Cell Morphology and Function: The Specificities of Muscle Cells
Striated skeletal muscles have characteristic cross-striations which are due to the regular arrangement of contractile elements, the sarcomeres. Striated skeletal muscles contract in response to nerve impulses from the motor neurons of the central nervous system (CNS) or at the conscious level. They are related to skeletal segments.
The striated cardiac muscle of the heart is called the myocardium. Microscopically, cardiac muscle fibers are marked by transverse striae, which are also present on skeletal muscle fibers, as well as other transverse striations that make up the joint areas of the fibers. Cardiac muscle contracts independently of the will.
Smooth muscles, as their name implies, do not possess cross-striations. They are generally lighter in color than striated muscles and form the muscular component of the viscera. The walls of organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels, and the erector pili in the skin (which control the erection of body hair) all contain smooth muscle. The contractions of smooth muscles (with very few exceptions) are involuntary and occur under the control of hormones or external stimuli and in response to impulses from the autonomic nervous system.
KeywordsSarcoplasmic Reticulum Thin Filament Skeletal Muscle Fiber Myosin Head Cardiac Muscle Fiber
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