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Audition (Nerves projection (1st order neuron (Spinal ganglion,…
Audition
Nerves projection
1st order neuron
Spinal ganglion
Divergence
2nd order neuron
Brain stem
Bilateral projections
3rd order neuron
Medial geniculate nucleus to primary auditory cortex
Fibers form internal capsule
Wernicke area
Area for intepretation of language
Decussatate
both cortices receive input from both ears
Unilateral lesions of ascending pathway
No monoaural deafness
2 auditory inputs
Function
Sound
Pressure
Amplitude
0 to 120dB
120 - Threshold of pain
Frequency
20 to 20000Hz
Amplitude
Impedance matching
Middle ear and inner ear
Vibrations in liquid matches the vibrations in air
Vibrations in the tympanic membrane
Large vibrations on oval window
Amplifying the vibration
Middle muscles protect against large sounds
muscles stiffen when sounds occur
Prevent vibrations getting into the ear
Cochlear
Scala vestibuli
Scala media
Basilar membrane
Cuts the cochlear in half horizontally
Basilar membrane vibration
Codes pitch
Conical shaped
amplitude is greatest at the centre of the cochlear
Coding of volume
Pattern of vibration increases as a low frequency hits the oval window
Transduction
Hair cells
#
Attached to Basilar membrane
Tectorial membrane
Too sensitive lead to damage easily
Organ of corti
Potassium channels open
Graded potentials lead to action potentials
Lower frequency higher graded potential
Higher frequency lower graded potential
Higher frequency is harder to hear
Anatomy
Outer ear
Pinna/Auricle
External auditory meatus / Tube
Tympanic membrane / Ear drum
Perforated eardrum
pain, ringing, hearing loss
Purpose
Middle Ear
Malleus
#
#
Incus
#
Stapes
#
Internal auditory meatus/ Eustachian tube
equalises pressure on both sides of the membrane
Inner ear
Semicircular canals
Oval window
Round window
Cochlear
Scala media
cochlear duct
Filled with perilymph
Scala vestibuli
Ends at oval window
Scala Tympani
Ends at round window
Synovial joints - Loss of mobility between bones lead to less sensitive hearing
Nerve deafness - Prebycusis (Loss for high frequencies due to over aging and loss of sensitivity)