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114 m a s s a g e & b o d y w o r k m a r c h / a p r i l 2 0 1 4 Working with the Vestibular System By Til Luchau Which way is up? It is such a simple question, but with such large implications. When you are upright, your body orients itself to gravity and to your surroundings, trying to keep your eyes and head level. This sense of "up" provides a point of reference for all balance, movement, posture, and position. An even more important question might be, "Which way is down?" Having a stable, trustworthy base of support is one of the body's prerequisites for a state of ease. Imagine trying to stand upright on top of a teetering stepladder—what happens in your body? Do you tighten, stiffen, or clench? This involuntary gripping reaction is triggered, to a greater or lesser extent, whenever your body senses instability or disrupted equilibrium. A neck affected by whiplash, an unstable ankle, or a painful sacrum are just a few examples of the many conditions that can throw off our body's fundamental sense of stability and orientation. Equilibrium is, of course, a whole-body phenomenon; for the purposes of simplicity, I'll focus in this column on the vestibular system, which is the single greatest contributor to your body's sense of balance. Together with the cochlea, which is the sense organ of hearing (Image 2), the vestibular system constitutes the labyrinth of the inner ear (Image 1). Arising from the ectoderm—the same embryonic layer that gives rise to the nervous system, eyes, and skin—the inner ear is the first sense organ to form in the embryo. By six to eight weeks after fertilization, an embryo has developed the inner ear's semicircular canals, making the sensation of movement our earliest sensory experience. The vestibular system detects head movement; the central nervous system then uses this information to coordinate body and eye motions. Through its remarkably geometrical arrangement of three interconnected, fluid-filled semicircular canals in each ear (Image 2), the vestibular system can detect movement in any of the three ordinal planes. technique MYOFASCIAL TECHNIQUES The labyrinth of the inner ear is embedded deep within the skull's temporal bone. It is comprised of the cochlea (purple), which perceives sound, and the fluid-filled canals (green), which sense movement. Image courtesy Primal Pictures, used by permission. The vestibular system detects two types of motion: rotational and linear. Rotational motions of the head (such as turning from side to side, tilting, looking up, or nodding) cause fluid in the semicircular canals to rush by specialized mechanoreceptors called the ampullary cupulae (Image 4, page 116), which are embedded with sensitive, hair-like cells (Image 5, page 116). Depending on which way they're bent by the fluid, these hair cells either open or close ion channels in their corresponding nerves, transducing the fluid's motion to a nerve impulse, which is processed in the brain. Linear motions, such as an elevator dropping or an airplane taking off, are detected by other hair cells elsewhere in the inner ear, which sense the inertia of embedded calcium carbonate crystals called otoliths (Image 5, page 116). One common form of persistent dizziness or vertigo (benign paroxysmal positional vertigo, or BPPV ) is thought to be caused by these otoliths (sometimes known as "ear stones") working free and tumbling to parts of the semicircular canals where they are not usually found. This overstimulates the hair cells in 1