Development of Touch and Nociception Flashcards
what triggers a sense of touch generally
mechanoreceptors - they are depolarised by a mechanical force on the skin which generates an AP
what are the 4 types of mechanoreceptors?
merkel, meissner, ruffini, pacinian
what do merkel receptors detect?
- pressure
what do meissner receptors detect?
flutter
what do ruffini receptors detect?
stretching
what do pacinian receptors detect?
vibration
are the receptors which detect touch the same as those that detect pain?
no- nociception
what stimulates nociceptors generally?
mechanical, heat, cold, chemical
do nociciceptors have specialized anatomically recognisable endings?
no- all the same generally when you look at them
what detemines the sensory neuron function of the nociceptors?
the specialized transduction channels
what channel is associated with touch reception?
MS (low threshold)
what channel is associated with painful reception?
TRPA1, TRPV1,2, MS (high threshold) and ASICS
where are all of the cell bodies of sensory neurons?
in the DRG
where do the sensory neurons synapse?
at the CNS in the dorsal horn of the spinal cord
describe an experiment which looks at the timing of sensory reflex arc development. what did they find?
- take the pup fetus from the mother
- at different stages in development
- 21 days is when the pups are born
- the scientists touched different parts of the body and asked if you could get a reflex movement from different parts of the body
- they found that at 16 days there was very little response
- at 17 days there seemed to be more response- more response in the upper part than in the lower.
- not until the 20th day is the reflex arc formed to the same extent in the caudal region
where do mechanoreceptors and nociceptors arise from?
- the neural crest
- can see these cells migrates around E9
- the NC migrate around E9 and then within 7 days they become an entire set of sensory neurons and innervate the skin etc
how is the size of the sensory neurons in the dorsal root ganglion related to their function?
- the large cells (A cells) are the mechanoceptors: touch. They are also the proproceptors that are used for position sense
- the small cells (C cells): nociceptors for pain and thermoreceptors for temperature
at E12 what has happened ?
the cell bodies of the sensoty neurons are in the DRG but they have differentiated in terms of size
what are the genes that are important for neuron specification?
there are certain geens which are expressed- neurogenin 1 is required for sensory neurons and neurogenin 2 is required for nociceptor development
what are the general (non geentic) waves of sensory neuron specification? what does this say about development?
- at E9.5 it begins. The premigratory NC. the decision that these NCs will become sensory is made before the cells have reached the DRG: they are sensory neuron commited. This is true of the mechanoceptors but the nociceptors stay multipotent for longer and only become committed after migration at around 10.5-11.5 . this shows that the commitment of mechano is in advance of nociceptors. you may want the nocicceptors to come first because they will keep animals alive but you could also say that the ability of the young to bond with its mother which requires mechano is more important and maybe if you are attacked as a lion as a new born, what would be the point of having nocicpetors because you cant do anything about it.
when isn nrg-1 critical?
it is required for the commitment of the nociceptors durin the post migratory stage of nociceptor commitment
when is neurogenin 2 critical?
it is critical during the migratory stage of the sensory mechanoceptors in order to specify them as mechanoceptors
what are the runx genes?
- they are important at arond E10.5- when the two groups of noci and mechan have divided and you want to make sub groups
what is the role of runx3?
it is involved in determinng whether the pre commited mech (no or low runx3) or prop cells (runx3)will become mechanoreceptors or sensory receptors (will they be in the tactile in the skin or proprio in the muscle spindles)
what i runx1 involved in?
determining which on the nociceptors will express peptidergic neurons (no runx1) or non peptidergic (runx1)
what is the role of pptidergic vs non peptidnergicneurons ?
??