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NS9 - Sensory Rs + Pathways (ii) (Primary Sensory Afferents (highly…
NS9 - Sensory Rs + Pathways (ii)
Stimulus strength
strong stimulus - large generator potential - high frequency APs
weak simulus - small generator potential - low frequency APs
Lateral Inhibiton
= capacity of an excited neuron to decrease activity of its neighbours
2-point Discrimination
= ability to discern that 2 objects are touching the skin at 2 nearby but different points
occurs when neurons don't converge
Stimulus threshold
= min amount of stimulus that has to be there in order for it to be detectable
Stimulus intensity is encoded in 3 ways...
1) No. of activated Rs
2) degree of different in sensory neuron firing state
3) No. of activated R types
impulse patterns + duration also matter
Phasic Rs
Fire when stimulated @ first, but adapt (cease firing) to a constant stimulus that isn't viewed as a threat
allows brain to focus on important info
e.g. olfactory Rs, Pacinian corpuscles
Tonic Rs
never adapt to constant stimulus because stimulus must be monitored @ all times (e.g. BP, pain)
always fired as long as threshold is reached
e.g. nociceptors, baroRs, Merkels discs
Dermatome
= area of skin from which all sensory fibres enter 1 given spinal root
Primary Sensory Afferents
sensory neurons in PNS
transduce info about mechanical, thermal + chemical states + transit it to CNS
highly specialised
1 type of R to 1 part of cortex
cell body in doral root ganglion
axon spits in 2
connects with sensory R @ one end, connects with dorsal horn of cord @ other
Neuron polarity
multipolar
dendrites come out of soma
heavily myelinated (lots of Schwann cells)
bipolar
soma in middle of process
unipolar
soma in ganglion
A alpha + beta fibres
heavily myelinated (fast conducting)
proprioception, vibration + discriminative touch travel through these
A + C fibres
thinly myelinated/ unmyelinated (moderate/slow conducting)
pain + temp travel through these