Hearing taste and smell Flashcards
Amplitude and frequency are the two characteristics of sound but what are they responsible for?
frequency/wavelength = pitch of the sound
amplitude = intensity/loudness fo the sound
Explain the process of hearing
look at diagram
1) first transduction: sound waves strike the tympanic membrane and become vibrations
2) sound wave energy is transferred to the three bones of middle ear, which vibrate
3) 2nd transduction: stapes is attached to the membrane of the oval window. Vibrations of the oval window create fluid waves within the cochlea
4) 3rd transduction: fluid waves push on the cochlear duct , hair cells bend and release NT
5) 4th transduction: NT release on to sensory neurons creates AP’s that travel through the cochlear nerve ot the brain
6) energy from the waves transfers across the cochlear duct into the tympanic duct and is dissipated back into the middle ear at the round window.
What constitutes the outer (external) ear?
- Pinna (auricle)
- External auditory meatus
+ cartilaginous and bony parts are not in the same direction (hence we need to pull the ear posterosuperiorly when examining it)
What can you do to differentiate between a TMJ pain and external auditory meatus pain?
tap on the tragus and if it hurts then most like to be EAM
what gland is in the EAM and what is its function?
ceruminous glands
- release cerumen (ear wax|) which allows ear drum to be soft and waterproof, prevent laceration of the EAM when under water
What nerves supply the EAM?
auricular branch of X
auriculotemporal branch of V
explain the structure of the tympanic membrane and what you might see on examination
- concave
- shadow of the handle of the malleus - this splits the membrane into 4 quadrants
- safest quadrant is the antero-inferior but all the fluid also collects here: chorda tympani is in the posterosuperior quadrant
- triangular reflection of light in the AI quadrant (Politzer’s traingle)
Explain what is contained within the middle ear
air filled cavity with ossicles, 2 muscles (stapedius and tensor tympani muscle) and nerve (chroda tympani)
- ossicles are attached to the walls by ligaments
- middle ear connected to nasopharyn by the auditory/pharyngotympanic/eustachian tube
what is the middle ear supplied by?
glosspharyngeal (because mucous membrane is continuous with pharynx)
why are the roof and floor of the middle ear impo?
as they are very thin bones, infection of the middle ear could leak through these. if through the roof could causes meningitis or encephalitis. if through the floor could cause haemorrhage of the int jug vein
infection in ME could also spread into the mastoid sinus
by how much do the ossicles magnify the sound as it goes into the inner ear and why?
15x magnification
- because the inner ear is viscous the sound waves need greater energy to move through
where do the tensor tympani and stapedius attach and what is their role?
- tensor tympani (mandibular nerve) attaches to the handle of the malleus –> pulling the tympanic membrane medially therefore tensing it during loud sounds as name suggests –> reduce vibration of tympanic membrane
- stapedius (VII) is attached to the stapes –> when contracted it pulls the base fo the stapes away from the oval window therefore not all the vibrations are transferred into the inner ear –> protecting the inner ear from loud sounds
what happens if the middle ear muscles are not functioning properly?
hyperacusis- pt have constant tinnitus
as the walls of the pheryngotympanic tube are normally collapsed, how can they be actively opened adn why would you want do so?
to restore the nromal pressure within the middle ear the walls can be actively opened through swallowing or blowing while pinching nose
- simultaneous contraction of the tensor veli palatini and salpingopharyngeus muscles to do this
how does the pharyngotympanic tube differ in children and why is this impo?
shorter and straighter in children - infection can spread more easily
what constitutes the inner ear?
bony labyrinth - vestibule \+ utricle \+ saccule - semicircular canals \+ducts - cochlea
Membranous labyrinth is within the bony labyrinth containing all of the above and filled with endolymph and surrounded by perilymph
where is the spiral ganglia located and what is its function?
located within the cochlea and they are the ganglia for the cochlear nerve
what are the three ducts within the cochlea?
- scala vestibuli (end of this is the oval window covered by stapes)
- cochlear duct (more impo in hearing)
- scala tympani (end of this is the round window covered by membrane to allow to compensate for pressure changes when the stapes goes back and forth to create the sound waves)
the two scala ducts are filled with perilymph and connected at the helicotrema (apex/tip of the cochlea) - therefore sound waves goes form oval window –> SV –> helicotrema –> ST –> round window
what separates the ducts within the cochlea
- vestibular membrane separates SV from CD
- basilar membrane separates ST from CD
Where are the hearing receptors located
organ of corti - on the basilar membrane
tectorial membrane projects over the organ of corti
how does the ear differentiate between different frequencies?
the basilar membrane is thicker (short and stiff) at the cochlear base and thin (long and floppy) at the end - high frequency at the base and low at the apex
When the basilar membrane vibrates at the resonant frequency, it absorbs all the kinetic energy of the wave and effectively stops it at that point.
how is the signal detected at the organ of corti
upward deflection of the basilar membrane moves the inner and outer hairs laterally with respect to the tectorial membrane
inner hair cells = cochlear nerve endings terminate here
outer hair cells = increase sensitivity of inner hair cells (means we can listen to each with a lot of background noise) - cochlear tuning
explain the process of signal transduction that allows us to hear
displacement of the stereocillia in one direction opens K channels, and closes them in the other
explain the process of cochlear tuning
inner hair cells depol –> send signal to cochlear nerve –> which is connected to cochlear nuclei –> which is connected to sup olivocochlear nucleus –> fibres alogn this path release Ach onto the inner hair cells causing them to depol and dampening down hearing in areas of pitch which are of no interest (background noise)
