When you hear the word calcium probably your first thought is the health of the bones. No doubt calcium is a key component for strong bones, but its presence in your muscles allows movement. The contraction and relaxation of your muscles occurs due to rapidly changing calcium concentrations within the cells of your muscles, a biochemical process known as the calcium cycle. Having too much or too little calcium in your blood can cause muscle symptoms due to the interruption of the calcium cycle.
Anatomy of Muscle cells
To understand the calcium cycle you need to know a little about the anatomy of muscle cells. The fiber strands called myofilaments are the distinctive feature that separates muscle cells from other types of cells in your body. A muscle contraction represents the shortening of the myofilaments with the individual cells that make up the muscle. A tiny, tube-like network called sarcoplasmic reticulum, or RS, surrounds each myofilament. In a state of relaxation the RS contains a high concentration of calcium. The RS controls muscle contraction and relaxation by regulating the flow of calcium within the cells of your muscles.
The Calcium Cycle
Muscle contraction begins with an electrical signal to “activate” your brain. The signal stimulates the RS to open its calcium doors, flooding the myofilaments with said mineral. The sudden increase in calcium concentration causes a chain reaction of energy consumption that causes the myofilaments to change shape and shorten. The simultaneous shortening of thousands of microscopic myofilaments causes mucular contraction.
When the signal “activate” stops, the calcium gates of the RS are closed and the calcium pumps quickly return said mineral from the myofilaments to the interior of the RS. As the concentration of calcium around the myofilaments is reduced, your muscle returns to its state of relaxation.
Fast and Slow shrinking fibers
Your muscles contain different types of fibers, broadly categorized as fast or slow contraction. As the name implies, fast-twitch fibers contract and retract faster than slow-twitch fibers. However, your slow-twitch fibers have a greater resistance than fast-twitch fibers, as in the fable of the turtle and the hare. The RS in fast-twitch fibers is more developed than in slow-twitch fibers, allowing a faster release of calcium in response to an “activate” signal. Your muscles contain a mixture of fibers of fast and slow contraction, although one of the two predominates in each muscle.
A low level of calcium in the blood, or hypocalcemia, causes muscle irritability. With this condition you can experience muscle cramps in your back and legs. Spasms may also occur in your facial muscles. An abnormally high calcium level in the blood, or hypercalcemia, causes muscle weakness and slowness. Muscle symptoms usually do not occur with hypercalcemia unless your blood calcium level is critically high.