Sensory Transduction Flashcards
What is the role of the hair cell?
Transduces the stimulus
What are the cilia responsible for?
Stimulus responsive cation entry = cell body releases glutamate onto efferent nerve endings
What regulates the response of cilia to a stimulus?
Afferent nerves
What are the tip links of hair cells?
Specialised structures that gate or close the TMCl channel mouth depending on cilial tilt
What does the tonic release of glutamate from cilia allow?
Modulation of AP frequency
What is sound?
Repetitive variation in a medium (e.g air)
How does sound travel?
Object vibrates which produces changes in air pressure = air vibrates and travels in three dimensions
What effect does sound have on the ear?
Sound vibrates the eardrum and ossicles = this vibration spreads to the cochlea where it is converted to vibration of fluids
What captures vibration in the cochlea?
Hair cells = physical vibration is transduced to neural energy
What are the three mechanisms for impedance matching in the middle ear?
Area ratio of ear drum to stapes footplate = 20:1
Lever action of ossicles
Bucking of ear drum
What does the inner ear contain?
3 fluid filled cavities
What does Reissner’s membrane separate?
Scala vestibuli and scala media
What does the basilar membrane separate?
Scala media and scala tympani
Where is the scala media closed off?
At the apex
Where are the scala tympani and scala vestibuli connected?
At the helioctrema
What structures are in contact with the oval window and round window?
Oval window = scala tympani
Round window = scala vestibuli
Where are hair cells located in the organ of Corti?
Between the basilar membrane and reticular lamina
Where are the tips of the stereocilia of the organ of Corti located?
The tectorial membrane
Where in the inner ear is the perilymph continuous?
At the scala vestibuli and scala tympani
What are the two types of hair cells located in the organ of Corti?
Inner and outer (more numerous) = separated by rods of Corti
Where do the hair cells in the organ of Corti synapse?
On bipolar neurons with their cell body in the spiral ganglion
How does hair cell transduction occur?
Tectorial membrane vibrates and cilia bend = depending on how they bend, hair cells release neurotransmitters which are captured in nerve fibres
What is the direction of the hair cell K+ current?
Inwards = higher K+ concentration than normal in endolymph
What is the membrane potential of endolymph?
80mV = generates a 120mV gradient across the stereocilial membrane
What is responsible for recycling K+ in the endolymph?
K+ channels, transporters and gap junction network composed of 5 different connexins
What can mutations in genes for connexin cause?
Deafness
What properties allow the basilar membrane to detect different frequencies?
Flexible and vibrates in sync with fluid motion
What does the width and flexibility of the basilar membrane determine?
The distance a particular frequency travels
What effect do different frequencies have on hair cells?
Activate hair cells maximally at different locations = hair cells are tuned to different frequencies
What are some features of inner hair cells?
Main source of afferent signal to auditory nerve
10 afferents per hair cell
What are some features of outer hair cells?
Primarily get efferent input
Control stiffness and amplify membrane vibration
Multiple outer hair cells innervated by single afferent
What are the outer hair cells known as?
Cochlear amplifiers
What is the function of the motor protein prestin that is present in outer hair cells?
Located in membrane and can change length of cell
How do outer hair cells respond to sound?
With both receptor potential and change in length
What commonly prescribed drug can inactivate prestin?
Furosemide
What does a change in length of outer cell allow?
Increased basilar membrane movement
What are the two mechanisms the auditory nerve has for frequency coding?
Place code and temporal code
What are the three cochlear nuclei of the auditory nerve?
Dorsal cochlear nucleus
Posteroventral cochlear nucleus
Anteroventral cochlear nucleus
What does tonotopy ensure?
That each neuron innervates several different areas and neuron types
What structure is important for localising sound?
Lateral superior olive
What are some functions of the vestibular system?
Provides info about gravity and acceleration
Serves as reference for somatosensory and visual systems
Allows for sense of orientation
What structures detect angular and linear head acceleration?
Angular = semicircular canals Linear = saccule and utricle
What is the function of the peripheral sensory apparatus of the vestibular system?
Detects and relays info to the vestibular nucleus about head angular and linear velocity
What does the central processing system of the vestibular system do?
Processes info in conjunction with other sensory input fro position and movement of head in space
What does the motor output system of the vestibular system do?
Generates compensatory eye and body movements
What is the function of the semicircular canals?
Detects head movements via rotatory acceleration
What are the crista of the semicircular canals?
Sheets of cells where hair cells are clustered
What does the ampulla of the semicircular canals contain?
Crista = appears as bulge along the canal
What are some features of the semicircular canals?
1 canal for each major plane
Filled with endolymph
What happens to the cupula of the semicircular canal when the head moves?
It is displaced by fluid movement
Where do the cilia of the semicircular canals project?
Into the gelatinous cupula
What is the relevance of all the kinocili in the semicircular canals being orientated in the same direction?
Means they are all excited or inhibited together
What semicircular canals share planes?
Horizontal canals share plane with each other
Posterior canal shares plane with contralateral anterior canal
What do the semicircular canals form with their contralateral counterparts?
Push-pull pairs
What is the function of the otolith organs?
Sense linear acceleration and gravity
What are the otolith organs?
Saccule = movement in vertical plane Utricle = movement in horizontal plane
Where are the hair cells of the otolith organs located?
Within the macula = orientated in all directions
What are otoconia?
Crystals of calcium carbonate located on otolithic membrane
What is the function of the striola in the macula?
Divides hair cells into two populations with opposing polarities = allows for multidirectional sensitivity
What is the forebrain responsible for?
Perceived movement
What are the vestibular reflexes?
Vestibulo-ocular reflex = keeps eyes still in space when head moves
Vestibulo-colic reflex = keeps head still in space when you walk
Vestibulo-spinal reflex = adjusts posture for rapid changes in position
Why does alcohol cause loss of balance and dizziness?
Alcohol enters cupula which makes it less dense = floats in endolymph more
