Module 3D ENT - Lectures Flashcards
What is meant by amplitude and frequency?
- Amplitude (difference between the denser and less dense areas of air molecules) = loudness
- Frequency = the number of waves that pass in one second
–> 1 wave per second = 1 Hertz (Hz)
–> The greater the frequency, the higher the pitch.
What is sound measured in?
decibels (dB)
Ear anatomy
- The pinna is the outer fleshy part of the ear
- Sound waves travel down into the auditory canal until they reach the tympanic membrane
- The tympanic membrane moves in relation to the sound waves hitting it –> this moves the 3 bones within the middle ear –> which in turn moves the oval window which is attached to the cochlear
Middle ear anatomy
- what are the 3 bone structures called
- what holds these bone structures in place?
- The 3 bone structures within the middle ear are called the malleus, incus, and stapes –> held in place by the stabilising ligaments and two muscles (stapedius muscle and tensor tympani muscle)
Do the bones of the middle ear amplify the sound or the force against the oval window + why is this beneficial?
- The bones of the inner ear do no amplify the volume of the sound, they amplify the force
- There is a fluid-filled structure within the cochlear which requires more force as it is fluid not air
What is impedance matching in regards to the middle ear and sound?
Impedance matching allows vibration of the fluid in the inner ear –> sound can be transmitted directly to the cochlear through bone
What is the attenuation reflex in regards to sound and the middle ear?
- this describes the action of the two muscles (stapedius muscle and tensor tympani muscle) in response to a very loud sound
- the muscles help to stabilise the bone structures and in turn protects the cochlear from the loud sound
- it also acts to mask low frequency sounds in loud environments –> reducing background noise making speech easier to hear in noisy enivronments
Describe the travel of sound waves from initial entry to the round window
+ what is the round window?
- The sound waves pass through the aduitory canal, through the middle ear, and through to the cochlear
- They hit the oval window (where the stapes are) –> the waves then pass along through fluid called perilymph which goes all around the cochlear (over the top of the Organ of Corti) to the round window
- The round window is a membranous structure at the other end of the cochlear and basically just allows for the transmission of waves
Where does all of the ‘actual hearing’ take place within the ear + where are low/high frequency sounds heard
- The Organ of Corti
- High frequency sounds –> heard at the base
- Low frequency sounds –> heard near the helicotrema
Organ of Corti
- where does it sit
- what does it do in response to vibrations
- Organ of Corti sits in the middle of these two fluid-filled areas –> gets vibrated as the waves pass either side
- Genereates a nerve impulse in response to vibration of the basilar membrane
- Contains specialised cells called inner and outer hair cells
- Synapses with the spiral ganglion of Corti and then the cochlear nerve
. - Perilymph –> Na+ rich
- Endolymph –> K+ rich
What happens when the oval window is pushed in
- Pushing in of the oval window pushes perilymph into the scala vestibule
- The pressure change travels along the scala vestibule, through the helicotrema along the scala tympani and causes movement at the round window
- Causes non-rigid structures within the cochlear to move –> the basilar membrane moves
Organ of Corti - hair cells
- why are outer hair cells important
- The hair cells (inner and outer) are the structures that actually detect the movement of the basilar membrane
- Movement of the basilar membrane relative to the tectorial membrane –> results in displacement of the hair cells
- Inner hair cells are not attached to the tectorial membrane
- Outer hair cells are important for the amplification of sound
What ion is involved in depolarisation of inner ear hair cells?
Hair cells depolarise with K+, unlike nerve cells
Which inner ear hair cell type innervates the majority of spiral ganglion cells?
Inner hair cell
Outer hair cells are responsible for the amplification of sound –> what is the name of the protein which contracts and elongates to amplify sensitivity to sound waves?
Prestin
Auditory pathway –> which cranial nerve is involved?
Cranial nerve VIII (vestibulocochlear nerve)
Primary auditory cortex
- Primary auditory cortex is like a ‘piano’ –> damage to a part of it can knock out that frequency of sound
The Organ of Corti –> YouTube video
https://www.youtube.com/watch?v=bwCz3Q8y-PM
The vestibular system –> what is it?
- The vestibular system provides information on the spatial orientation and movement of the head and plays an essential role in regulating movement of the trunk and limbs as well as the maintenance of body posture
- In addition, afferent discharges from the vestibular organs influence reflex centres responsible for maintenance of a stable retinal image by controlling neck muscles and extraocular eye muscles
- Rotary movement of the head is detected by hair cells in the semicircular canals, while linear acceleration and the direction of gravity are detected by hair cells in the otolith organs
Inner ear anatomy
- In addition to the cochlear, there is the Otolith organs and the semicircular canals
What is Meniere’s disease?
- A transient condition that can last up to 3hrs
- Symptoms –> dizzy, unsteady, nauseous, ringing in ears, and a drop in hearing
- thought to be due to excessive secretion of endolymph with acute swelling in vestibular and cochlear duct –> self-limiting may be due to minor rupture relieving pressure
- Treatment –> betahistine, diuretics, corticosteroids, surgery
Inner ear –> Otolith organs
Inner ear –> semicircular canals
Vestibular nervous pathway