Smooth Muscle vs Skeletal Muscle
All the movements of animals have been mainly accomplished through the contractions and relaxations of smooth and skeletal muscles. Most of the muscles in the body are not commonly known, but their functions are vital for the survival. The muscles are of three major types known as smooth, skeletal, and cardiac. Out of those three, skeletal muscles are mostly known, cardiac muscles are also known up to a fair extent, but the most common type of smooth are not well known. It would be interesting to explore the characteristics and differences between mostly known and mostly unknown types of muscles. It may be interesting to know whether mostly unknown smooth muscles or the mostly known skeletal muscles play the more important role.
Smooth muscles are non-striated muscles found in the animal bodies and that are functional involuntarily. Smooth muscles are of two major types known as single unit, aka unitary, smooth muscles and multi-unit smooth muscles.
The single unit smooth muscles contract and relax together, as the nerve impulse excites only one muscle cell, and that is passed on to other cells through gap junctions. In other words, a unitary smooth muscle functions as a single unit of cytoplasm with numerous nuclei. On the other hand, the multi-unit smooth muscles have separate nerve supplies to pass signals into separate muscle cells to function independently.
Smooth muscles are found almost everywhere in the body including the alimentary tract, respiratory tract, walls of blood vessels (veins, arteries, arterioles, and aorta), urinary bladder, uterus, urethra, eye, skin, and many other places. Smooth muscles are very flexible and possess a high elasticity. When the tension values are plotted against the length of the smooth muscle, the elasticity properties could be found high. These fusiform-shaped muscles have one nucleus in each cell and the contractions and relaxations being controlled by the autonomic nervous system. That means smooth muscles cannot be controlled as you wish, but those being functional as the way it should be.
Skeletal muscles are one of the striated muscles that are arranged in bundles. The somatic nervous system voluntarily controls the contractions and relaxations of these muscles. Skeletal muscle cells are arranged in bundles of muscle cells, aka myocytes. Myocytes are cylindrically shaped long cells with many nuclei in each. In the cytoplasm, of the myocytes (sarcoplasm) has two major types of proteins known as actin and myosin. Actin in thin and myosin is thick, and these are arranged together in repeating units called sarcomeres. There are zones demarcated in sarcomeres known as A-Band, I-Band, H-Zone, and Z-Disc. Two consecutive Z-Discs make one sarcomere, and the other bands are found inside a sarcomere. The H-Zone is the middle-most zone, and that lies inside the wide and dark coloured A-Band. There are two lightly coloured I-Bands at the two ends of the A-Band. The striated appearance for the skeletal muscle comes from these A-Bands and I-Bands. When the muscle is contracted, the distance between Z-Discs is small, and the I-Band is shortened.
Skeletal muscles are attached to the bones through bundles of collagen fibres called tendons. Ligaments connect muscles with each other. Skeletal muscles are the most common in animal bodies and those can be controlled as you wish.
What is the difference between Smooth Muscle and Skeletal Muscle?
• Skeletal muscles are striated but not the smooth muscles.
• Skeletal muscles are voluntarily controlled while smooth muscles are involuntarily controlled.
• Skeletal muscle cells are multi nucleated, but smooth muscle cells have a single nucleus in each.
• Smooth muscles are found almost everywhere in inner organs, whereas skeletal muscles are found at the outer most section of the body.
• The number of skeletal muscle fibres is highly comparable for the small number of smooth muscle cells.
• Skeletal muscles are long and cylindrical in shape, whereas smooth muscles are fusiform-shaped.