Case 4 Flashcards
What is the range humans detect sound in?
20Hz to 20KHz
Which range do we understand speech in?
500-4000Hz
Why is the pressure at the oval window greater than tympanic membrane?
Smaller surface area and greater force due to liquid rather than air behind it
Force on oval window is 20x more than tympanic membrane
What happens when the tensor tympani and stapedius contract?
Chain of ossicles become rigid, and sound conduction to inner ear is diminished
This is the attenuation reflex triggered by loud sounds
What is the structures of the inner ear?
Cochlear- auditory system
Labyrinth - body equilibrium (vestibular system)
What connects the scala tympani and vestibuli ?
Helicotrema
What’s special about the basilar membrane?
Base: narrow and stiff sensitive to higher frequency
Apex wide and floppy sensitive to lower frequency
What are cells and membranes of the spiral organ of corti?
Inner hair cells, outer hair cells, supporting cells
Basilar and tectorial membranes
What happens at the spiral organ of corti?
Staples tap on oval window> fluid vibrates in scala vestibuli and transfers it to scala media and basilar membrane > endolymph rushes through area between tectorial membrane and hair cells > hair cells shear against tectorial membrane > stereocilia on hair cells move towards/away kinocilium > the stereocilia have protein channels and tip links connecting the channels
What happens in the inner hair cells?
If the stereocilia moves toward the kinocilium - potassium and calcium ions move into hair cell > depolarisation > release glutamate > AP in periphery process to spiral ganglion> central process to cochleae nerve
What happens in the outer hair cells?
If loud noise - nerve from olivocochlear bundle releases Ach > binds to OHC channels > potassium ions leave the cell. > hyperpolarisation > Preston cells molecules relax > cell lengthens > basilar membrane moves down reducing vibration > decreases HC activation
To distinguish different frequencies - same as above but Preston molecules contract > decreasing cell length > HC is then activated
What is the vestibule?
Made up of outer bony labyrinth - vestibule w/ Perilymph; inner membranous labyrinth - saccule and utricule w/ Endolymph and maculae
What is the maculae?
Floor of utricle w/ stereocilia pointing upwards and in saccule with stereocilia pointing downward
What is the function of utricle and saccule?
Utricle - horizontal linear acceleration and head tilt
Saccule - vertical linear acceleration and low frequency vibration
What is the otolithic membrane?
Membrane above hair cells which contains crystallised calcium carbonate (otoliths)
How does the vestibule work?
Linear acceleration/hear tilt > otoliths pulls gelatinous membrane in direction of acceleration > hair cell stereocilia move toward/away from kinocilium > potassium and calcium ion move in/no movement > increased/decrease release of glutamate and aspartate > increased/decreased AP down the nerve
What makes up the semicircular canals?
Lateral, anterior and posterior canals
Labyrinth - outer bony semicircular Canals and inner membranous semicircular ducts
Cristae Ampullaris - sensory epithelium
What is the function of the semicircular canals?
Angular/rotational acceleration; maintain dynamic equilibrium (balance and posture)
How does the semicircular canal work?
Rotation > endolymph pushes/pulls onto ampullaris bending the gelatinous membrane (cupula) > stereocilia bends toward/away from kinocilium > depolarisation/hyperpolarisation > glutamate released/or not > AP o not down medial vestibular nucleus > excite/inhibit nucleus and contralateral my excite or inhibit CN VI nucleus > stimulate and inhibit LR of the eyes
It also contralaterally innervates CN III nucleus so excite or inhibit IR of each eyes
What is vestibular nystagmus?
Linear slow phase nystagmus (involuntary eye movements) - caused by dysfunction of the vestibular part of the inner ear, the nerve, the vestibular nucleus within the brainstem, or parts of the cerebellum that transmit signals to the vestibular nucleus
What is the auditory pathway?
Tympanic membrane > ossicles > oval window > scala vestibuli to scala media > endolymph moves hair cells > AP to cochlear branch of CN VIII > cochlear nuclei > superior olivary nuclei > lateral Lemniscus nuclei > inferior colliculus > medial geniculate nucleus > primary auditory cortex
How is the cochlear nuclei divides?
Dorsal and 2 ventral (VPC and AVC)
Dorsal Nuclei give off DAS > majority contralaterally innervate Lat. Lemniscus nucleus directly with some joining DAS and IAS to form the Lat. Lemniscus to the Lat. Lemniscus nucleus
Ventral Nuclei - AVC gives off VAS which bilaterally innervates SON and VPC gives off an IAS which goes off with DAS to innervate contralateral lat. Lemniscus nucleus (majority is direct and some go with VAS as the lat. Lemniscus from the SON
What is the function of SON?
Localisation - lateral is for determining the relative intensity of sound stimulus and medial is for relative timing of sound stimulus
The olivocochlear bundle inhibit basilar membrane vibration