Muscle Types

Muscle Types

1. Smooth muscle

   • It is called smooth muscle because its cells do not have stretch marks.
   • It is present in the walls of the organs that contain a lumen such as the urinary bladder, the uterus, the stomach, the intestines and in the walls of the large vascular ducts, such as the arteries and veins of the circulatory system.
   • It is known as involuntary muscle since it is not under voluntary control.
   • Smooth muscle contraction depends on the presence of Ca ions similar to those of skeletal and cardiac muscle.
   • Smooth muscle fibers are much smaller in all dimensions than skeletal and cardiac muscle cells.
   • Smooth muscle fibers have a limited calcium-storing sarcoplasmic reticulum, but have calcium channels in the sarcolemma that open during action potential along the sarcolemma.
   • Most smooth muscles must function for long periods without rest, their power output is relatively low, but contractions can continue without using large amounts of energy.

2. Heart muscle

   • It is a striated muscle that is specifically found in the heart or myocardium.
   • Coordinated muscle contractions pump blood to the vessels of the circulatory system.
   • Its fibers contain a large number of mitochondria.
   • The intercalated discs are part of the sarcolemma and contain two important structures in muscle contraction: gap junctions and desmosomes.
   • The cells of the fibers of the heart muscle are also highly branched and are connected to each other at their ends by interspersed discs.

3. Skeletal muscle

   • One of its most important functions is to contract and cause movement.
   • Small constant contractions of skeletal muscle are needed to maintain an upright body in any position, even at rest.
   • It is found throughout the body at the openings of the internal tracts to control the movement of various substances.
   • These types of muscles protect internal organs by acting as an external barrier or shield against external trauma and by supporting the weight of the organs.
   • Each skeletal muscle is an organ that consists of several integrated tissues, these tissues include skeletal muscle fibers, blood vessels, nerve fibers, and connective tissue.
   • The three levels of connective tissue provide structure to the muscle as a whole and also compartmentalize the muscle fibers within the muscle into groups.
   • Within each skeletal muscle, muscle fibers are organized into individual bundles (called fascicles), by an intermediate layer of connective tissue called the perimysium.