Muscles, as a whole, make up the organ system of musculature that allows the human body to move. Muscles are cells that have the ability to contract in response to a specific stimulus using energy as sugar and oxygen from the blood.
What are muscles?
Muscles are broadly divided into the skeletal muscles of the musculoskeletal system, the smooth muscles of the internal organs, and the cardiac muscle. While skeletal muscles can be controlled at will, smooth muscles work largely independently of a person’s intentions. In the digestive system, for example, smooth muscle cells perform their work at their own speed and cannot be influenced by a person’s will. In a similar way, it is hardly possible to make the heart beat at will because the heart muscle tissue is also not subject to a person’s will.
Anatomy and structure
Muscles of the musculoskeletal system are usually composed of a muscle belly and two tendons, which are usually attached to bones or connective tissue planes. Some muscles are also composed of two or more muscle bellies with a corresponding number of tendons. The muscle belly is surrounded by a connective tissue sheath and is divided into numerous bundles of muscle fibers. The core of each muscle fiber is a contracting protein meshwork of mainly three proteins, myosin, actin and troponin. The actin forms a system of short fibers that resemble the spars in a ladder. Between each two actin spars, myosin proteins are attached with the help of springy troponin proteins. In response to the appropriate nerve signal, the myosin proteins climb up the actin spars like a real ladder, allowing the muscle to shorten. Cardiac muscle cells are distinguished from other types of muscle by the fact that they can also feed directly, in part, on fats and cholesterol from the bloodstream and generate electrical impulses from themselves at a certain heart rate and also pass them on to all other cells cell by cell so that the heart can beat as a whole and in a coordinated manner.
Functions and tasks
Due to the structure of the muscles, a muscle can only shorten or relax. To allow movement of the limbs and the body and trunk in all directions, the muscles of the musculoskeletal system are each arranged in counterparts. Thus, the two-bellied arm muscle is responsible for flexion in the elbow joint, while the arm muscle with the three muscle bellies performs extension in the elbow joint as its counterpart. Another peculiarity in the functioning of muscles is that a muscle rarely performs only one task. Usually, several joints are moved in different directions by the same muscle. For example, the two-headed arm muscle not only flexes the arm at the elbow joint, it also lifts the arm away from the body with its longer muscle belly or guides it back toward the body with its shorter muscle belly. It also assists in the forward swing of the arm as well as the inward rotation of the entire arm. Additionally, it is the strongest muscle turning the forearm inward. On the other hand, within the body, the smooth muscles have the function of contracting in the internal organs including the blood vessels. One of the characteristics of smooth muscle cells is that they can not only contract and relax, but also remain in a contracted state.
Diseases
The most common ailments that can occur in skeletal muscles are muscle stiffness, muscle strain along with muscle soreness or muscle cramps. Diseases that can occur in the muscles include a variety of genetic muscle weakness diseases such as Becker syndrome, in which the body cannot properly produce an essential protein in the muscle, causing the muscle to become nonfunctional and weak. Many metabolic diseases or nerve diseases such as paralysis show up in the muscles. There are also anti-immune diseases caused by the body’s own defense system. On the other hand, the other two types of muscles are affected by other diseases. If there is insufficient oxygen supply, it can range from heart pain to heart attack.
Typical and common diseases
- Muscle fiber tear
- Muscle weakness
- Compartment syndrome
- Muscle inflammation (myositis)
- Muscular atrophy (muscular dystrophy)
