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Lecture

Lecture 4


Department
Biology
Course Code
BIO271H1
Professor
Ohana

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Lecture 4
Sensory Physiology: Mechanoreception
Mechanoreceptors
oCan be simple undifferentiated nerve endings, or
oCan be complex, like the Pacinian corpuscle
oMechanoreceptors also include stretch receptors in the skin, and
the auditory and vestibular structures of the vertebrate ear
oMechanoreceptors are activated by a stretch or distortion of
their plasma membrane
oTransduce mechanical stimuli into electrical signals
oAll organisms (and most cells) sense and respond to mechanical
stimuli
oWhy do we need mechanoreception?
oTwo main types of mechanoreceptor proteins:
ENaC
Epithelial sodium channels
TRP chanels
Transient receptor potential channels
oMechanosensory Protein Receptors
Channels are linked to extracellular matrix and to the
cytoskeleton
Mechanical stimuli cause the extracellular anchors to
move relative to the cytoskelton, pulling on the channel
and causing a conformational change that opens and
closes the channel
Touch and Pressure
oProprioreceptors (monitor body position)
oBaroreceptors (detect pressure changes)
oTactile receptors
Receptors that detect touch, pressure, and vibration
Widely dispersed in skin
Receptor structure:
Some are free nerve endings
In some the nerve endings are enclosed in
accessory structures
Eg. Pacinian corpuscle
Free Nerve Endings and Merkels Disks
oMerkels Disks are free nerve endings associated with an
enlarged epidermal cell
oUsed for fine tactile discrimination
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oSmall receptive fields
oSlowly adapting tonic receptors most sensitive to indentation of
the skin
Root Hair Plexus
oRoot hair plexus are wrapped around the base of the hair
follicles and monitor movements across the body surface
oRapidly adapting phasic receptors; sensitive to changes in
movement
oRapid adaptation by the Pacinian Corpuscle is a good example of
mechanical filtering by accessory structures
oThe Pacinian Corpuscle is a pressure and vibration receptor
found in the skin, muscle, tendons and joints
oWith the corpuscle intact the neuron depolarized transiently at
the onset and offset of the stimulus
oWith the accessory layers removed the neuron remained
depolarized during most of the stimulus
oHow do accessory layers produce sensory adaptation?
o*Slide 14 in lecture notes
oThe layers of the corpuscle preferentially pass on rapid changes
in pressure while filtering out prolonged steady pressure
oThis explains in part why we quickly stop noticing moderate
sustained pressure such as the stimuli that wearing clothes
produces
Vertebrate Proprioceptors
oMonitor the position of the body
oTypically do not adapt to stimuli
oThree major groups
Muscle spindles
Located in skeletal muscles
Monitor muscle length
Golgi tendon organs
Located in tendons
Monitor tendon tension
Joint capsule receptors
Located in capsules that enclose joints
Monitor pressure, tension, and movement
Insect Tactile Receptors
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