Lecture 19 - Hearing II Flashcards
Composisitons of the inner ear?
3 semicircular canals, vestibules, cochlea
Cochlea?
fluid-filled tube spiral around bony core (modiolus), containing auditory nerve and vascular supply
Modiolus?
bony tube filled with fluid - perilymph - with composition similar to ECF (Na 140mM, K 5mM)
Scala media fluid?
high K low Na
Organ of Corti?
20,000 sensory hair cells
Hair cell types?
inner hair cells: 25%, single row, innervated by Type I afferent cells (90% of afferents); outer hair cells: 75%, innervated by type II afferent cells, the type of cells efferent fibres predominately innervate
Sound transduction - bones to basilar?
displacement of the stapes on the oval window, and then round window, initiates a travelling wave of displacement along the basilar membrane and the organ of Corti, reaching a peak amplitude at a region corresponding to its frequency
Sound transduction - basilar to neuron?
vibration of cochlea displaces organ of Corti, displacing stereocilia, causing ion channel opening resulting in depol and hyperpol across membrane, leading to glutamate release an innervation of auditory nerve
Myosin?
connected to actin & maintains tension between cilia for selective activation
K+ gradient?
high in scala media, moves to low scala tympani
Inner hair function?
CNS sensory input, innervated by 90-95% of afferent CN VIII
Outer hair cell function?
enhance or amplify small motion of cochlear partition, increasing sensitivity & f selectivity; depol causes cell contraction w ‘prestin’ proteins at specific frequency to aid transduction
Place principle?
frequencies of sound innervate corresponding basilar membrane stereocilia based on tonotopicity; the base is narrow and stiff w high f and the apex wide and floppy w low f
Temporal coding of frequency?
f below 1000-2000 (apex) have their firing synchronised, with the incoming sound known as phase locking
Meniere’s disease?
abnormal fluid homeostasis leading to hearing loss
