Auditory System

The human pain threshold is approximately 10^6 10^3 10^9( 10^6, 10^3, 10^9 ) times higher than the hearing threshold.

The speed of sound increases decreases( increases, decreases ) with the density of the medium.

Humans have their highest sensitivity between 1 2 10 20( 1, 2, 10, 20 ) and 4 40 10 20( 4, 40, 10, 20 ) kHz Hz( kHz, Hz ).

Human speech is roughly between 1 2 10 20( 1, 2, 10, 20 ) and 2 20 40 4( 2, 20, 40, 4 ) kHz Hz( kHz, Hz ).

Pinna and ear canal amplify frequencies between 2 and 4 kHz 1 and 4 kHz 8 and 10 kHz 2 and 8 kHz( 2 and 4 kHz, 1 and 4 kHz, 8 and 10 kHz, 2 and 8 kHz ) by a factor of 8 4 2 16( 8, 4, 2, 16 ).

This is not is( is not, is ) uniformly effective for every direction.

Cell types of the cochlear nucleus:

Bushy Pyramidal Held( Bushy, Pyramidal, Held ) cells receive input via large excitatory inhibitory( excitatory, inhibitory ) Endbulbs of Held Calyx of Held( Endbulbs of Held, Calyx of Held ) and send output to the superior olivary nucleus inferior colliculus lateral lemniscus( superior olivary nucleus, inferior colliculus, lateral lemniscus ) via large synapses, called Calyx of Held Endbulbs of Held( Calyx of Held, Endbulbs of Held ).

Bushy cells have the largest synapses in the brain, which leads to great poor( great, poor ) temporal precision and an exact imprecise( exact, imprecise ) resolution (1 spike for 1 spike).

Sound localization:

There is strong evidence for the Jeffress Model for ITD processing in birds reptils mammals fish( birds, reptils, mammals, fish ).

In mammals it is called into question, e.g. by the fact that the MSO receives also inhibitory input the LSO receives also inhibitory input the MSO is not capable of summation the LSO is not capable of summation( the MSO receives also inhibitory input, the LSO receives also inhibitory input, the MSO is not capable of summation, the LSO is not capable of summation ).

Auditory belt areas (including secondary auditory cortex A2) are less also( less, also ) precise in their tonotopic organization.

They process combinations of isolated( combinations of, isolated ) frequencies and temporal sequences of sound.

A2 includes Wernicke's area Broca's area( Wernicke's area, Broca's area ).

During development the synaptic density peaks at 2-4 1-2 4-6( 2-4, 1-2, 4-6 ) years.
After that the brain needs to specialize its functions.

In juveniles synaptic potentials have a longer shorter( longer, shorter ) duration and synaptic plasticity is higher lower( higher, lower ).

Continuous noise input during the critical period of development result in a disrupted better( disrupted, better ) tonotopic organization and a degraded frequency response selectivity amplitude response selectivity ILD detection ITD detection( frequency response selectivity, amplitude response selectivity, ILD detection, ITD detection ) for neurons in the adult auditory cortex.

Early hearing loss leads to

(1) Delayed Premature( Delayed, Premature ) development with synaptic overshoot undershoot( overshoot, undershoot )
(2) Increased Less( Increased, Less ) elimination of synaptic function

The ratio of tympanum vs. stapes malleus incus( stapes, malleus, incus ) foot plate is 17 20 13( 17, 20, 13 ):1.

The leverage effect is 1.3 3.1 1.7( 1.3, 3.1, 1.7 ).

The cochlea has 2.5 2 3 3.5( 2.5, 2, 3, 3.5 ) coils and its length can vary between 28 and 41 30 and 45 15 and 38( 28 and 41, 30 and 45, 15 and 38 ) mm.

The hair cells are logarithmically exponentially linearly( logarithmically, exponentially, linearly ) distributed on the basilar tectorial( basilar, tectorial ) membrane. More hair cells are located towards the apex base( apex, base ) where low high( low, high ) frequencies are coded.

Inner hair cells contain stretch-activated K+ Na+ Ca2+( K+, Na+, Ca2+ ) channels. Upon depolarization voltage-gated Ca2+ K+ Na+( Ca2+, K+, Na+ ) channels open and lead to the release of glutamate dopamine glycine GABA( glutamate, dopamine, glycine, GABA ).