Neurobiology- Auditory System

What are the important features of sound?

frequency/pitch, duration, intensity, localization

What is sound?

pressure waves, alternating compression and rarefaction of air or water

How fast does sound travel in air?

350 m/sec

What are the three questions regarding how the nervous system detects sound?

How do neural systems detect sound? What are the reception and transduction mechanisms? What is the pathway of transmission to the CNS?

VIIIv

vestibular nerve

VIIIa

cochlear and auditory nerve

Duration

length of time

Intensity

magnitude of sound

frequency/pitch

number of signals per unit of time

Localization

where sound is coming from

List the components of the auditory pathway (nerves)

spiral ganglion > auditory nerve (primary afferent) > ventral or dorsal cochlear nucleus > superior olive > lateral leminiscus > inferior colliculus > MGN > Auditory cortex

Where does the auditory pathway split to go both contralaterally and ipsilaterally

the ventral and dorsal cochlear nuclei

Reception

capturing pressure changes

pathway of sound to ear

pinna > ear canal > ear drum (tympanic membrane) > ossicles > semicircular canals > cochlea

Function of the stapes

pushes against the oval window, transferring pressure waves from air to fluid in the scala vestibuli

What does the Organ of Corti have?

hair cells (auditory receptor cells)

pressure waves ascend to the apex of the cochlea in the scala vestibuli

then, pressure waves descend to the base within the scala tympani and transfer force to the round window

Information from one hair cell is encoded in ____________________

many neurons OR one neuron that branches

What to remember about innervation of hair cells?

they have different patterns of innervation

What to remember regarding hair cell orientation?

they have the same orientation

What is sensory signal transmission?

turning a physical stimulus into neural activity

what does transduction look like for the auditory system?

turning pressure waves into changes in membrane potential

What are auditory receptor cells also called?

hair cells

What is the function of tip links between stereocilia?

they detect a change in mechanical force

What is the driving force of K+ for a hair cell Apical surface?

inward, K+ depolarizes the hair cell

What is the driving force for K+ on the basal surface of a hair cell?

outwardWh

What is the resting membrane potential for a hair cell?

-45mV

What does the efferent synapse do?

Inhibits/gains control to reduce firing rate in the afferent nerve

efferent synapse mechanism/gain control mechanism

releases ACh, ACh receptors are Ca2+ permeable, causes influx of Ca2+ though sK channels

efferent synapse mechanism (after Ca2+ influx)/ gain control

efflux of K+ through sK channels causes hyperpolarization, reduces rate of ACh release to afferent nerve endingWht

What does the reduction of ACh release cause in the efferent synapse mechanism/ gain control

the reduced rate of ACh neurotransmitter reduces firing rate and probability of AP firing

Where are high frequency signals encoded?

near the base of the cochlea

where are low frequency signals encoded?

near the apex of the cochlea

what is tonotopy

the spatial arrangement of where auditory cells are transmitted, received, and perceived

In which areas is there tonotopy?

in the cochlea and auditory cortex

what is the cochlea?

the inner ear structure that sends information about sound to the brainwhat

what is the auditory cortex?

the part of the brain that receives and interprets sound information

What does the cochlear nucleus encode?

intensity and frequency

what does the pattern of action potential spikes encode in the cochlea?

tonotopic frequency

How do the layers of the auditory cortex effect tonotopy?

different frequency signals project to different sections of the cortex, spatial organization of information encoded in the cochlea and where its going to in the brain