Muscular Tissue

Muscular tissue is a specialized tissue in animals which applies forces to different parts of the body by contraction. It is made up of thin and elongated cells called muscle fibers. It controls the movement of an organism.

The cytoplasm in the muscle fibers is called sarcoplasm. It contains a network of membrane called the sarcoplasmic reticulum. The membrane surrounding the muscle fibers is called sarcolemma.

Properties of Muscular Tissue

  1. Contractibility– It is the ability of muscle cells to shorten forcefully.

  2. Extensibility– A muscle has the ability to be stretched.

  3. Elasticity– The muscles have the ability to recoil back to its original length after being stretched.

  4. 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 force on the organs and control everything from circulation to food processing.

Also Read: Sliding Filament Theory

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 contractibility and extensibility of the muscles.

  • Skeletal muscles are voluntary muscles composed of muscle fibers.

  • 40% of our body mass comprises of 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.

Muscular Tissue Function

The muscular tissues are connected to the same nerve bundles.

The nerve impulse from the brain tells the muscles to contract.

Each muscle cell contains the proteins actin and myosin. These proteins slide past one another when the signal is received for contraction.

A single cell contracts up to 70% in length. The entire muscle shortens during contraction.

Muscular tissues help in the movement of bones, squeeze different organs, or compress chambers.

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Important Questions

Q.1 What is the main function of muscular tissue?

A.1. Movement is the main function of muscular tissue. They have the ability to contract and this is what brings about the movement of body parts. They also help to maintain body posture and position.

Q.2. What are the distinguishing features of the three types of muscular tissues?

A.2. The skeletal muscles are attached to the bones and help in its movement, the smooth muscles perform the involuntary functions, and the cardiac muscles are found in the heart and help in the pumping of blood through cardiac contractions.

Q.3. What are the different types of muscle fibers?

A.3. There are three types of muscle fibers:

  • Red/Fast (slow twitch or type I fibers)
  • Red/Slow (fast oxidative or type IIa fibers)
  • White/Fast (fast glycolytic or type IIb fibers)

Q.4. How are slow twitch muscle fibers different from fast twitch muscle fibers?

A.4. Slow twitch muscle fibers enable long endurance such as distance running, whereas, the fast twitch muscle fibers fatigue faster and are used in powerful bursts of movement.

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