Hearing and the Ear Flashcards
What is human hearing range
20Hz- 20kHz
What is optimal human hearing
500-3000Hz
What happens with normal ageing
There is a decline in hearing sensitivity particularly at the high end
Which part of the ear contains goblet cells
The middle ear
Where can you get ear infections
In the middle ear as it contains goblet cells which are secretory
What is the inner ear responsible for
Sensory transduction
What do you use to view the tympanic membrane
Otoscopy/ auroscope
What is the tympanic membrane involved in
Conduction of vibration, therefore issues result in conduction related hearing loss
What is serous otitis media
A problem with drainage along the Eustachian tube often linked to respiratory infection, common in children
What do you do if children have issues with drainage along the Eustachian tube
Grommets are pushed through the tympanic membrane to provide an alternative drainage route. Grommets drop out spontaneously and the tympanic membrane heals
What are the ossicles
Malleus (hammer), incus (anvil), stapes (stirrup)
Describe impedance matching
The tympanic membrane has a large surface area but force generated by sound vibrations in the air is weak. Ossicles concentrate the force onto the smaller area of the oval window increasing the efficiency of transmission of the vibrations to the fluid filled inner ear which increases the sensitivity of the ear by a factor of 1000
What is oesteosclerosis
Calcification of the joints where the foot of the plate of the stapes inserts into the oval window. Runs in families, more common in females, age on onset typically 15-35, may be triggered by oregnancy
How you you treat osteosclerosis
Prosthetics are inserted via microsurgery to attempt to fix the problem
What are the 3 chambers of the cochlear
Scala vestibuli, scala media, scala tympani
Where is the basilar membrane
Located directly below the scala media
What is the organ of corti
The hearing organ
What are the hair cells in the organ of corti called
Stereocilia (are microvilli not cilia)
What are the stereocilia held up by and why
The basement membrane so that they are in contact with the tectorial membrane
What does the tectorial membrane do
Pushes cells from side to side
Describe stereocilia
All different heights and reflex in one direction resulting in excitation onto the dendritic end of an axon
What moves and what is fixed in the organ of corti
The basiliar membrane moves, the tectorial membrane is fixed
Describe perilymph
Found in scala vestibuli and and scala tympani. Made up of everything apart from apical cells, Has high sodium concentration and low potassium concentration. Originates from blood plasma and CSF
Describe endolymph
Found in scala media. Has a low concentration of sodium and high concentration of potassium. Originated from stria vascularis and contains and electrogenic Na+/K+ pump
Compare the endolymph to the perilymph
Endolymphy is +80mv resulting in endocochlear potential
What is Waardenburg syndrome
Cells that control K+ ion secretion into the stria vascularis fail to migrate into the tissue during development leading to deafness because there is no endocochlear potential
What happens when sterocilia are deflected
K+ channels on the surface open and K+ flows into the cell due to the driving force of the endocochlear potential. This depolarises the hair cell which leads to transmitter release
What are the stretch-gated channels on the stereocilia called
Tip links
Describe inner hair cells
One row, 3,500 in number, role is pitch determination and they don’t regenerate
Describe outer hair cells
Three rows, 12,000 in number, role is cochlear amplifier
Describe cochlear amplifier
Outer hair cells contract when they are excited by the waves passing along the basilar membrane. When excited the outer hair cells depolarise resulting in them changing size and sinking. Effectively outer hair cells bounce on the basilar membrane in phase with the wave which increases the size of the wave on the membrane. Oscillations in phase result in a dramatic increase in amplitude. Depolarisation is brought about by electrical potential (controlled by sound loudness)
Describe cochlear microphones
When the ear is damaged, the hairs may oscillate in the absence of external sound. This can cause the basilar membrane to vibrate and act as a loudspeaker that emits sound
Describe difference tones
When two pure tones are presented to the ear, the movement of hair cells generate new waves that interact on the basilar membrane to produce a third peak- perceived as a sound by the brain, but this does not exist in the real world. The frequency of the difference tone:
ft = f2 – f1 e.g. for f1= 1335hZ and f2= 1600 Hz one solution is ft= 1600-1335 = 265 Hz. Difference tones can only be produced if the hair cells are functional
How are difference tones used to diagnose cochlear deafness
Providing an objective measurement of hair cell damage, useful in patients who can’t give a subjective response (e.g. babies or dementia suffers). NB DPOAE- distortion product otoacoustic emissions. Two high tones produce a low tone, this can be used to test hair cell function
When does conductive hearing loss occur
When there is a problem with the outer and/or middle ear
When does sensori-neuronal hearing loss occur
When there is a problem with one or more of the cochlearm auditory nerve or central auditory pathways
