Muscle
From Wikinfo
Muscle is a tissue type found in the bodies of animals . The purpose of muscle is to move a part of the body, often by applying force to the bones. Muscles do this by contracting and relaxing. Contraction is stimulated by electrical impulses transmitted by the nerves, and by the motor nerves and motoneurons in particlular. Muscles and muscular activity account for a lot of the body's energy consumption.
There are three general types of muscle:
- skeletal muscle - a fusion of cells (multinucleated), often voluntary (over 600 in the human body). These enable movement and locomotion.
- smooth muscle - involuntary, such as in the intestines and blood vessels. Surrounds the alimentary canal and most arteries and veins; single, uninucleate fibers.
- cardiac muscle - involuntary but striated, present in the heart.
These three types of cells have many differences, but all use the movement of actin against myosin to produce contraction.
The structure of muscles starts from a basic unit of sacromere which is composed of actin and myosin. Sarcomere are area between Z-lines; shortens during contraction actin myofilaments are thin; myosin are thick (each has "heads" motor neuron stimulus). Sarcomeres line up to make myofibril. Many myobrils are joined together to form a muscle fiber. Muscle fiber are grouped together to form muscle fiber bundles. These bundles are then come together to form muscles.
How skeletal muscle works
- belly of muscle - fibers - myofibrils - myofilaments connective tissue sheaths; sarcolemma
- The strength of skeletal muscle is directly proportional to its cross-sectional area. The strength of a body, however, is determined by biomechanical principles (the distance between muscle insertions and joints, muscle size, and so on).
Fast and Slow skeletal muscle fibers
- red (slow) fibers have many mitochondria; extra stored oxygen in myoglobin; "dark" meat of chickens; endurance
- white (fast) fibers; fewer mitochondria, etc. short, powerful contractions; but fatigue easily (why Arnold Schwartzeneger can't run a marathon); "white" meat of chickens
Motor skills are the abilities of proper use of the muscles. They depend also on the proper functioning of the brain, nerves and joints, and the bones being intact. One application of motor skills is locomotion.
Dexterity is the ability of a person to manipulate objects. It relies on good hand to eye coordination. A criminal application is pickpocketing.
See also : myotomy, sphincter, list of muscles in the human body
References
- Adapted from the Wikipedia article, "Muscle" http://en.wikipedia.org/wiki/Muscle December 27, 2003
