ENT Flashcards
What is used to test hearing range?
Audiogram (the higher up the better the hearing)
- 20-40 = moderate hearing loss
- 70-90 = severe hearing loss
Function of external ear?
Receives sound
Function of middle ear?
Tympanic memrane : oval window ratio?
Acts as an amplifier
* 18:1 (impedance matching air to liquid)
Closure and opening of eustachian tube?
Function of tube?
Resting state of cartilaginous tube is closed but opened by tensor veli palatini & levator palatine muscles
*pressure equalisation in ears (dysfunction leads to middle ear negative pressure)
Oval and round windows?
Function?
2 openings of cochlea into middle ear
* transmission of pressure wave + vibration of basilar membrane
What causes fluid vibration?
Explain how vibration is picked up by basilar membrane?
Movement of stapes via stapedius (smallest skeletal muscle in the entire body)
- High frequency sound at beginning of membrane
- Low frequency sound towards apex (end of the spiral)
Function of inner ear?
Structure?
What is found in centre?
Receiver/transducer (fluid -> AP)
- Spiral lamina wrapped around central modiolus
- cochlear nerve found inside central modiolus
Explain structure of cochlea
What do these open up into?
Scala media (endolymph) suspended in between scala tympani & scala vestibuli (perilymph)
- Scala vestibuli = oval window
- scala tympani = round window
Ionic composition of periplymph and endolymph?
Perilymph
* Na+
Endolymph
* K+
Explain central pathway of sound perception? (5)
Organ of Corti depolarises and fires
Stimulates VIIIth nerve and then central pathways
E COLI
- Ear ->
- Cochlear nucleus ->
- superior Olivary complex ->
- Lateral lemniscus ->
- Inferior colliculus
Where is primary auditory cortex?
Posterior superior temporal gyrus
When can foetus hear?
18 weeks - foetus can hear
26 weeks - foetus will respond to sound/voice
Universal neonatal screening for hearing loss?
OAEs can be identified in normal cochlea - if absent, suggest a problem
Explain how cochlear implant works
- Inserted into scala tympani
* Will coil around cochlear nerve
Normal development of hearing/vocals? (5)
- 3 months - cooing, recognises mother’s voice
- 6 months - babbling, makes happy and sad sounds, eyes towards sounds
- 12 months - mama/dada, follows instructions
- 12-18 months - syllable deletion/substitution
- 24 months - two word phrases, 50+ words, understands questions and follows commands
Explain balance input/output to central pathway?
Input (4)
- visual
- cardiovascular
- vestibular
- proprioceptive
Output (2)
- vestibulospinal tract
- vestibulo-ocular reflex
Explain the input/output involved in Rombergs test? (standing on foam)
Input = vestibular Output = vestibulospinal
(if fall over = positive rombergs)
vestibular nerve supply to inner ear?
- Superior vestibular nerve = lateral, anterior semi-circular canal, and utricle
- inferior vestibular nerve = poserior semi-circular canal and saccule
Hair cells of inner ear? (2)
Mechanism?
- Kinocilium = longest hair
- stereocilia = the rest
Movement of hair cells towards longest = depolarises (increases firing rate)
If movement away from longest = hyperpolarised (decreases firing rate)
Otolith organs?
Explain structure
Utricle and saccule
* maculae of these organs have stereocilia projecting upwards into gel membrane + otoconia (the gel membrane pulls the hairs in different directions)
What allows the head to perceive position and movement when tilting head or making horizontal movements?
Otolith organs
Also in a lift, it is your otolith organ that allows you to sense whether you’e going up or down even tho you can’t see
how many semi-circular canals are there?
Orientation?
3 on each side of the head
- lateral
- anterior
- posterior
They are paired
* orientated at 90* from each other
What is the ampullary capula?
Function?
Sits in ampulla of semi-circular canal
- it is pushed by perilymph in opposite direction response to movement
- “bending” cause cilia to deflect
- sends signals to vestibular nerve
Vestibulo-occular reflex input and output?
- input: vestibular
- output: vestibulo-ocular reflex
(hold thumb, look at it, turn head)