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Auditory System - Coggle Diagram
Auditory System
:star: Middle Ear:
Bones - Malleus, Incus and Stapes - synovial joints
Muscles - Tensor Tympani and Stapedius
Tubes - Eustachian Tube
Role: acoustic impedance match, between air and fluid-filled inner ear
Amplifying the movement makes it louder
Lever action of ossicles
Malleus > Incus
Innervation: glossopharyngeal nerve
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Role of muscles in the middle ear:
Protection of the inner ear from acoustic trauma, stiffens the ossicular chain - protects inner ear from loud sounds (acoustic reflex), fine-tune sound transmission
Stapedius stimulated acoustically
Reflex arc 3 or 4 neurones
Tensor Tympani - voluntary and involuntary control
Role of Eustachian Tube: ventilation of middle ear space, drainage of secretion
Oval window – receives sound waves from tympanic membrane via malleus, incus & stapes; round window vibrates with opposite phase to oval window allowing fluid in cochlear to move
:star: Inner Ear:
Vestibulocochlear Apparatus - set of fluid filled sacs, encased in bones
Cochlear - responsible for hearing
Labyrinth - responsible for balance
Innervation: Vestibulocochlear nerve, hearing and balance
Cochlear: 2.5 turns fluid filled bony tube, 2 opening - round window and oval window, 3 compartments, 2 ionic fluids
:star: Cochlear Fluids:
- Endolymph (scala media) - high K+ fluid
- Perilymph (scala vestibuli/ tympani) - like ECF and CSF, Na+ rich
Gradients maintained by Na, K-ATPase and NKCC1 ClC-K chlorine channels
Ion channel abnormalities = deafness
:star: Semi-Circular Canals:
Function - detect rotational acceleration and deceleration; gravity and linear detected by otolithic organs (utricle and saccule)
3 arranged in right angles to each other - orthogonal
Part of the Labyrinth
Innervation: vestibulocochlear
:star: Cochlea:
Basilar membrane - base is narrow and stiff, apex is wide and floppy
High frequencies detected at base and low frequencies at the apex
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Hair cells: Inner hair cells - mechanical transduction, Outer hair cells - fine tuning
Base attached to basilar membrane, stereocilia anchored to tectorial membrane
Shearing forces at stereocilia
Inner hair cells: movement of stereocillia, rapid response required, mechanically gated K+ channels opened causing depolarisation (K+ rich endolymph), depolarisation results in opening of voltage gated Ca channels, release of ntm e.g. Glutamate, repolarisation through K+ efflux (into K+ poor perilymph)
Tonotopy: each nerve responds maximally at a specific frequency, outer hair cells can alter the stiffness of basilar membrane to ensure maximal stimulation at one site and dampened response at another, increased resolution
:star: Sound Information:
Frequency (pitch): encoded in nerves by location along basilar membrane
Intensity (loudness): encoded in nerves by numbers responding and by firing rate
Sound transduction: inner hair cells
Amplification: outer hair cells
Types of hearing loss: defective outer/ middle ear = conductive hearing loss
Defective inner ear = sensorineural hearing loss
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:star: Neuron to Brain: auditory fibre, spiral ganglion, spiral ganglion to cochlear nerve, central auditory pathway!
Central Auditory Pathway: ECOLI - eighth nerve, cochlear nucleus, olive, lateral leminiscus, inferior colliculus
Brainstem: Sound localisation - MSO neurons respond only when excitatory signals arrive simultaneously
Anatomical differences in connectivity allow each MSO neuron to be sensitive to sound source from particular location
:star: Outer Ear: Pinna and Ear Canal:
Pinna - cartillagenous structure
- formed from pharyngeal arches 1 and 2 (6x Hilocks of His)
- forms between 10th and 18th week in utero
- directs soundwaves towards ear canal
- high pitch > low pitch
Ear canal - 1/3 cartilage and 2/3 bone