The Muscular System
    
The muscular system is an organ system consisting of skeletal, smooth and cardiac muscles. It permits movement of the body, maintains posture, and circulates blood throughout the body. The muscular system in vertebrates is controlled through the nervous system...
Muscles

There are three distinct types of muscles: skeletal muscles, cardiac or heart muscles, and smooth (non-striated) muscles. Muscles provide strength, balance,posture, movement and heat for the body to keep warm.

Upon stimulation by an action potential, skeletal muscles perform a coordinated contraction by shortening each sarcomere. The best proposed model for understanding contraction is the sliding filament model of muscle contraction.Actin and myosin fibers overlap in a contractile motion towards each other. Myosin Filaments have club-shaped heads that project toward the actin filaments.

Larger structures along the myosin filament called myosin heads are used to provide attachment points on binding sites for the actin filaments. The myosin heads move in a coordinated style, they swivel toward the center of the sarcomere, detach and then reattach to the nearest active site of the act infilament. This is called a rachet type drive system. This process consumes large amounts of adenosine triphosphate (ATP).

Energy for this comes from ATP, the energy source of the cell. ATP binds to the cross bridges between myosin heads and actin filaments. The release of energy powers the swiveling of the myosin head. Muscles store little ATP and so must continuously recycle the discharged adenosine diphosphate molecule (ADP) into ATP rapidly. Muscle tissue also contains a stored supply of a fast acting recharge chemical, creatine phosphate which can assist initially producing the rapid regeneration of ADP into ATP.

Calcium ions are required for each cycle of the sarcomere. Calcium is released from the sarcoplasmic reticulum into the sarcomere when a muscle is stimulated to contract. This calcium uncovers the actin binding sites. When the muscle no longer needs to contract, the calcium ions are pumped from the sarcomere and back into storage in the sarcoplasmic reticulum.

Aerobic & Anaerobic
Muscle Activity

At rest, the body produces the majority of its ATP aerobically in the mitochondria without producing lactic acid or other fatiguing byproducts. During exercise, the method of ATP production varies depending on the fitness of the individual as well as the duration, and intensity of exercise. At lower activity levels, when exercise continues for a long duration (several minutes or longer), energy is produced aerobically by combining oxygen with carbohydrates and fats stored in the body. Activity that is higher in intensity, with possible duration decreasing as intensity increases, ATP production can switch to anaerobic pathways, such as the use of the creatine phosphate and the phosphagen system or anaerobic glycolysis...
1. Dermatomyositis
The main symptoms include skin rash and symmetric proximal muscle weakness which may be accompanied by pain. The pain may resemble the type experienced after strenuous exercise. Some dermatomyositis patients have little pain, while in others (esp. in JDM), the pain may be severe. It is important to remember that this condition varies from person to person in many ways. Also in many cases muscle may deteriorate and render the patient temporarily paralyzed unable to walk, run, get out of bed, or even swallow food and liquids.
2. Myositis
Myositis can occur in a variety of diseases and is generally a sign of collagen diseases, that is, systemic diseases of connective tissue. The disease may be acute, subacute, or chronic. Muscle symptoms are often combined with skin disturbances (reddening, edema, induration)—dermatomyositis. Patients complain of pain in the muscles, muscular weakness, and incoordination; muscular sclerosis and contractures develop in the later stages of the disease.

3. Polymyositis
Symptoms include pain, with marked weakness and/or loss of muscle mass in the proximal musculature, particularly in the shoulder and pelvic girdle. The hip extensors are often severely affected, leading to particular difficulty in ascending stairs and rising from a seated position. The early symptoms of PM and DM are slowly progressing muscle weakness, usually symmetrical between the two sides of the body. PM and DM affect primarily the muscles of the trunk and those closest to the trunk, while the hands, feet, and face usually are not involved. Weakness may cause difficulty walking, standing, and lifting objects. Rarely, the muscles of breathing may be affected. Weakness of the muscles used for swallowing can cause difficulty with swallowing (dysphagia). Joint pain and/or swelling also may be present. Later in the course of these diseases, muscle wasting or shortening (contracture) may develop in the arms or legs.
4. Inclusion Body Myositis
Eventually, IBM results in general, progressive muscle weakness. The muscles in the thighs called the quadriceps and the muscles in the arms that control finger flexion—making a fist—are usually affected early on. Common early symptoms include frequent tripping and falling, weakness going up stairs and trouble manipulating the fingers—turning doorknobs, gripping keys, etc. Foot drop in one or both feet has been a symptom of IBM and advanced stages of polymyositis (PM).

During the course of the illness, the patient's mobility is progressively restricted as it becomes hard for him or her to bend down, reach for things, walk quickly and so on. Many patients say they have balance problems and fall easily, as the muscles cannot compensate for an off-balanced posture. Because IBM makes the leg muscles weak and unstable, patients are very vulnerable to serious injury from tripping or falling down. Although pain has not been traditionally part of the "textbook" description, many patients report severe muscle pain, especially in the thighs.
5. Fibromyalgia
The term "fibromyalgia" derives from new Latin, fibro-, meaning "fibrous tissues", Greek myo-, "muscle", and Greek algos-, "pain"; thus the term literally means "muscle and connective tissue pain". The defining symptoms of fibromyalgia are chronic widespread pain, fatigue, and heightened pain in response to tactile pressure (allodynia). Other symptoms may include tingling of the skin, prolonged muscle spasms, weakness in the limbs, nerve pain, muscle twitching, and palpitations. 
6. Lupus
The most commonly sought medical attention is for joint pain, with the small joints of the hand and wrist usually affected, although all joints are at risk. The Lupus Foundation of America estimates more than 90 percent of those affected will experience joint and/or muscle pain at some time during the course of their illness.
7. (MCTD)
MCTD combines features of scleroderma, myositis, systemic lupus erythematosus, and rheumatoid arthritis (with some sources adding polymyositis, dermatomyositis, and inclusion body myositis) and is thus considered an overlap syndrome.
8. Stiff Person's Disease
SPS will begin insidiously in the axial muscles. Patients will present with an exaggerated upright posture and have stiffness and pain in the whole back. Sleep disturbances are also common due to muscle spasms waking them. In the late stages, proximal limb muscle become involved and the patient tends to move slower as fast movements will cause the severe spasms. Emotions such as anger have been shown to have a link to causing the spasms, which begin in this stage.

Symptoms begin in the region of the trunk and the lower extremities before moving proximally in the upper limbs, and eventually affecting facial and laryngeal muscles used for swallowing and speech.

In the variant Stiff-limb syndrome, symptoms present focally affecting one or more limbs. Motor symptoms occur predominantly in distal limb muscles rather than axial muscles. However, when patients experience severe spasms, motor symptoms can be seen in the trunk, upper extremities and face. Increased distal limb stiffness in ankles and feet leads to feet being in constant plantar flexion. This in turn affects posture during gait and increase fall risks for the patient.
9. Polymyalgia Rheumatica
Takes its name from the word "polymyalgia" which means "pain in many muscles" in Greek followed by the term "rheumatica") abbreviated as PMR, is a syndrome with pain or stiffness, usually in the neck, shoulders, and hips. The pain can be very sudden, or can occur gradually over a period. Most PMR sufferers wake up in the morning with pain in their muscles; however, there have been cases in which the patient has developed the pain during the evenings. There are a wide range of symptoms that indicate if a person has polymyalgia rheumatica. The classic symptoms include:
  • Pain and stiffness (moderate to severe) in the neck, shoulders, and hips, which inhibits activity, especially in the morning/after sleeping.
  • Fatigue and lack of appetite (possibly leading to weight loss) are also indicative of polymyalgia rheumatica.
The modification date for all health, and medical content on this page was last updated, and checked on May 20th, 2018 PST U.S.A.