New Chapt 15-Skeletal muscle(1)

New Chapt 15-Skeletal muscle(1) - CHAPTER 15 SKELETAL...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
161 CHAPTER 15 SKELETAL MUSCLE Muscles in the body are generally divided into two broad categories: striated muscles and smooth muscles. The striated muscles include both cardiac muscle (the muscle of the heart) and the skeletal muscles (the muscles which are attached to the bones of the body and are responsible for the movement of parts of the skeleton). Skeletal muscle is said to be under voluntary nervous system control because the activity of this muscle type can be consciously controlled. Smooth muscle lines hollow structures in the body such as the stomach, intestinal tract, bladder, blood vessels, uterus. The contraction of smooth muscles (as well as of cardiac muscle) is under control of the autonomic nervous system (i.e., the sympathetic and parasympathetic nervous systems) and normally can not be consciously controlled. The distinctions between cardiac and skeletal muscle are largely functional and morphological. Furthermore, the basic mechanism by which all three muscle types contract are very similar. Skeletal muscle Skeletal muscle is a good place to start our consideration of muscle. It has been the most thoroughly studied muscle type, and, in any case, we will see that the contractile mechanisms of skeletal muscle also apply to smooth and cardiac muscle. The basic cellular element in a skeletal muscle is the muscle fiber . Muscle fibers are cylindrical and vary in size from 5-100 μ (microns) in diameter and can be many inches in length. Although one muscle fiber is one single cytoplasmic mass, it is actually the result of the fusion of many hundreds of cells called myoblasts during embryonic and early post-embryonic development. Thus, a muscle fiber is a multinucleate cell--the nuclei of a muscle fiber are scattered along its entire length. The term muscle refers to a number of muscle fibers bound together by connective tissue. (A muscle fiber is to a muscle much as an axon is to a nerve.) The muscle fibers in an individual muscle (the number may vary from a few hundred to several thousand) are linked by connective tissue at each end form bundles of collagen fibers known as tendons . Tendons act as the structural framework by which muscles are attached to the bones they act to move; tendons do not themselves have any contractile properties. Structure of a skeletal muscle fiber The most striking feature of skeletal muscle fibers seen through the light microscope is a series of repeating transverse light and dark bands forming a regular pattern along each muscle fiber. These bands or striations are characteristic of both skeletal muscle fibers and cardiac muscle fibers (hence the name striated muscle). Upon closer examination it is found that each muscle fiber itself has collected within its cytoplasm numerous (several hundred to several thousand, depending on the diameter of the muscle fiber) smaller cylindrical elements known as myofibrils (1-2 μ in diameter), which are, arrayed parallel to each other and extend the length of the muscle fiber. The striations transversing the muscle fiber actually result from the bands present in the myofibrils themselves.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/19/2011 for the course BIO 365R taught by Professor Draper during the Spring '08 term at University of Texas at Austin.

Page1 / 19

New Chapt 15-Skeletal muscle(1) - CHAPTER 15 SKELETAL...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online