Muscle tissue is composed of cells that have the special ability to shorten or contract in order to produce movement of the body parts. The tissue is highly cellular and is well supplied with blood vessels.
Functions of muscle tissue
- Movement:Our body’s skeleton gives enough rigidity to our body that skeletal muscles can yank and pull on it, resulting in body movements such as walking, chewing, running, lifting, manipulating objects with our hands, and picking our noses.
- Maintenance of posture: Without much conscious control, our muscles generate a constant contractile force that allows us to maintain an erect or seated position, or posture.
- Respiration: Our muscular system automatically drives movement of air into and out of our body.
- Heat generation: Contraction of muscle tissue generates heat, which is essential for maintenance of temperature homeostasis. For instance, if our core body temperature falls, we shiver to generate more heat.
- Communication: Muscle tissue allows us to talk, gesture, write, and convey our emotional state by doing such things as smiling or frowning.
- Constriction of organs and blood vessels: Nutrients move through our digestive tract, urine is passed out of the body, and secretions are propelled out of glands by contraction of smooth muscle. Constriction or relaxation of blood vessels regulates blood pressure and blood distribution throughout the body.
- Pumping blood: Blood moves through the blood vessels because our heart tirelessly receives blood and delivers it to all body tissues and organs.
- This isn’t a complete list. Among the many possible examples are the facts that muscles help protect fragile internal organs by enclosing them, and are also critical in maintaining the integrity of body cavities. For example, fetuses with incompletely formed diaphragms have abdominal contents herniate (protrude) up into the thoracic cavity, which inhibits normal lung growth and development. Even though this is an incomplete list, an appreciation of some of these basic muscle functions will help you as we proceed.
Types of Muscular Tissue
The muscular tissue is of three types:
- Skeletal Muscle Tissue
- Smooth Muscle Tissue
- Cardiac Muscle Tissue
Skeletal Muscle Tissue
- These muscles are attached to the skeleton and help in its movement.
- These muscles are also known as striated muscles because of the presence of alternate patterns of light and dark bands.
- These light and dark bands are sarcomeres which are highly organized structures of actin, myosin, and proteins. These add to the contractility and extensibility of the muscles.
- Skeletal muscles are voluntary muscles composed of muscle fibers.
- 40% of our body mass comprises skeletal muscles.
- Each skeletal tissue contains myofibrils.
- The cells of these tissues are multinucleated.
- These are provided with blood vessels and many elongated mitochondria and glycogen granules.
- They bring about the movement of the organs of the body.
Smooth Muscle Tissue
- These are non-striated, involuntary muscles controlled by the Autonomous Nervous System.
- It stimulates the contractility of the digestive, urinary, reproductive systems, blood vessels, and airways.
- The actin and myosin filaments are very thin and arranged randomly, hence no striations.
- The cells are spindle-shaped with a single nucleus.
Cardiac Muscle Tissue
- These are found only in the heart.
- These are involuntary muscles and the heart pumps the blood through cardiac contractions.
- The cells of the cardiac muscles known as the cardiomyocytes are striated.
- They are single-celled and uninucleated.
- The ends of the cells are joined and the junctions are called intercalated discs. The cells are attached to each other by desmosomes.
Properties of Muscular Tissue
- Contractibility– It is the ability of muscle cells to shorten forcefully.
- Extensibility– A muscle has the ability to be stretched.
- Elasticity– The muscles have the ability to recoil back to its original length after being stretched.
- Excitability– The muscle tissue responds to a stimulus delivered from a motor neuron or hormone.
Structure of Muscular Tissue
The muscular tissues are bundled together and surrounded by a tough connective tissue similar to cartilage known as epimysium.
The bundle of nerve cells that run in long fibers called fascicles are surrounded by the epimysium.
The fascicles are surrounded by a protective layer known as perimysium. It allows the flow of nerves and blood to the individual fibers.
Another protective layer, the endomysium surrounds the fibers.
These layers and muscles help in the contraction of different parts of the muscles. The different bundles slide past one another as they contract.
The epimysium connects to the tendons attached to the periosteum connective tissue that surrounds the bones. This helps in the movement of the skeleton when the muscles contract.
The epimysium connects to other connective tissues to produce a force on the organs and control everything from circulation to food processing.
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