KIN 313 Lecture 14: Proprioception and Kinaesthesis 2

Which skin receptors help with position sense and why

SA2 (ruffini): detects skin stretch

FA1 (meissner): motion detection

How do SA2 and FA1s provide position sense

SA2 tells you joint/finger position due to coding for skin stretch (large receptive field = don’t know exactly which thing is moving)

FA1 tells you which joint/finger is doing that (small receptive field = specific location) → picks up the transient and codes for velocity of skin movement → fires more rarely, only when joint is actively moving

Cutaneous input causing illusions

• numb the finger down from a certain point above a joint

• participants can still tell when you bend the joint bc it stretches the skin proximal to the block

• or, bend the joint but stretch/slacken the skin in a way that would mean it was bend in the other way, and they think it is bent in the way that matches the skin stretch

• but everything proximal to the block worked, even the muscle spindles. The spindles would have been coding correctly, but the cutaneous feedback overrode them

• shows we depend on the code from FA1 and SA2 for position sense, potentially more than spindles?

problem with code from muscle spindles, how to solve

ambiguous nature

• firing rate might mean one length without gamma drive and another when you do have gamma drive

need to know what gamma drive you gave to the spindle so that you can make sense of what is coming back from the afferents

so you send a copy of the gamma drive (aka efference copy) to the sensory cortex. then when the gamma tunes the spindle and the spindle sends info up 1a to the sensory cortex, it can subtract the efference copy from the 1a code it received to get the absolute code