Muscles and Their Functions

Different types of muscles in the body perform different functions according to their type and location. Muscles are the contractile tissues (Tissue that is able to contract) that are responsible for performing various voluntary and involuntary functions. Muscles can be regarded as motors of the body. Muscles are so named because, many of them resemble a mouse, with their tendons representing the tail.


The muscles are of three types, skeletal, smooth and cardiac. However, there is a fourth type, the myoepithelial cells which are specialized cells in sweat glands. The characters of each type are summarized below;

Skeletal Muscles


Skeletal muscles are types of muscles which are most abundant and are found attached to skeleton. They are also called striped, striated, somatic, or voluntary muscles. They exhibit cross-striations under 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 external environment. They also get fatigued very easily.

Each muscle fibre 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.

Skeletal muscles are under highest nervous control of cerebral cortex. Examples of these types of muscles are muscles of limbs and body wall, and bronchial muscles are examples of skeletal muscles.

Most of the skeletal muscles are attached to two bones, one is called origin and other is called insertion. Muscles attach to the bones by tendons which are tough bands of connective tissue. Tendons are very strong and are woven into the coverings of both muscles and bones.

Skeletal muscle may be named on based on their location (tibialis anterior), site of origin and insertion (sternocleidomastoid) , number of Origins (quadriceps), shape (serratus anterior), and function (supinator).

Smooth Muscles or Visceral Muscles


Visceral muscle is found inside of organs like the stomach, intestines, and blood vessels. Visceral muscles are weakest of all the muscles. Their main function is to move substances through the organ. This type of muscles are also called plain, unstriped, non-striated, visceral, or involuntary muscles. These muscles often encircle or surround the viscera.

Visceral muscles are also called involuntary muscles as it is controlled by the part of the brain which cannot be directly controlled by the conscious mind.

Smooth muscles do not exhibit cross-striations under microscope, being plain and smooth in form and their uniform appearance when viewed under a microscope has led to the term smooth muscle which is in contrast with striated appearance of skeletal and cardiac muscles.

They are supplied by autonomic nerves, and, therefore, are not under voluntary control and respond slowly to stimuli. Smooth muscles 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.

Smooth muscles are less dependent on nervous control, being capable of contracting automatically, spontaneously, and often rhythmically and each muscle fibre is an elongated, spindle-shaped cell, with a single nucleus placed centrally; the myofibrils show longitudinal striations. 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 muscles, as the name suggests are 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 and each muscle fiber.

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.

These muscles are found only in the heart and are responsible for pumping blood. Cardiac muscles are also involuntary muscles. Cardiac muscle is unique as it stimulates itself to contract by virtue of pacemaker which is also made of cardiac muscle tissue. Because of this property, cardiac muscle is considered to be autorhythmic or intrinsically controlled.

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 of 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 together by f fingerlike 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 muscle cells to resist high blood pressures and the strain continuous working. These features also help to spread electrochemical signals quickly from cell to cell so that the heart can beat as a unit.

Myoepithelial Cells

These are present at the bases of secretary acini of sweat gland, etc. These help in expulsion of secretion from the acini. Out of the four kinds of muscles, the skeletal muscles are most abundant in the body. These are the only muscles which are dissected out in the dissection hall and studies individually.


Movement and Locomotion

The main function of the muscular system is movement. Skeletal muscles work together with bones and joints to form lever. The muscle acts as the effort force; the joint acts as the fulcrum; the bone acts as the lever; and the object being moved acts as the load. {Second diagram explains the motion}

Posture and Position

Another important function of muscles. The muscles responsible for the body’s posture have the greatest endurance of all muscles in the body as they hold up the body throughout the day without becoming tired.

Movement of Body Substances

The cardiac and visceral muscles are primarily responsible for transporting substances like blood or food from one part of the body to another.

Regulation of Function

They provide motor power for regulating the internal environment related to digestion, circulation, secretion and excretion.

Generation of Body Heat

Due to high metabolic rate of contracting muscle, heat is produced as byproduct. This helps to maintain body temperature. Remember shivering in winters. Muscles are working to produce heat.

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