Human Muscular System

The organ system composed of smooth, skeletal, and cardiac muscles is known as the muscular system. This establishes the body balance, helps the body to retain posture, and circulates blood across the body. In vertebrates, the muscular systems are regulated by the nervous system. Some muscles can be fully involuntary (such as the cardiac muscle), whereas some other muscles can be voluntary. It creates the musculoskeletal system along with the skeletal system, which is liable for the complete motion of the human body.

Muscles

Smooth (non-striated) muscles, skeletal muscle, cardiac or heart muscles, are three basic forms of muscles. The muscles tend to provide balance, strength, movement, posture, and heat which helps in keeping the body warm.

Skeletal Muscle

• Like all striated muscles, the skeletal muscles are made up of myocytes, or muscle fibers, that in turn are made up of myofibrils, the essential building block of striated muscle tissue. The myofibrils are made up of sarcomeres. Skeletal muscles tend to show synchronized contraction by shortening each sarcomere when activated by an action potential.

• The sliding filament model of muscle contraction is the best-proposed model for understanding the contraction that occurs between the muscles. Actin and myosin fibers overlap and cross each other in a contractile motion in the sarcomere. Further, Myosin filaments are found to have heads that are club-shaped and project towards the filaments of actin.

• Myosin heads are elongated structures and are observed to attach to myosin filament. These heads are responsible for providing attachment points for the actin filaments at the specific binding sites. In a very synchronized style, the myosin heads move; they tilt towards the middle of the sarcomere, detach, but then reattach to the actin filament's closest active location. This can also be termed as the ratchet type drive system.

• Significant amounts of adenosine triphosphate (ATP) are absorbed during this process. ATP, the cell's energy supply, connects to the cross-bridges between the heads of myosin and the filaments of actin. The production of energy forces the tilting of the head of a myosin. It becomes adenosine diphosphate (ADP) after the use of ATP, and because muscles retain some ATP, they must substitute discharged ADP with ATP on an ongoing basis.

• Muscle tissue often holds a retained reserve of creatine phosphate, a quick-acting recharge chemical, that can facilitate the quick reconstruction of ADP into ATP, if required.

• Each phase of the sarcomere demands calcium ions. When a muscle is induced to contract, calcium is expelled from the sarcoplasmic reticulum to the sarcomere. The actin-binding sites are exposed by this calcium.

• The calcium ions are drained from the sarcomere and down into the sarcoplasmic reticulum for the purpose of storage, whenever the muscle no longer requires to contract.

Cardiac Muscle

• Since the muscle fibers are laterally attached to one another, heart muscles are different from the skeletal muscles. In addition, their action is spontaneous, just as with smooth muscles. The sinus node, regulated by the autonomic nervous system, regulates the muscles of the heart.

Smooth Muscle

• The autonomic nervous system directly regulates smooth muscles and is involuntary, indicating that they are unable to get adjusted by conscious thought. Processes like heartbeat and lungs (that have the ability to regulate voluntarily, be it to a small extent) are involuntary muscles and are not smooth muscles.

Main Functions of the Human Muscular System

• Respiration: The use of the diaphragm muscle is involved in breathing.

A dome-shaped muscle situated under the lungs is the diaphragm. It pushes inward as the diaphragm contracts, allowing the chest cavity to get wider. Then the lungs fill up with oxygen. It forces air out of the lungs as the diaphragm muscle relaxes.

• Posture: When somebody is walking or running, skeletal muscles help hold the body in the right place. This is called posture. Good posture depends on solid muscles that are flexible. Muscles that are rigid, sluggish, or tight lead to poor body posture and misalignment.

• Circulation: A muscle that pumps blood throughout the body is the heart. The heart's movement is beyond conscious control, and when activated by electrical signals, it contracts spontaneously.

• Temperature regulation: A significant feature of the muscular system is the regulation of normal body temperature. Nearly 85 percent of the heat is produced in an individual's body and that is because of the contraction of the muscles. 

• The skeletal muscles enhance their activity to generate heat when body heat falls beneath optimal levels. One instance of this process is shivering. In order to retain body heat, muscles present in the blood vessels also undergo contraction.

Muscle Disorders

• Injury or overuse, including­ sprains or strains, tendonitis, cramps, and bruising

• Genetic problems, such as muscular dystrophy

• Inflammation, such as myositis

• Diseases of nerves that affect muscles, such as multiple sclerosis

• Conditions that cause muscle weakness, such as metabolic, endocrine or toxic disorders; for example, thyroid, and adrenal diseases, alcoholism, pesticide poisoning, medications (steroids, statins), and myasthenia gravis

• Cancers, such as soft tissue sarcoma.

Facts About Muscular System

• The biggest muscle by weight is a muscle called the masseter in the jaw. With a strength of up to 200 pounds on the molars or 55 pounds on the incisors, it helps the teeth to close.

• In the body, the heart is the toughest and hardest muscle. It pumps and produces 5 quarts per minute of blood and 2,000 gallons per day.

• Alongside the smallest bones, the ear includes the tiniest muscles in the body. The internal ear is held together by these muscles and linked to the eardrum.