Physiology of Hearing and balance Flashcards
What causes sound?
Oscillating molecules
What does frequency dictate?
Pitch
What does amplitude dictate?
Intensity
What frequencies can humans perceive?
20Hz - 20,000Hz
How does the middle ear act as an amplifier mechanism?
Ossicular chain acts as piston or lever arm with varying efficiency depending on frequency of sound transmitted
What is the tympanic membrane: OW ratio?
18:1
What is the eustachian tube?
Ventilation pathway for middle ear mucosa
What is the eustachian tube made up of?
Bone and Cartilage
What opens the eustachian tube?
Tensor veli palatini
Levator palatine muscles
What can eustachian tube dysfunction lead to?
MIddle ear negative pressure
What are the oval and round windows?
Openings of the cochlea to the middle ear
What do the windows permit?
Transmission of pressure wave in enclosed canal and vibration of the basilar membrane
Where is the scala media found?
Suspended in between scala tympani and scala vestibuli
What is the cochlea?
Coiled tubes of liquid
Which part of the cochlea has a different ionic composition?
Scala media
Where is the auditory area?
Primary auditory cortex in the temporal lobe
When can a foetus hear sound?
18 weeks
When can a foetus respond to sound/voice?
26 weeks
What % of infants have profound hearing loss?
1/1000
How does the universal neonatal screening test hearing?
The outer hair cells produce sounds which will respond to stimulus
What should children be able to do by 3 months?
Cooing
Recognising mothers voice
What should children be able to do by 6 months?
Babbling
Turns to sound or eyes towards sound
Makes happy and sad sounds
What should children be able to do by 12 months?
May make simple noises, mama/dada
Turns to sound
What should children be able to do by 18 months?
Says a few words Colours Animal sounds Recognises body parts Simple commands
What should children be able to do by 24 months?
Two word phrases, 50+ words
Understands questions and follows commands
What should children be able to do by 36 months?
Use 3 word sentences, aware of rhyme, start with adjectives, understand order, positioning
What 6 systems contribute to balance?
Visual Proprioceptive Vestibulospinal tract Cardiovascular Vestibular Vestibulo-ocular reflex
What does the Superior vesicular nerve supply?
Lateral/Anterior SCC and utricle
What does the Infetior vesicular nerve supplY?
Posterior SCC and saccule
What are the 2 hair cells of the inner ear?
Kinoclium and stereocilia
What is the resting potential of the hair cells of the inner ear?
Resting potential 90 spikes/sec
How are otolith organs oriented?
At right angles to eachother
Where is the capula found?
Ampulla of SCC
What causes deflection of the SCC?
Movement of the perilymph
What causes the stereocilia to deflect?
Bending
What happens when one side is excited?
The other is inhibited
What is the vestibulo-ocular reflex involved in?
Focusing on an object when the head is moving
When would the brain percieve rotation when stationary?
When a patient has lost one ear
Brain sees high stimulus from the working side and no stimulus from the other side, so eyes flicker causing the patient to become dizzy
What do the central pathways have outputs to?
Vestibulospinal tract
Medial longitudinal fasciculus and ocular muscles
Medial lemniscus and thalamus to cerbrum
