Nociception Flashcards
The cell bodies of afferent neurons which contribute to the reflex arc are located in…
The dorsal root ganglion
Majority of the nociceptors in the skin are this kind of receptor
Free nerve endings
Which kinds of nerve fibres are involved in nociception (2)
A-delta and C
Which kind of nerve fibres are involved in “fast” pain
A-delta
Which kind of nerve fibres are involved in “slow” pain
C
Describe the morphology of A-delta fibres
Myelinated
Describe the morphology of C fibres
Unmyelinated, small diameter
What are “silent” nociceptors, what kind of fibre are they made of?
Nociceptors which only develop sensitivity after injury (e.g. when u poke a bruise)
What is the most innervated tissue in the body with respect to nociception?
The eye
Within the eye, which is the most innervated tissue wrt nociception?
The cornea
Describe the % makeup of the nociceptive fibers in the cornea
30% A-delta
70% C-type
What is the life expectancy for someone who does not have a sense of pain?
Less than 25 years
What are the 3 modes of nociception?
Thermal
Mechanical
Chemical
What are the channels involved in chemical nociception?
ENaC
What are the main channel associated with many modes of nociception, but primarily thermal nociception?
TRP
What are the channels associated with mechanical nociception?
KNCK (stretch-sensitive K channels)
Piezo
What is the channel associated with capsaicin nociception?
TRPV1
Why does capsaicin on the skin lead to a burning sensation?
Because we have TRPV1 receptors in our skin
The TRPV1 channel is activated by… (2)
Noxious heat (thermal)
Capsaicin (chemical)
How can capsaicin be used as an analgesic?
Capsaicin induces long lasting desensitization of nociceptive fibers - could use this to our advantage to desensitize nerve fibers in arthritis, for example
What is the channel activated by menthol?
TRPM8
What is the cell which makes up majority of the epidermis?
Keratinocytes
How are keratinocytes involved in nociception?
Under mechanical pressure, they will release ATP which can stimulate surrounding cells, including free nerve endings
What is TRPV3?
Heat-sensitive TRP channel expressed in keratinocytes
What chemical compound can activate TRPV3 channels?
Camphor (found in tiger balm)
What sensation is experienced when TRPV3 is activated?
Warming
When keratinocytes have knockout TRPV3, what happens to their camphor sensitivity?
Become insensitive to camphor
Why is it significant scientifically that TRPV3 are not expressed in DRG?
Breaks down the idea that peripheral sensory detection is mediated solely by DRG, which was previously believed
