Skeletal muscles, then. The ones we have control over. Some, we don't. Arteries, for example, are wrapped in muscle. Aside from caked on, um, sewage, that's how they tighten up, so we can enjoy high blood pressure. We control arteries only to the degree that we control our emotions. Hardly at all.
Let's get a little technical. There are those big clumps of muscle, say, your calf. Like a bundle of cable, wrapped up in a connective tissue called the epimysium, which fades, transitions, into tendon, the function of which is just to tie muscle to bone ... Achilles tendon. The epi-casing is filled with cords that are wrapped, caulked, in perimysium. And inside these cords are actual muscle-cells bundles, wrapped in endomysium. See? Epi is ON the muscle, peri is ABOUT the muscle, and endo is IN the muscle. Three kinds of connective tissue, on a descending scale: epi, peri and endo.
So that's one sort of organization. The big (epimysium-covered) muscle bundle holds some number of (endomysium-covered) cords, each called a fasciculus. Fasciniculating, isn't it. And the fasciculus is full of muscle fibers, the actual cells, that do the work. Cords have threads, fasciculi have fibers. At last, we're there.
Muscle fibers, cells, don't multiply. So it is generally thought. We don't get more of them, when we do the Arnold thing. Instead, inside each fiber are some number of myofibrils. That's not hard to remember, is it? Fibers have myofibrils. Sometimes thousands. Depends. Did you exercise? Then you'll have more myofibriLs. This is where the change occurs. Myofibils are just long strings of proteins, which do the actual work, the contracting, moving, the heavy lifting.
This is where it gets really interesting. All this other stuff is just the alphabet. How do muscles actually move? Well, first, a muscle only contracts. It only pulls. That's its function. The biceps, arm muscle, pulls the wrist to the shoulder. You'd be stuck there forever, or just flop around, except that you have an opposing muscle on the back of the arm, an antagonist that pulls the wrist back, straightens out the arm. Triceps works in cooperative opposition to biceps. Easy. It's like that with all the skeletal muscles. There is no pushing. There's only pulling in a different direction.
But how does it happen, this pulling, this contracting? Observe.
Helpful? Here's how it works (we think). The red part in the illustration, inside, represents filaments of myosin, a protein. Think of the little balloons as waving around like random seaweed. When a spark is sent from a nerve, across the synaptic gap into a muscle receptor, it causes the muscle cell to release calcium ions out of storage and into the cell fluid, sarcoplasm. Calcium acts as a key, which fits into a protein lock (troponin), which opens a protein door (tropomyosin) located all over the blue strands, outside in the illustration. The red is myosin, the blue is actin. My Act. So the doors are open on the actin: Action!Those floating myosin balloons plug into the actin holes, and pull, right-side pulling left, left-side pulling right, toward the center. How do they pull? Electricity. You know, magnetism. Attraction and repulsion. Positive and negative poles. That's what ions are all about -- unbalanced electricity trying to get balanced. We're magnet operated, like something magical invented by Tesla.
Now it's a sort of bucket brigade tug-of-war, where two actin tubes slide along a myosin rod, toward the middle. The rods are free-floating, independent, contained as it were in the tubes. The tubes of actin however are hooked up end to end, all the way to the end of the cell, which is hooked up to the connective tissue, which is connected to the bone.
Once a myosin head, the balloon, has made its one wave, its pull, it unplugs from the actin, which has slid a tiny bit toward the center. Now that same head plugs into another receptor a tiny bit closer to the end. They do it out of sync, so it's not a one-two-three-heave sort of affair. Smooth.
There's more to it, of course. Like with sodium and its counterpart potassium. Together they generate an electrical impulse in a nerve cell that ends as the on-switch for muscle twitch. But all that's slightly outside our scope. It could go on forever.
Knowing this, we might ask -- in love as we are with excellence and superb physical performance -- how we can facilitate the process, at this ionic level. Can myofibrils learn? -- improve? Well, all they do is a sort of zipper slide. It must be about available energy, damage repair and maintenance. That's nutrition. The more calories you eat, the more free-radicals -- stray bullets -- are ricocheting around your DNA, doing damage. Like racing an engine in the red zone -- lots of pollution. So eat the minimum necessary. Then, providing nutrients -- that most minor of reasons to eat, way less important than tasty pleasure, or calories for energy. Or so it seems, for so many folks. All that calcium and potassium and, yes, even sodium -- you couldn't move without them. So have what is necessary.
That's diet. Exercise? Well, training makes you more fit. But how about at a cellular level? Can you train myofibrils? It seems that if you use a maximum contraction, have as many myosin heads engage as possible, plug all the actin receptors there are -- pull the zipper as far as it will go -- if you do that, there must be some training benefit. Some feedback mechanism that encourages and facilitates the process? Static holds of maximal weight send a terrifically powerful signal to the brain, but that's at the hormone end of the formula. Would using a maximal contraction have an analogous effect on the muscle fiber side of the equation? Tests of the theory suggest so. Ah well. We could go on. It's all so fascinating.
So that's how muscles work. But of course the real reason they work is that you decide to exercise, rather than sitting around watching soap operas and gaining a pound of fat each year until you die. That's the pattern. How sad. But we're better than that, or will be. We can't control everything, but we can control what we do. Sometimes we need a little help. With exercise, with diet, and with the really hard thing, motivation. So? Get help, if you need it. Because natural selection isn't impressed with civilization, and excuses don't work with the coroner.
Be excellent.
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