs by moving basilar membrane and depolarizing towards kinocilium of the inner hair cells via pulling on the tectorial membrane.
What is the function of the inner hair cells vs outer hair cells and where do they synapse?
Inner hair cells: one row, involved in the main processing of sound
Outer hair cells: four rows, involved in the amplification of sound. They are separated by an arch of pilar cells.
They synapse on the peripheral processes of the cells of the spiral ganglion, releasing glutamate neurotransmitters. The central processes of these neurons form the cochlear nerve.
Where does CN8 enter the brain?
Cerebellopontine angle, which is between the medulla and the pons. Cochlear and vestibular nerves are so closely associated we call them one nerve.
Where are the cochlear nuclei located (cochlear nuclear complex)?
On the lateral surface of the inferior cerebellar peduncle, near cerebellopontine angle. This is between medulla and pons transition.
What happens to the cochlear nerve fibers which synapse in the cochlear nuclear complex?
Dorsal: axons cross midline and ascend the brain in the dorsal acoustic stria
Ventral: Axons cross midline as intermediate acoustic stria to ascending auditory pathways. Also gives axons to ventral acoustic stria to ascending auditory pathways, which gives collaterals.
