Auditory system Flashcards
What is sound
The displacement of air particles following a sinusoids pattern of compression and rarefaction
How would you distinguish between a quiet and loud sound wave diagram
Greater displacement from the baseline in loud sounds ( greater amplitude)
What is the pinna formed from (embryology)
Pharyngeal arches 1 & 2 ( 6x hillocks of His)
What’s the range of human hearing
20Hz - 20 KHz
Give the 4 main components of the auditory system
Outer ear - air
Middle ear - air
Inner ear - fluid
Central auditory pathways - electrical
What’s the purpose of the folds in our ears
Filter out lower pitch sounds which are less functionally important
What’s the function of the pinna
Direct sound waves towards the ear canal
What is the bone and cartilage composition of the ear canal
Medial 2/3 is bone and lateral 1/3 is cartilage
What type of epithelium is the tympanic membrane made of
Name the top 1/3 and bottom 2/3 of the tympanic membrane and explain the difference
Top - pars flaccida
Bottom - pars tensa
Bottom contains endoderm, ectoderm and mesoderm but top only has ectoderm and endoderm so the top is much more delicate
What 3 bones (ossicles) does the middle ear contain. Give them in order of size
Incus
Malleus
Stapes
What 2 muscles does the middle ear contain
Tensor tympani
Stapedius
Where is the Eustachian tube found
Middle ear
How much energy is lost when it is transferred from air to fluid
99.9% loss of energy
What is the role of the middle air and how do the ossicles faciliate this
Amplification of the airbone sound vibration
How do components of the mid ear facilitate its function
Area difference between tympanic membrane and stapes ceates large pressure difference
Ossicles are connected and act together to create a lever mechanism
The amplification gain is 18x or 20-35 dB
What’s the role of muscles in the middle ear and how do they carry out this role
Protection of the inner ear from acoustic trauma
Reflex arc of 3/4 neurones that stiffen the ossicular chain in the presence of loud sounds
How are the stapedius and tensor tympani stimulated
Stapedius - stimulated acoustically
TT - voluntary and involuntary control
What does the eustachian tube connect
Middle ear cavity to nasopharynx
Whats the purpose of the E tube
Ventilate the middle ear space and drain secretions
Where is the vestibulocochlear apparatus found and what innervates it
Set of fluid filled sacs encased in bone in the Inner ear
CN VIII - vestibulocochlear nerve
What is the cochlea responsible for
Hearing
What is the labyrinth responsible for
Balance
What are the 3 compartment of the cochlea and which is not connected to the other
Scala tympani
Scala media - independent from the others
Scala vestibuli
How many turns does the cochlea have
2.5 turns
Guve the 2 openings on the cochlea
Round window
Oval window
The cochlea contains ionic fluids. Give their names, locations and compisitions
Endolymph - scala media , hight in K+
Perilymph - scala tympani and vestibuli, rich in Na+
How are gradients of cochlear fluids maintained
Na, K ATPase
Chlorine channels
Describe the movement of sound in the cochlea
Stapes footplate presses on the oval window which develops a pressure wave within the scala vestibuli
Wave progresses round through the helicotrema and into the scala tympani
The wave then hits the round window
Compare the base of the basillar membrane with the apex
Base: narrow, stiff and detects high frequencies
Apex: wide, floppy and detects low frequencies
Where in the cochlea does fluid energy start moving to electrical energy
Organ of corti - sits above basillar membrane and contains hair cells
Desribe what occurs when the inner hair cells move
Mechanically gated K+ channels opened causing depolarisation (K influx from endolymph)
Depolarisation resukts in opening of voltage gated calcium channels
This results in naurotransmitter release - usually glutamate
Repolarisation occurs through K+ efflux into perilymph
What is meant by single nerve fibre response
Each nerve responds maximally at a specific frequency
Whats the role of outer hair cells in the scala media
Alter the stiffness of the basillar membrane to ensure maximal stimulation at one site and dampened response at another site
Increased resolution
How are frequency, intensity and amplification encoded
Frequency - in nerves by location along the basillar membrane
Intensity - in nerves by numbers responding and firing rate
Amplification - oute hair cells
Give the central auditory pathway
Eight CN Vestibulocochlear nerve Cochlear nucleus Olive ( sup,med, inf olivart nucleus ) Lateral leminiscus Inferior colliculus
ECOLI
