Muscular system

Why its important

The function

The muscular system is responsible for the movement of the human body. Attached to the bones of the skeletal system are about 700 named muscles that make up roughly half of a person’s body weight. Each of these muscles is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves. Muscle tissue is also found inside of the heart, digestive organs, and blood vessels. In these organs, muscles serve to move substances throughout the body.

Three types of muscle tissue

The 3 types of muscle tissue are cardiac, smooth, and skeletal. Cardiac muscle cells are located in the walls of the heart, appear striated, and are under involuntary control. Smooth muscle fibers are located in walls of hollow visceral organs, except the heart, appear spindle-shaped, and are also under involuntary control. Skeletal muscle fibers occur in muscles which are attached to the skeleton. They are striated in appearance and are under voluntary control.

show the structure of a sarcomere, including Z lines,actin filaments, myosin filaments with heads, and the light and dark bands.

  • The H zone is the area only occupied by the thick filaments (myosin)
  • The I bands (light) are the regions occupied by only thin filaments (actin)
  • The A bands (dark) are the regions occupied by both filaments (overlap)
  • The Z lines represent the extremities of a single sarcomere

Explaining how skeletal muscle contracts, including the release of calcium ions from the sarcoplasmic reticulum, the formation of cross-bridges, the sliding of act in and myosin filaments and the use of ATP.

  • An action potential from a motor neuron triggers the release of Ca2+ ions from the sarcoplasmic reticulum
  • Calcium ions expose the myosin heads by binding to a blocking molecule (troponin complexed with tropomyosin) and causing it to move
  • The myosin heads form a cross-bridge with actin binding sites
  • ATP binds to the myosin heads and breaks the cross-bridge
  • The hydrolysis of ATP causes the myosin heads to change shape and swivel - this moves them towards the next actin binding site
  • The movement of the myosin heads cause the actin filaments to slide over the myosin filaments, shortening the length of the sarcomere
  • Via the repeated hydrolysis of ATP, the skeletal muscle will contract

2 Major disorders that occur in this system

Common primary muscle disorders include inflammatory myopathies, including polymyositis, which is characterized by inflammation and progressive weakening of the skeletal muscles; dermatomyositis, which is polymyositis accompanied by a skin rash; and inclusion body myositis, which is characterized by progressive muscle weakness and wasting.

Other common disorders are muscular dystrophies and metabolic muscle disorders. Muscular dystrophy affects muscle fibers. Metabolic muscle disorders interfere with chemical reactions involved in drawing energy from food.Neuromuscular junction disorders impair the transmission of nerve signals to muscles.