(583 posts)
Oct 21, 2010 8:40 am
tactile invisibility -- gamma loops --
I asked for an explination of gamma loops on face book George Spriggs wrote me back :
Need to know two things: Gamma efferent fiber and muscle spindle. GEF (motor nerve fibers) that send impulses from Central nervous system (CNS) to muscle spindles. GEF responsible for deep tendon reflexs, spasticity, and rigidity...not for degree of contractile response. They help regulate the sensitivity of the MS and the total tension of the muscle. The MS are a proprioceptive sensory organs that are triggered by the GEF. Innervation is the stimulation of a muscle by a nerve. Muscles that provide force have large innervation ratios (legs/trunk) and those that provide fine manipulative functions have smaller innervation ratios (hand/face). The smaller the ratio the more precise the control. My understanding of the phenomena you just share is this. If you simply move smooth enough that a person cannot detect what position of off balance they are in via the limb you control, they will be unable to provide a sufficient recovery response to you because (1) They do not realize where they are or where they were moved by you (loss of proprioception) and (2) once the brain realizes it, the way the body works to get the force it needs causes it to act spastically because the only muscles that can truly respond are the large groups because of the larger innervation ratios, but that leads to them assisting in their fall because the movements are spastic and not refined. Good example is the effect of shomenate: Hand hits chin and forces cervical spinlock. The solution is sacral lumbar innervation to relieve the cervical lock, but ultimately winds up in lumbar sacral spine lock. The remedy to that is the metatarsal kick to relieve the LS spine lock. The kick is so strong that it launchs a person off he ground as if they were skating and slipping on ice. The resultant is feet going skyward while the rest of the body remains in its original position. What we have learned to do is to allow the metatarsal kick, but our proprioception and fine motor skills kick in and we are able to manage a finely controlled squat to a rolling/sitting fall. In this instance, you got to see how the large and small innervated structures work. Essentially, those who really understand anatomy and physiology are able to develop strategies for off-balancing uke because they understand the effect of subtle actions on the body. What your folks introduced was not magic, but an acute understanding of the break-down between the muscles that provide gross functions, the muscles that provide fine functions, and the point where proprioception is lost between the two. I hope I kept that simple