This entry will shed light on the third essential component of postural control – the visual system. I won’t talk about the interpretation of visual information in the brain but a little bit on how the eyes and spine work as a unit.
The Visual System:
Our eyes provide visual information about our environment. This information is used for various purposes such as focusing on a new target in our visual field, e.g. a threat we have to pay attention to or provide us with a stable reference point for stability.
The spine, the vestibular system and the visual system function as a unit. A good way of demonstrating some of these linkages is to position the index and the middle finger of both hand over the muscles just beneath the back of your skull, and while keeping the head still look towards left and then right. You should be able to feel the muscles at the back of your head contract. Another example that we’ve all experienced is the one while sitting in the train with another train just outside the window. When the other train starts to move you might feel as if you’re moving although the one you’re sitting in remains stationary. In both of these cases the visual information and fixation/movement of our eyes to a new target will be interpreted as movement due to the shared connections between the three aspects of balance and posture that we’ve been talking about in the previous entries.
These shared primitive reflexes between the spinal muscles, the vestibular system and the visual system allow activation and appropriate adjustments to protective/stabilizing motor function whenever necessary e.g. in case of sudden loss of balance (contraction of skeletal muscle to maintain stability) or arising from a seated position (contraction of muscles in the blood vessel walls to maintain appropriate blood pressure to avoid blackout).
Consider slippery, smooth tiling on the pavement after the rain. As you walk along unprepared for slippery surface the subconscious calibration of appropriate stabilising muscle responses are challenged by sudden change in the characteristics of the terrain.
*A little sidetrack here is appropriate: the reason I mentioned the subconscious calibration is that the stabilisation of our musculoskeletal system depends largely on the subconscious expectations we constantly make about our environment (just like walking up/down the stairs and remembering the last step wrong can, in a worst case scenario trigger spinal pain or headaches). What your body does in order to keep you upright depends on the expectations on what is to come and how to respond to these expectations. If these expectations are not met, sudden and fast adjustments to muscle function have to be made in order to maintain/regain balance.*
Now, once you step on the slippery tiling and start to lose balance this change in momentum and body position is picked up by the joint position sense receptors in the muscles and the change in direction of fluid flow in the vestibular system. Your eyes will then try to fixate themselves in the horizon so that a stable reference point can be obtained for trying to stabilize the skeletal system as it’s balance is momentarily challenged. All of this happens in the matter of milliseconds without you having to consciously think about what to do – your body will react to this on its own based on the integrity and functionality of these primitive reflex connections.
Next time I’ll be steering away from this “neurological mumbo jumbo” and discuss how all this is linked to the common conditions we see every day and why people experience not only “unexplained” spinal pain but a raft of other symptoms as well. Chiropractic care can provide tremendous relief to these common problems – no magical voodoo tricks here, just an understanding of the underlying principles of human function and appropriate therapeutic applications for intervention.