Sensory: auditory and vestibular systems Flashcards
Describe the general structure of vertebrate ears
The pinna (outer ear) is the directional filter, the tympanic membrane sense the pressure difference by vibrating, the columella/ossicles transmit and amplifies/dampens vibrations, the vibrations are transmitted to fluid filled cochlea through the oval window, and travels through the vestibular canal to the tympanic canal, and finally the basilar membrane vibrates and stimulates the receptor cells (hair cells)
What are the properties of the cochlear?
The basilar membrane changes along the length of cochlear. Specific areas vibrates most with specific frequencies (tones), highest frequencies in the first part, vice versa.
Describe the receptor cells in vertebrate hearing.
Several stereovili and cilia forming collar. The cilia and villi are connected by tip links. Vibrations cause stereovilli/cilia to move relative to each other. The tip link directly pulls open stretch sensitive ion channels
What is sound?
Oscillations in air pressure
What happens in the inner ear?
Oscillations in air are transformed to oscillations in liquid
What is Corti’s organ?
The tectorial membrane, inner ear hair cells, outer ear hair cells and the basilar membranee
What happens in Corti’s organ when a cilia is diplaced?
Depolarization of hair cell
Describe the depolarization of a hair cell.
Mechano-electric transduction:
–> influx of K+ and Ca2+ via tip-link ion channels –> influx of K+ –> depol of receptor potential –> spreads to the rest of the cell –> basolateral Ca2+ channels are gated –> Ca2+ influx –> transmitter release –> –>
How does the ear actively control the dynamic range?
By attenuation, adaption and amplification
Describe the complex nature of K+ in hair cells.
K+ depolarizes the cells from the endolymph (high [K+] liquid) in apical end
K+ hyperpolarizes hair cells by efflux in the basolateral end
What are the differnce between inner and outer hair cells in function?
Inner: sends sound impression via afferent fibers
Outer: amplify and filter via electromotility and efferent input
How does the K+ influx in the outer hair cells affect the cells?
K+ influx –> depol –> contraction
Describe the signal route from the cochlear to the brain.
Cochlear –> spiral ganglion –> auditory nerve –> cochlear nuclei in rostral medulla –> superior olive in mid pons (either crossing or not)
(crossing) –> nucleus of lateral lemniscus –> inferior colliculus –> medial genculate (thalamus) –> primary auditory cortex
(not crossing) –> inferior colliculus –> medial genculate (thalamus) –> primary auditory cortex (only skipping the nucleus of lateral lemniscus)
What is the area of speech perception called?
Wernicke’s area
What is the speech producing center called?
Broca’s area
How is the stimuli encoded in the CNS?
Via frequency: firing rate in n. cochlearis single axon is proportional with the local amplitude of basilar membrane
How are the direction of sound source encoded?
By inter-aural time delay (two ears), and by difference in intencity (two ears)
What does the otolith organs cover, and what is it?
Utriculus and sacculus
Perceive gravity
Describe the overall structure of both the utriculus and sacculus. How do they differ?
Striola in the middle, utricular/saccular macula around, where the hair cells are oriented
Sacculus: vertical move, macula oriented away from the striola
Utriculus: horizontal move, macula oriented towards the striola
Where are the otolith organs found?
Overlying the hair cells in the inner ear (in the vestibule)
What is otoconia, and what is the purpose of it?
A layer of small crystals overlaying the gelatanous layer of the otolith membrane. Purpose: to make it heavy so movement can be sensed
What are the difference between the inner and outer hair cells?
Inner: 95 % afferents but only 25 % of the hair cells, transducing sensory perception of sound
Outer: controlling the amplitude of different frequencies (amlification and filtering)
What does a depolarization of the outer hair cells result in?
Contraction –> amplifying the vibrations
What can turning curves be used for?
Identifying the different ganglia cells in the cochlear, as these have different turning curves matching the location on the cochlear
How are the tonotopy throughout the auditory system?
Conserved: matching the frequence from lowest –> highest
What is the semicircular canals, and where are they found?
The organs perceiving rotation
Next to the otolith organs in the inner ear
Describe the semicircular organs.
Semicircle, with ampullae closest to the otololith organs –> where the sensory perception is taking place
How does the hair cells in the vestibule depolarize?
Tip-link meachnically opening K+ channels when the hair cells are bend –> influx of K+
What makes the hair cells in the vestibular system bend?
The hair cells is overlayed by the otolith membrane, which is a gelatinous layer with a crystal layer on top (otoconia). The crystals purpose is to have a heavy layer, that can move the gelatinous layer in response to movement –> hair cells are tipped –> K+ channels are gated –> depol
How is a static gravitational force compared to acceleration on the ottolith organs?
Similar, but as wa have other senses too we can discriminate
Describe the ampullae of the semicircular canal.
Capula surrounding a bundle of hair cells –> crista (enlargement, sensory perception takes place here) –> nerve fibers
What liquid is found in the vestibular system?
Endolymph
How does the endolymph function on the capula?
When the head is rotated, the endolymph will induce a pressure on the capula –> cupula displacement –> hair cells are depoled
How are the hair cells oriented in the semicircular organs?
In the same direction in one ear, mirrowing the other –> opposite response in the two ears depending on the direcetion of rotation
What happens if you keep rotating?
Adaptation: fire rate of ganglion cell will decrease as cupula is coming back to its original position
Describe the central projections of vestibular sensation.
Vestibular nuclei –> ventral posterior nucleus of the thalamus–> parietal lobe
What are the vestibular system used for?
1) postural control together with proprioception
2) eye position for stabilization/compensation for body/head movements
What is nystagmus, and how many different types are there?
Uncontrolable rapid movements of the eye
4: optokinetic, post-rotation, vestibular and caloric
Describe the vestibular ocular reflex (VOR).
When the head is rotated –> semicurcular organs react –> eyes rotate in opposite direction
What is motion sickness caused by?
A mismatch between the VOR and the visual scene –> brain interprets as poison
What are the functions of the vestibular cervicle reflex, and the vestibular spinal reflex?
VCR: stabalizing the head
VSR: stabalizing tthe body
