muscle

• They can Contract, thus becoming thicker
  

• Can stretch when force is applied
  

• Will waste if not enough blood is supplied to them
  

• Will enlarge in response to increased work
  
• Are controlled by nerve stimuli
  
• Are fed from the circulatory system by capillaries that penetrate the fibres.
  

1. Cardiac muscle - Cardiac muscle forms the walls and partitions of the heart, and this muscle tissue contracts rhythmically to squeeze blood into the arteries. This is a special, regular long term job. Imagine having to clench and unclench your fist 72 times a minute, day and night, for the whole of your life. Fortunately, we don't have to remember to contract our cardiac muscle. The action is involuntary, we cannot choose to prevent it from contracting, and neither can we consciously make it contract.
2. Smooth muscle - May also be called visceral or involuntary muscle and is to be found in the walls of the internal (visceral) organs, except for the heart. Examples are the intestines, blood vessels and stomach. This kind of muscle consists of slender, spindle-shaped cells, which are tapered toward both ends. Whereas cardiac and skeletal muscle cells are striated, smooth muscle cells are not striped. Another difference is that smooth cells are much smaller than those found in most skeletal muscles: they are between 0.26 and 0.05 millimetres long. Compared with skeletal muscle, smooth muscle is:
   • more elastic
   • more sensitive to temperature changes and chemical stimuli
   • able to sustain contractions for longer periods
   • slower to contract
3. Skeletal muscle - The skeletal muscles are the ones under conscious control, and they're the only type to play a significant role in voluntary body movement. Skeletal muscle contains several types of fibre. Some fibres are labelled fast-twitch, and others slow-twitch, although other fibres operate between these two extremes. The fast fibres contract more quickly and develop more tension than slow fibres, but sow fibres have greater endurance.

Mus"cle (?), n. [F., fr. L. musculus a muscle, a little mouse, dim. of mus a mouse. See Mouse, and cf. sense 3 (below).]

1. Anat. (a)

An organ which, by its contraction, produces motion

The contractile tissue of which muscles are largely made up.

⇒ Muscles are of two kinds, striated and nonstriated. The striated muscles, which, in most of the higher animals, constitute the principal part of the flesh, exclusive of the fat, are mostly under the control of the will, or voluntary, and are made up of great numbers of elongated fibres bound together into bundles and inclosed in a sheath of connective tissue, the perimysium. Each fiber is inclosed in a delicate membrane (the sarcolemma), is made up of alternate segments of lighter and darker material which give it a transversely striated appearance, and contains, scattered through its substance, protoplasmic nuclei, the so-called muscle corpuscles.

The nonstriated muscles are involuntary. They constitute a large part of the walls of the alimentary canal, blood vessels, uterus, and bladder, and are found also in the iris, skin, etc. They are made up of greatly elongated cells, usually grouped in bundles or sheets.

2.

Muscular strength or development; as, to show one's muscle by lifting a heavy weight.

3. [AS. muscle, L. musculus a muscle, mussel. See above.] Zool.

See Mussel.

Muscle curve Physiol., contraction curve of a muscle; a myogram; the curve inscribed, upon a prepared surface, by means of a myograph when acted upon by a contracting muscle. The character of the curve represents the extent of the contraction.

© Webster 1913.