mechanoreceptors one Flashcards
nerve endings in glabrous skin
merkel cells
ruffini endings
pacinian’s’ corpuscle
meissner corpuscle
free nerve endings
what do nerve endings that terminate in your skin cause?
cause you to have tactile experiences
how did scientists identify somatosensory nervous system in c elegans
lesioned neurons one by one
after some lesions, the worm wouldn’t swim away, so it was concluded that these were neurons involved in somatosensation
O’Hagan et al (2004)
recording from neuron PLM, immobilised on microscope slide
- intracellular electrophysiology, record membrane potential of a specific neuron
- green fluorescent protein labelling of PLM cell, so we can see where to record from under fluorescent microscope
1) record from the cell
2) carefully touch the animal
3) response, receptor potential, ion channels open, sodium current
human mechano-transduction
what we knew and mechanism concluded
- Response happens very quickly, therefore it cannot be a signalling cascade
- Mechanical force acts directly to stretch membrane and open ion channels
Mechanism of touch signal transduction appears to be direct deformation of cell membrane
coste et al (2010)
whole cell electrophysiology
screen cell lines poke assay
mechanically activated current
cell on a dish, poke the cell, can record if there is any change in membrane potential when you poke the cell
found a cell line that does mechanoreception, it is helpful to study genetic mechanisms
must be one or more proteins expressed in the cell that are key players in mechanotransduction
- DNA micro array
- Small interfering RNA (siRNA) knock-down
- Trying to find Piezol
tells you thousands of genes expressed in this cell
concluded it was meant to be a membrane spanning protein, bringing it down to a list o 75 candidates
inactivated proteins and repeated poke array technique, if they inhibit the protein involved, no receptor current would be produced
where was piezo 1 found?
mainly in internal organs, not the skin
ow was piezo 2 found?
When searching trough DNA database, they found structurally similar protein to piezo 1 that was expressed in the skin
how was it shown that piezo 2 is necessary and sufficient for mechanotransduction
if you express piezo 2 in a cell that doesn’t already express it, that cell should be able to produce mechanical receptor potentials
-found in cell lines, sufficient
If you have an animal where you inactivate it completely, they should become less or insensitive to touch
-completed poke rest on knockout mice (behavioural test)
-Piezo 2 is essential for mechano-transduction
somas of mechanoreceptors:
body: dorsal root ganglion
face: trigeminal ganglion
DRG/TRG axon:
primary afferent fibre
peripheral branch (to extremities)
central branch (to the brain)
thin/ unmyelinated primary afferent fibre
axons related to our sense of pain
mechanical force has rapid effect, but tissue injury travels slowly to the brain
thick/myelinated primary afferents
action potentials propagate more quickly, so APs go faster to CNS
Adrian and Zotterman (1926)
- insert electrode into part of nervous system you are interested in, electrode becomes sensitive to ions flowing across membrane, can measure action potential
- can study the function of the neuron to see what it is sensitive to
- discovered many types of primary afferent
