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NESC 2570 > Mechanotransduction > Flashcards

Flashcards in Mechanotransduction Deck (23)
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Middle ear

-ossicles: malleas, incus, and stapes are the smallest bones in the body
-muscles: dampen the vibration of ossicles during loud noises, speech, and chewing


Physical amplification in middle ear

-ossicles concentrate the vibration on a smaller surface area which increases the pressure per unit area by 17x
-ossicles also act as levers (amplify by 1.3X


Inner ear

-longitudinal waves in the air make the oval window move in and out
-causes transverse waves in basilar membrane
-a particular region of the basilar membrane flexes back and forth in response to sound of a particular frequency


Von bekesy: physics of the basilar membrane

-base: narrow and stuff - vibrated to high frequncies
-apex: wide and floppy - vibrates to low frequencies


Hair cells

-cells where transduction occurs
-different hair cells maximally activated by different frequencies)
-stereocilia on hair cells deflected by tectorial membrane
-kinocilium thought to direct growth of stereocilia along a uniform axis
-if kinocilium is absent, stereocilia can form facing the wrong direction or may not be polarized
-in some species the kinocilium retracts later in development


Tip links and hcMET channels

-tip links: (cadherin 23 or protocadherin 15)
-connect stereocilia to eachother
-upon cilia deflection, change in tension on hair cell hcMET channels (hair cell mechanoelectrical transduction)


Transduction in hair cells

-ultra low latency depolarization upon hair cell deflection
-at rest, hcMET gates are partially open
-deflection of cilia toward long side open hcMET
-deflection of cilia toward short side closes hcMET
-K+ and Ca2+ enter hair cells through hcMET causing depolarization
-to pure tones (sine waves)<3000Hz, hair cells oscillate between depolarization and hyperpolarization (AC)
-another source of frequency information
-at higher frequencies (>3000Hz) oscillations blue together into depolarization (DC)


K+ flow in hair cells

-fast cycling between depolarization and hyperpolarization led to specialization in hair cells
-K+ mediate both hyperpolarization and depolarization
-hair cells K+ gradient mostly maintained by passive ion flow
-accomplished by having 2 different extracellular environments for different parts of the hair cell

-scala media: filled with endolymph (K+ rich/Na+ poor)
-reticular lamina: tight junctions - no ion exchange
-basal part of hair cells: bathed in perilymph (Na+ rich/K+ poor)

-stria vascularis enriches scala media with K+


Division of labor in cochlea

-inner hair cells carry sound information
-outer hair cells provide cochlear amplifier
-deflection of the cilia + central feedback
-upon depolarization, Prestin unbinds Cl- and contracts
-sharpen and amplify basilar membrane oscillations


Vestibular hair cells

-hair cells located in macula of saccule and utricle, and ampullae of semicircular canals
-works same way as hair cells in cochlea but mature vestibular hair cells still have kinocilium


-otolith organs

-heavy otoconia resting on squishy otolithic membrane - shear and sway
-gravity causes membrane to shift relative to hair cells in macula
-oriented hair cells:
1. Utricle: senses translation in horizontal place and sideways head tilts
2. Saccule: senses translation in vertical plane and up/down head tilts


Semicircular canals

-inertia causes endolymph lag behind head movement
-causes distortion of floppy cupula and displacement of embedded hair cell cilia


Somatosensory afferents

-cell bodies located in dorsal root ganglia
-long afferent fibres transit information from the skin to spinal chord
-called pseudounipolar: AP propagation need not pass through soma
-receptor endings of mechanoreceptors often surrounded by specialized structures


Mechanotransduction of touch

-stretching/deformation of membrane allows actions to enter a depolarize the afferent fibre
-many mechanoreceptors thought to express piezo2 channels (pressure channels)


Function of touch receptors

-each type of touch receptor has evolved to detect some behaviourally relevant touch stimulus
-response properties of each receptor are dictated by
-physical structure of receptor ending
-ion channels on unmyelinated ends of afferent fibres
-location of receptor


Merkel receptors

-continuous (slow adapting) response
-slow pushing response
-perceives fine details
-shallow location (tips of primary epidermal ridges)
-small (2-5mm)


Meissner receptors

-respond to change (rapid adapting response)
-perceives flutter, micro slip, hand-grip control
-shallow location (tips of dermal papillae)
-small (3-5mm)


Ruffini receptors

-continuous (slow adapting) response
-perceives stretching
-deep location (mid dermis)
-large (10-30mm)


Pacinian receptors

-response to change (rapid adapting response)
-rapid vibration of upper range
-perceives vibration and texture by moving fingers
-located deep (subcutaneous fat)
-large (entire finger or whole hand)


Mechanoreceptors for propioception 1.

-muscle spindles:
-sensory fibres coiled around intrafusal muscle fibres sheathed in connective tissue (tension distorts afferent endings to activate mechanoreceptors)
-group 1a: rapidly adapting, and give info about limb movement
-group 2: sustained responses, static limb position
-Y (gamma) neurons: cause intrafusal muscle fibres to contract
-adjust tension and sensitivity of spindle sensor

-Golgi tendon organ:
-group 1b sensory afferent woven throughout the collagen fibres that form tendons
-tension distorts afferent ending to activate mechanoreceptors



-AB fibres that conduct touch info are not involved in pain transmission
-responses to mechanical or thermal stimuli saturate in the range where stimuli would be perceived as painful
-nociceptors being to activate in this painful range


Nociceptive ion channels

-variety of painful stimuli (mechanical, thermal, chemical)
-nociceptive fibres lack the specialized endings like touch receptors
-called free nerve endings (unmyelinated)
-express various ion channels sensitive to painful stimuli
-many free nerve endings act as polymodal nociceptors (responsive to several types of painful stimuli)


Transient Receptor potential Channels

-TRP channels comprise a large family of cation channels that are activated by painful stimuli
-4 subunits with 6 Transmembrane domains each

-free nerve endings that act as a polymodal nociceptors presumably express multiple types of TRP channels to detect various form of painful stimuli

-TRPM8 detects cold and menthol
-TRPV1 detects heat and capsaicin