Muscular System


Why do we need it?

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, although some muscles (such as the cardiac muscle) can be completely autonomous.

Three muscle types

1) Smooth muscle - controlled by the autonomic nervous system; may either be generally inactive and then respond to neural stimulation or hormones or may be rhythmic

2) Cardiac muscle - found in the heart, acts like rhythmic smooth muscle, modulated by neural activity and hormones

3) Skeletal muscle - move us around and responsible for most of our behavior; most attached to bones at each end via tendons

Big image

Explain how skeletal muscle contracts, including the release of calcium ions from the sarcoplasmic reticulum, the formation of cross-bridges, the sliding of actin 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 common diseases

  • 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.
  • myasthenia gravis, which is characterized by varying degrees of weakness of the skeletal muscles. Schabbing said. "There are many types of peripheral neuropathies that can be secondary to other medical conditions, such as diabetes, or due to a variety of other causes, including toxins, inflammation and hereditary causes," he said.