Skip to main content

Developmental Biology Boot Camp

Muscle Tissue

Electron micrographs of different class of muscle at the same magnification. Image provided by the University of Michigan Medical School (OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)])
Electron micrographs of different class of muscle at the same magnification. Image provided by the University of Michigan Medical School (OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)])
 What are some general features of muscle?

Muscle is a relatively large tissue with an enormous range of structural and functional characteristics in humans. Muscle tissue can be one of three forms: skeletal, cardiac, or smooth. Skeletal muscle and cardiac muscle are both called striated due to the presence of striped patterns of repeating or bundled cells. This type of muscle contains sarcomeres and contracts in relatively transient bursts, in contrast with smooth muscle, which sustains prolonged or even near-permanent contractions. Our discussion focuses on skeletal muscle.

 

Inside a cardiomyocyte. (Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)])
Inside a cardiomyocyte. (Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)])
 What makes skeletal muscle cells unique? 

Relative to cells of other tissues, skeletal muscle cells are among the largest in the body. These cells contain more than one nucleus. It is unclear precisely why this is the case but is most likely related to allowing a single, elongated muscle fiber to have better spatial control over transcription of mRNAs across the cell body or maintain protein quantities that are sufficient for the relatively large cell volume. Unique to other somatic cells, the plasma membrane of muscle cells is called the sarcolemma, and the cytoplasm the sarcoplasm. Abundant within the sarcoplasm are glycogen-containing granules as well as myoglobin and calcium, the primary regulator of muscle contraction. Unlike traditional plasma membranes, the sarcolemma invaginates into the cytoplasm at specialized structures known as transverse- (T-) tubules. These are abundant along the cell body, permitting rapid diffusion of ions, and thus permeation of an action potential, across the muscle cell.