The range of muscular contraction (GB#115C03)
● Why do muscles in your arms bend your fingers?
Skeletal muscle basically bends and stretches the joint. Muscles of various sizes and lengths are stuck in the body. There are more than 600 muscles in the whole body, and it is much more than the number of bones and joints. Why such a muscle in such a place? There are many places to wonder. Especially when I first learned that most of the muscle moving the fingers of the hand was out of the elbow far away rather than by hand and there was only a tendon near the fingers for the first time, I was quite surprised.
- 1 ● Fingers beyond the length of the fingers
- 2 ● Muscles can not grow and shrink so much
- 3 ● The range of muscle stretching is proportional to the length of the muscle fibers
- 4 ● The rate of muscle contraction is also proportional to the length of the muscle fibers
- 5 ● Long muscle has longer the range of contraction than short muscle and faster contraction rate
- 6 ○ Referenced sites
- 7 ○ Related articles
- 8 ○ Referenced books
● Fingers beyond the length of the fingers
For example, the muscles that bend the index finger are the superflexi flexor muscle and the flexor flexor muscle, and the stretching muscle has total finger extensor muscles, but all come out from the lower end of the humerus above the elbow far from the finger. Where the flexor strikes the bone (origin) is the medial condyles of the humerus and the origin of the extensor is the lateral superior condyle of the humerus. The body of the muscle (muscle belly) is in the forearm, the part beyond the wrist passes through as a tendon and stops on the bones of the fingers. Why would you think that it is making such a roundabout?
Regarding the mechanism by which the skeletal muscle contracts, it has become clear that actin and myosin, which are the protagonists thereof, are working not only in the muscles but also in all cells. Research seems to be stepping into a terrible nano-level area like God. On the other hand, the description of the muscle contraction mechanism of textbooks is almost like 50 years ago and it does not shine. Certainly, the mechanism of sliding of actin and myosin and the mechanism of excitation contraction coupling are the main points of muscle contraction and isometric contraction and isotonic contraction are important, but it is not good to go ahead and talk a little more.
● Muscles can not grow and shrink so much
Although it is hardly emphasized in physiology textbooks, the surprisingly important point that is derived from the mechanism of skeletal muscle contraction is that the limited range of extension and contraction that can give power is quite small.Speaking of things that grow and shrink, rubber strings and springs come to mind. In such an image it is likely to double or triple the shrinkage, but the fibers of the skeletal muscle only grow to about 1.5 times at the most when shrunk most.
According to Juntendo University School of Medicine anatomist, Dr. Tateo Sakai, the growth and contraction is about 10%. This is a limitation that comes from the mechanism by which skeletal muscle contracts itself. Since the occurrence and shortening of muscle forces is generated by the sliding power of a certain length of myosin filaments at the nano level called myosin and actin constituting the sarcomere, the range of extension and contraction is at most twice the limit. Actually, since various structural restrictions are added, even if it is restricted to the original muscle fiber part, it is at most 1.5 times, and even if the part of the tendon not stretching and shrinking is included in “length of muscle”, its length The range of change will be only about 10%. If the stretch and contraction of the muscle is 10%, 10 cm of muscle is necessary to obtain 1 cm of elongation contraction width.
● The range of muscle stretching is proportional to the length of the muscle fibers
The range of expansion and contraction of one sarcomere is 1.5 times, that is, the change rate is 50%. The myofibrils in the muscle fibers are the sarcomeres connected in series. Even if you connect two sarcomeres in series, the change rate will remain at 50%. However, the distance of extension and contraction, that is, the range of contraction is doubled.Four skeletons are connected, in series, the range of contraction is twice that of the sarcasm. The range of extension and contraction is longer as the myofibrils are longer. That is, the longer the muscle fiber, the longer the range of contaction.
It seems that it is not fixed especially how to call this distance of extension and contraction. In this case, we use it to compare the reciprocating motion of the piston, the width of the expansion and contraction of the spring to the process, the stroke. But in English muscle contraction “power stroke” refers to the reciprocating motion of myosin’s head. Also, simply stroke is generally confusing because it will be a stroke of the brain. Then, “the range of contaciton” in this site (8/24/2018).
● The rate of muscle contraction is also proportional to the length of the muscle fibers
Even if there is only one sarcomere, if 10 loads are connected in series, if each load is the same, each sarcomere will contract at the same time. So the whole ten connected sarcomeres will contract at a rate 10 times faster than a single sarcomere. When comparing the fiber having four sarcomere and the fiber of two sarcomas, the four fibers contract twice as fast. So a muscle 10 cm long can contract more than twice as fast as a 5 cm muscle. As the load increases, the muscle contraction speed decreases, but the manner in which the speed decreases is the same regardless of the length of the muscles, so it is not worrisome.
● Long muscle has longer the range of contraction than short muscle and faster contraction rate
In other words, for fast joints with large movements, longer muscle than shorter muscle is advantageous. It is a very advantageous structure to earn the length of the muscles that many of the muscles that bend and extend the fingers of the hand are coming out of the distant elbow. If you grasp the fist much from the hyperextension state, the end of the finger of the hand will move more than 270 degrees even against the back of the hand. The fingers can operate instruments and PC keyboards at an unprecedented speed. In addition, thanks to the expulsion of the muscles to the arms, the hands can be made compactly thin and more dexterous.
◆ I have noticed anything strange (so much troubled?) So far. Monkeys and humans that move their fingers and hands frequently communicate with this logic. But dogs and cats also have muscles in their hands out of their elbows. Even cows and horses! Actually all four quadruped animals are almost identical in basic structure. It seems that lizards and frogs also. In the process of evolution going up from the fish to the land, surprisingly, somehow already this basic design was prepared.
○ Referenced sites
· If you want to know more about muscles ⇒Science Channel (18) Body.18 Are muscles stretching and shrinking? (Provided by Japan Science and Technology Agency)
※ Research on muscle contraction was a minimal world from the beginning ⇒JIKEIKAI Medical University Emeritus Professor, Professor Yoshiki Maori’s retirement memorial lecture (2010) (pdf)
· If you want to know more about actin and myosin ⇒Elucidation of motion mechanism of actomyosin, homepage of Osaka University graduate school of life function, Ishima laboratory
・Muscle contraction solid model ⇒“Muscle-Kun Ⅱ”
○ Related articles
◆ 骨格筋収縮の張力 tension of the skeletal muscle contraction
◆ A neural circuit for voluntary movement
◆ アデノシン三リン酸（ATP) adenosine triphosphate
◆ Interaction of myosin and actin
◆ 平滑筋の収縮 smooth muscle contraction
◆ 心筋線維 myocardial fiber
○ Referenced books
SOIL-SHOP Biological teaching material manufacturing plant
rev.20170502, rev.20180321, rev.20180824.