Auditons Flashcards
What is the route sound takes into the ear
Tympanic membrane -> malleus -> incus -> stapes -> oval window -> cochlea moving the lymph which is inside which moves the basement membrane which moves the hair cells
What is the Eustachian tube and what does it do
It is a tube which connects the middle ear to the nasopharynx. It allows air pressure to equalise on both sides of the tympanic membrane. Empties into the nasal passages. By swallowing and yawning the valve can open and the pressure can equalise. Children is smaller tube so they are more prone to infections
What are the ossicles what do they do
Are the three small bones - malleus, incus and stapes. Transmit the vibration from the tympanic membrane to the oval window.
What is the oval window
Where they ossicles trainsmit the vibrations to, cochlea is behind the oval window and contains the apparatus which transforms the vibrations into a neural response
What mechanisms are used to amplify the sound
For pushing something / surface area
Force pushing is amplified by the ossicles
And the surface area of the oval window is smaller than the tympanic membrane so the pressure is amplified allowing for movement of the fluid in the cochlea
What is the attenuation reflex
Response to low sounds. The muscles stapedius and tensor tympani when contracted prevent the movement of the ossicles so prevent sound transmissions.
Prevents receptor saturation at loud sounds and this can be reduced by the reflex.
Protect from damage of loud sounds but this could already cause damage due to the reflex delay.
Allow us to understand conversation in a noisy environment as the reflex suppresses low frequency more than high frequency
What is the labyrinth
It is part of the vestibular system and is concerned with balance
What is the cochlea
It is shell shaped hollow tube made of bone with a central pillar called the midiolus ant the base is the oval window and the round window
What are the three layers of the cochlea and what do they contain and what separates them
Top Scala vestibule Middle scala media Bottom scala tympania V and m separated by the Reissner's membrane V contains perilymph M and t separated by the basilar membrane M contains endolymph T contains perilymph
What is on the basilar membrane and what does it do?
Organ of corti and this is where mechanical vibrations are transformed into neural energy generation
How are the vibrations transmitted from the oval window
The vibration at the oval window -> transmitted to the perilymph causing an increase in fluid pressure in the scala vestibuli -> scala tympani to the round window
What happens at the basement membrane
The motion of the perilymph moves the basement membrane which has rods with stereocilia on it which when they move they cause a depolarisation to the cochlea nerve
Depending on how far along the basement membrane moves determine the frequency of the sound. This is responsible for the neural coding of pitch
How does the bending of the stereocilia lead to neural energy generation
When stereocilia move one way they depolarise and then the other way they hyperpolarise.
Depolarisation is caused by the opening of the K+ channels called TRPA1 allow k+ entry so they depolarise opening voltage gated Na+ this allows NT vesicles to move and synapse with the bipolar nerve.
Other at they then close and hyperpolarise
There are 2 types of hair cells what are they called and how do they differ?
Outer hair cells out number inner hair cells by 3x but their innervation differs
Inner hair cells have 95% of the innervation and outer hair cells have 5%
Outer hair cells are known as amplifiers they have membrane motor proteins which can change the length of the outer hair cells this movement of cells causes movement in the basilar membrane which therefore changes the relationship between the cochlear membranes
What is characteristic frequency
Each neurone responsive to sound at one frequency and that is a characteristic frequency. Most spiral ganglion cells receive input from one inner hair cell at a particular location at the basilar membrane so fire AP at this limited frequency range
