A HYPOTHETICAL MODEL
Barrett L. Dorko, P.T.
thousands of times I have listened to my patients
report a variety of sensations arising some distance from the
placement of my hands. I am no longer surprised at the report of
these sensations, their variety, or their location. Not only do
they commonly occur within a dermatome totally unrelated to the
skin I'm touching, but often cross the mid-line and can be felt
as far from the contact as you could possibly get. Several
different sensations in as many locations may also be felt.
The following is a brief explanation and interpretation of some research which may help to explain this.
The translation of mechanical deformation in various tissues to an electrical signal strong enough to be sensed and properly interpreted by the brain has been explained several different ways.
Sensation of any sort requires a difference in net charge across the neuronal membrane that exceeds its normal resting potential. Achieving this state normally requires the influx of sodium or calcium through "ion channels": cylinder-shaped protein molecules, that permit chemical diffusion to occur without energy expenditure. When enough channels open, depolarization occurs and the experience of sensation is then possible.
It has been known that ion channels may be ligand (chemical) or voltage (electrical) gated. Recently, ion channels that are activated via increased membrane tension have been discovered in many tissues. Mechanically sensitive tissues throughout the body possess stretch-activated (SA) ion channels capable of immediately responding to deformation of the tubes, rods, and strings that form the matrix of the cytoskeleton. These channels account for the propagation of sensation secondary to movement (proprioception) or internal stress (interoception).
Altering the SA ion channels in various sequences will eventually produce voltage gated ion propagation which is very much like lighting a fuse, sending a quick message to the brain via the inter-neurons. The resting membrane tension of the cytoskeleton is directly related to the ease with which mechanical deformation may recruit enough SA ion channels necessary to eventually promote nervous depolarization. The higher the resting tension, the easier it is to open a sufficient number of channels.
If the resting tension in the epithelium and its intimately associated connective tissue is higher than normal, a chain reaction of channel opening will be facilitated. This is ultimately displayed by a report of sensation that knows no neurologic boundary. The absence of a typical dermatologic reference is due to the fact that numerous tissues unrelated to nervous tissue posses SA channels. They may serve as a bridge from one dermatome to the next mediated by mechanical deformation of the connective tissue between nerves.
If distant sensation and change is common with "Simple Contact," (the name of my technique) it would be reasonable to assume or propose the following:
- The absence of distant sensation with provocative contact is
due to the inevitable muscle guarding elicited with that type of
handling. This effectively sets up a barrier that will not allow
the domino-like effect to spread.
the potential effect of simple contact in this
way allows the therapist to appreciate how sensation and change
in our patients can occur with remarkable variety and speed.
Relinquishing the agenda usually present with manual care and
choosing to be a companion to the patient and their unique
processes reveals the intelligence and corrective power every
person possess. This attitude arises from an understanding of the
materials we handle, and if we deform the skin without a distinct
knowledge of what happens next, and why, the potential for
distant and profound change is lost.
"The Intimate Sense; Understanding the Mechanics of Touch" by Frederick Sachs. "The Science" Jan/Feb., 1988 Published by The New York Academy of Sciences, Two East Sixty-Third Street, New York, NY 10021
"Baroreceptor Mechanisms at the Cellular Level" Frederick Sachs; 1986 Update In Cardiovascular Neurobiology; Federation Proceedings Vol. 46 No. 2 January 1987
"Mechanotransducer Ion Channels in Chick Skeletal Muscle: The Effects of Extracellular Ph" Guharay and Sacks Journal of Physiology (1985) 363 pp. 119-134.
"Single-Channel Currents from Acetylcholine Receptors in Embryonic Chick Muscle" Averback and Sachs, Biophysics Journal Vol. 45, Jan.l984
"Stretch-Activated Single Ion Channel Currents in Tissue-Cultured Embryonic Chick Skeletal Muscle" Guharay and Sachs Journal of Physiology (1984) 352 pp. 685-701