Smooth Muscles, Cardiac Muscle, and Cardiac muscle.
Explanation:
Smooth Muscles
Visceral muscle is found inside organs like the stomach, intestines, and blood vessels. Visceral muscles are the weakest of all the muscles. Their main function is to move substances through the organ. This type of muscle is also called plain, unstriped, non-striated, visceral, or involuntary muscles. Visceral muscles are also called involuntary muscles as they are controlled by the part of the brain which cannot be directly controlled by the conscious mind. Smooth muscles do not exhibit cross-striations under a microscope, being plain and smooth in form and their uniform appearance, when viewed under a microscope, has led to the term smooth muscle. The smooth muscle fiber is an elongated, spindle-shaped cell, with a single nucleus placed centrally; the myofibrils show longitudinal striations. They are supplied by autonomic nerves and are capable of sustained contraction, and, therefore, do not fatigue easily. They provide motor power for regulating the internal environment related to digestion, circulation, secretion, and excretion. These are less dependent on nervous control, being capable of contracting automatically, spontaneously, and often rhythmically. Muscles of the blood vessels, and the arrector pili or erector pili muscles of the skin are examples of smooth muscles.
Cardiac Muscle
This type of muscle, as the name suggests is found in the heart. It is intermediate in structure, being striated and at the same time involuntary. It is meant for automatic and rhythmic-contractions. These fibers have a single nucleus placed centrally which branches and anastomoses with the neighboring fibers at intercalated discs (apposed cell membranes). The cross-striations are less prominent than those in the skeletal muscle. It is responsible for pumping blood. It is unique as it stimulates itself to contract [autorhythmic or intrinsically controlled] by a pacemaker which is also made of cardiac muscle tissue. The cells of cardiac muscle tissue are striated—that is, they appear to have light and dark stripes when viewed under a light microscope. The arrangement of protein fibers inside the cells causes these light and dark bands. Striations indicate that a muscle cell is very strong, unlike visceral muscles. The cells of cardiac muscle are branched X or Y-shaped cells tightly connected by finger-like projections from two neighboring cells [called intercalated discs] that interlock and provide a strong bond between the cells. The branched structure and intercalated discs allow the cells to resist high blood pressures and the strain of continuous working. These features also help to spread electrochemical signals quickly from cell to cell so that the heart can beat as a unit.
Skeletal Muscles
Skeletal muscles are types of muscles that are most abundant and are found attached to the skeleton. They are also called striped, striated, somatic, or voluntary muscles. They exhibit cross-striations under the microscope and are considered to be the best-differentiated form of muscle. They are supplied by somatic (cerebrospinal) nerves, and, therefore, are under voluntary control, with certain exceptions. They respond quickly to stimuli, being capable of rapid contractions, and help in adjusting the individual to an external environment. They also get fatigued very easily. Each muscle fiber of skeletal muscle is a multinucleated cylindrical cell, containing groups of myofibrils. Myofibrils are made up of myofilaments of three types (myosin, actin, and tropomyosin). These are the actual contractile elements of the muscle. These are under the highest nervous control of the cerebral cortex. Examples of these types of muscles are muscles of limbs and body wall, and bronchial muscles are examples of skeletal muscles.
