Triad of Equilibrium

One of the most important activities of the brain-body system is keeping track of where the head is in space. The visual, vestibular and somatosensory systems interact together as a “Triad of Equilibrium” to monitor the position of the head and cervical spine.

The brain is encased in a durable shell at the top of the axial system, surrounded by powerful sensory receptors. The contribution of some of these sensors – the special senses of the eyes and ears – is well acknowledged. But more mysterious and rich in potential for the chiropractor-biomechanic, are the “proximal senses” – the vestibulo-proprioceptive system. Our ability to safely and efficiently interact with our environment requires:

  1. sensory input from the visual, vestibular and somatosensory systems
  2. integration of that sensory input into meaningful, reliable data
  3. accurate motor output to achieve our desired action.

Somatosensory feedback for balance and postural control of the head comes from richly innervated neck muscles. For stabilization of the head some of the most proprioceptively significant neck muscles seem to be the small rectus capitii found at the base of the skull. These 6 pairs of muscles are highly innervated and seem to have a top down influence on the stability of the whole biomechanical system.

rectus capitiiThe rectus capitii are short, and loaded with proprioceptors. Individually and as a group they are fan shaped and their spindle cells are more densely packed and evenly spread out in the ray. (Most muscles have the spindle cells in the belly of the muscle.) This unusual arrangement allows the brain to get accurate information about the activity of the muscle, allowing more precise tracking of where the head is in space. The cerebellum is a “comparometer” but also predicts future position and anticipates direction. The fan shape of the rectus capitii and the rate of transition from one muscle to the next allows the cerebellum not only to know where the head is at the moment but also to predict future movement, where the head is going and where it will be next. This allows for exquisitely precise corrective and anticipatory adjustments in head position.

In most people three of the muscle pairs have direct attachments to the meningeal dura itself (rectus capitus posterior minor, and another slip of muscle from rectus capitus posterior major and obliquus inferior) and may be strongly implicated in cervico-genic headaches and other cranial-meningeal problems. They initiate and guide movement of the head and most injury to the head/neck will result in confusion – over facilitation or under facilitation – in some or all of these muscles. Additionally, chronic anterior head carriage shortens these muscles and over time can cause congestion of cerebral spinal fluid and lymphatic flow. In our experience, Axial Stability Method® seems to reduce stress on these muscles with laser specificity and allows the body to reorganize, and balance the muscles.

Correcting “laterals” chiropractically seems to strongly affect many systems. The stability of the upper cervical spine cannot be undervalued. It seems to involve all of the following layers of the brain-body system: structure, muscle, dura, vestibular system (via the cerebellum), the visual system (focus-peripheral and the vestibular ocular reflex (VOR), and energetic and immune systems.