Answer:
Involuntary: Smooth
Voluntary: Skeletal
Electrical Nodes: Cardiac
Tendons: Skeletal
Digestive Tract: Smooth
Arteries: Smooth
Extensors: Skeletal
Step-by-step explanation:
Types of muscles. The three kinds of muscle in the body are the skeletal muscle, the smooth muscle, and the cardiac muscle. The skeletal muscles are attached to the bones and allow one to move at will. Because the skeletal muscles are mostly under your conscious control, they are sometimes called "voluntary" muscles. Smooth muscle lines the inside of such hollow organs as the digestive system, bladder, and arteries. Smooth muscles work automatically and are beyond your conscious control. They are referred to as "involuntary" muscles. Cardiac muscle is unique to the heart.
Although skeletal muscles seem to be under your control, a lot happens of which you are not aware. First of all, your posture, even when asleep, is controlled by skeletal muscles without your paying much attention to it. Your mouth, for instance, would flap open if your brain did not maintain a certain tension in your chewing muscles all the time. Your chin would spend a lot of time resting on your chest if your neck muscles didn't hold your head up. And your movements of all kinds would be pitifully awkward if your cerebellum did not coordinate all the muscles necessary to perform even the simplest actions. Just scratching your nose, for instance, requires dozens of muscles to move in exactly the right way at exactly the right time. You are truly "fearfully and wonderfully made."
We will now take a closer look at the other two types of muscles. Skeletal muscles can be attached to other muscles or to bones either directly or by a thin band of connective tissue called a tendon. Do not confuse this tendon with a ligament, which connects bone to bone and not muscle to bone. Two good examples of tendons can be found in the back of your legs. One is the Achilles tendon which attaches the calf muscle in the lower back part of your leg to your heel. The other tendons are on the back side of your knee, called the hamstrings. They serve to attach muscles in the upper back part of the leg to the bones of the lower leg and flex your knee. Locate these structures on your own leg.
The point at which a muscle is attached to the less movable part of the body is called the origin. The point at which a muscle is attached to the more movable part of the body is called the insertion. The biceps muscle of your upper arm is a good example of both these points. The biceps has its origin in your shoulder and its insertion in the bones of the forearm.
Skeletal muscles differ relative to their effect on the body. Those muscles that bend a joint are called flexors, and those muscles that straighten a joint are called extensors. Muscles always work in pairs, one opposing the action of the other. For instance, the upper arm has biceps on the front, which serves as the flexor. The muscle that opposes this motion and serves as the extensor of the forearm is the triceps, which is located on the back of the upper arm. When one muscle contracts, the other must relax. Study the diagram and then see if you can feel the alternating contraction of the biceps and triceps in your own upper arm as you bend and straighten it.
You should be careful to get enough exercise to keep your muscles in good shape. Muscles will grow larger and have better tone, which means they will always be slightly contracted, if they are used. If a person is lazy or is confined to a bed or wheelchair for a prolonged period of time, the muscles not being used will become smaller and lose their tone. This condition is called atrophy. A muscle atrophies at a rate of about 1% a day, so that it will lose a full third of its strength after a month of disuse. Disuse also causes bones to soften by losing their calcium. "Use it or lose it" is a solid maxim of physiology.