Mechanisms for Hypertonicity
By Thomas Griner (published article Dynamic Chiropractic)
Hypertonicity is enacted by reflex overstimulation of the alpha motor nerves. Four main reflex responses can be involved. Three of these reflexes tend to be temporary and varied in nature, and are referred to as dynamic reflexes.
These include the:
- myotatic stretch reflex;
- guarding reflex (pain driven);
- splinting reflex (pain driven);
- internal organ reflex (insensate to sensate).
The fourth reflex is a static reflex in that it is constant and unvarying, so the dynamic reflexes may add to this from time to time. The reason this maltonicity is static is that it is a disturbance of the mechanism that controls normal static muscle tone. Lactic acid, concentrated to a toxic leve,l disturbs the feedback to the cerebellum, which sets normal tone. The resulting overstimulation is thus more complex than simple reflex. The induced hypertonicity then creates a vicious cycle (positive feedback) by maintaining or even increasing the pool of toxic-level lactic acid.
By this same process, whenever one of the dynamic reflexes induces temporary hypertonicity, some toxic-level lactic acid is trapped. This leaves a residual static reflex overstimulation, which accumulates with each episode.
Another vicious cycle can be created by the internal organ reflex. The neural connection to the superficial muscle, which the insensate organ utilizes to trigger conscious awareness, appears to be a two-way street. When that superficial muscle becomes irritable from hypertonicity, it agitates the coupled internal organ.
The dynamic reflexes are simple spinal reflexes, so anything that can block their ability to stimulate the motor nerve can reduce the muscle reaction. So-called muscle relaxants act as indiscriminant spinal blockers. This helps explain some side-effects of such drugs. Hypertonicity in deep muscles excites the Renshaw inhibitory nerves, which also act to block the superficial reflex response without the usual drug side-effects, but with the usual effects of this form of tension
The "chill" is another dynamic reflex which can cause temporary hypertonicity. Although it is much milder than the other three reflexes, if it occurs in an area that is already heavily involved in muscular tensity, it can act as the "straw that breaks the camel's back." This is particularly true of people who allow their washed hair to air dry, which chills the infamous suboccipital muscles.