Basics Flashcards
What is the function of the outer ear?
Capture sound and focus it on the tympanic membrane
Amplify some frequencies by resonance in the canal
Protect the ear from external threats
What is the function of the middle ear?
Focus vibrations from the large surface area (tympanic membrane) onto a smaller SA (oval window) - the change in SA means the pressure is increased.
Using leverage from the incus-stapes joint to increase the force on the oval window
What is the function of the inner ear?
Transduce vibrations into nervous impulses
Produce a frequency (pitch) and intensity (or loudness) analysis of the sound
What are the 3 parts of the cochlea?
Scala vestibuli and tympani - bone structures that contain perilymph (high in Na)
Scala media - Membranous structure containing endolymph (high in K) also where the Organ of Corti is located
If I uncoiled the cochlea, which part is touching the vestibular membrane, which part is touching the basilar membrane in which part sits in between the two?
VM - Scala Vestibuli
Middle - Scala media
BM - Scala tympani
What membrane does the Organ of Corti lie in?
Basilar membrane
The basilar membrane is arranged tonotopically, using the same principle as a xylophone meaning what?
It is sensitive to different frequencies at different points along its length.
At the base is detects high frequencies as it is narrow and tight (like a xylo.) and at the apex it detects low frequencies as it is wide and loose.
The organ of Corti contains thousands of what? How are they arranged?
Inner and outer hair cells.
Inner hair cells are arranged on one column and outer hair cells are arranged on three.
What does the tectorial membrane do?
It is located above the hair cells allowing hair deflection, which in turn depolarise the cell.
Only OHC hairs are in constant contact with the tectorial membrane and these assist the contact with the IHC.
How do IHC and OHC differ on the information they carry?
IHC’s function is to transduce sound into nerve impulses - afferent information to the auditory nerve.
OHC’s function is modulation the sensitivity of the response to the sound - efferent information from the AN.
What are the hairs of the hair cells called? How do they work?
Stereocillia will deflect towards the longest cillium and this will open K+ channels.
The ionic interchange depolarises the cell and the neurotransmitter is freed.
Louder sounds will cause more deflection and so more K+ opening and so more NT release.
Describe the path of the nervous impulses from the cochlea to the brain.
- Spiral ganglions from each cochlea project through the auditory vestibular nerve to the cochlear nuclei on the same side.
- Here, information crosses over at the superior olive level to the other side - though it still carries on the same side too (it’s now on both sides).
- Here, it is symmetrical - Superior Olive -> Inferior Colliculus - Medial Geniculate Body -> Auditory Cortex
How is the auditory cortex arranged?
Tonotopically (arranged by frequencies)
What is the human range of hearing?
20-20k Hz
0-120dB at sound pressure level (SPL)
