Different Types and Functions of Muscles

Types of Muscles 
Humans have three types of muscle tissue: smooth, cardiac, and skeletal. The contractile cells of these tissues are called muscle fibers.
Smooth muscle fibers are spindle-shaped cells, each with a single nucleus (uninucleated). The cells are usually arranged in parallel lines, forming sheets. The striations (bands of light and dark) seen in cardiac and skeletal mus­cle are not found in this tissue. Smooth muscle is located in the walls of hollow internal organs. Contraction of smooth muscle is involuntary, occurring without conscious con­trol. Although smooth muscle is slower to contract than skeletal muscle, it can sustain prolonged contractions and does not fatigue easily.
Cardiac muscle fibers are uninucleated, striated, cylindricaL and branched, which allows the fibers to in­terlock at intercalated disks. Intercalated disks permit con­tractions to spread quickly throughout the heart. Cardiac fibers relax completely between contractions, which pre­vents fatigue. Contraction of cardiac muscle is rhythmical; it occurs without outside nervous stimulation and with­out conscious control. Thus, cardiac muscle contraction is involuntary.
Skeletal muscle fibers are cylindricaL multinucleated, and striated. They make up the skeletal muscles attached to the skeleton. They run the length of the muscle and can be quite long. Skeletal muscle is voluntary because its contraction can be consciously stimulated and controlled by the nervous system.
Uninucleated, spindle-shaped fibers make up the involuntary smooth muscle found in the \Nalls of hollo\N internal organs. Uninucleated. branched. and striated fibers vvith intercalated disks make up the involuntary cardiac muscle of the heart. Multinucleated, striated, and cylindrical fibers make up the voluntary skeletal muscle attached to the skeleton.
Functions of Muscles
Muscles have at least four functions:
The tendons of skeletal muscles often extend across joints, thereby stabilizing the joints. The skeleton would fall apart if joints were not stabilized by tendons and ligaments.
Muscle contraction opposes the force of gravity and allows us to remain upright. Muscle contraction re­finements allow us to assume different positions.
Muscle contraction produces movements. Skeletal muscle contraction accounts for body movements, eye movements, and facial expressions, and also contributes to breathing. Smooth muscle contraction moves food in the digestive tract and reduces the size of blood vessels. Cardiac muscle contraction pumps the blood.
Muscle contraction produces heat, which is used to maintain body temperature.
Muscle tendons extend across joints. stabilizing them. Muscle contraction allows us to remain upright, produces movement of the body and internal organs, and creates heat that vvarms the body.