Hearing Flashcards
What does the outer ear do?
Collects and localises sound ,middle ear protection; skin produces wax and is self cleaning
How does skin shed in the ear canal?
Skin growth starts at the centre of the ear canal and radiates out to the entrance, to stop debris accumulating in the canal.
What is the purpose and origin of cerumen/ear wax?
Produced by sebaceous and sweat glands in the outer third of the ear canal.
Helps clean and lubricate the ear canal; antimicrobial properties; repels water; traps dust and debris with hairs
What can too much wax cause?
A conductive hearing loss due to occlusion.
Constituents of the middle ear
Structure behind malleus
Tympanic membrane note malleus attached to eardrum
Malleus; Incus; Stapes
chorda tympani- sensory branch of facial nerve, tongue
Eustachian tube
Drains middle ear to nasopharnyx
Ciliated to remove mucous produced in the middle ear
Also maintains air pressure across eardrum
Otitis media
Glue ear, middle ear infection. Common in children
Move up eustachian tube?
Why do we need a middle ear?
Air conduction by displacement of ear drum and ossicular chain
Transformer to match low impedance of air to the high impedance of the liquid in the inner ear, thus increasing transfer of sound.
How does the middle ear act as a transformer to overcome the resistance of inner ear fluid?
- Greater area of air drums produces more pressure going onto the stapes
- Malleus arm longer than incus generates greater force at stapes
The cochlea’s structure and the fluids in its cavities
A fluid filled tube spiralling around a central bony core (modiolus) which contains neurovascular structures.
Perilymph, very similar to normal extracellular fluid, high sodium as bathes nerve fibres. The scala vestibuli and scala tympani (below organ of corti).
Middle tube contains endolymph, high in potassium, low in sodium. Made by stria vascularis,
What is the organ of corti and where is it?
Sits on the basilar membrane (above scala tympani?)
Sits near tectorial membrane
The auditory sense organ, comprised of hair cells.
What are the two types of hair cells?
Difference
Note projections are called stereocilia
Inner and outer hair cells.
Inner: Linear; innervated by Type 1 afferent fibres (dominant connection to CNS)
Outer: V/W shaped; innervated by type 2 afferents and also efferents. Local amplifier and tuner
What are the two windows associated with the cochlea?
Oval: where the stapes sits, pressure into scala vestibuli
Round: membrane where pressure releases from scala tympani)
What happens when the stapes moves the oval window?
Sets up a travelling wave. from the base to the apex. moving the basilar membrane and organ of corti. Makes these a frequency filter.
Wave will go to a point of resonance based on frequency, increase in height and then will energy will collpase to sensory cells at that point.
What can be said about the frequency and how far down the cochlea the stimulus will travel
Results in?
High frequencies will terminate a shorter distance from the base than lower frequencies.
Results in tonotopicity
