The muscle cells are also known as muscle fibres because they are thin, long and cylindrical. They are arranged parallel to each other. The muscle fibres are composed of numerous fine fibrils called myofibrils.
The muscular tissue is responsible for locomotion and various types of movements in the body organs. The contraction and relaxation of muscle tissue bring about the movement. When the cells receive a stimulus, the cells will contract (shorten) and then returns to the original state (relaxation). This cycle repeats continuously to facilitate muscle movement.
There are 3 types of muscle tissues.
Skeletal or Striated Muscle
- The muscles which are found in close association with skeletal bones are called skeletal muscles.
- They are also called voluntary muscle because the action of skeletal muscles is completely under voluntary control.
- Striated muscles are composed of long, thin and multinucleated fibres. These fibres are crossed with fine red and white lines, which gives the muscles a distinctive striated appearance, and hence the name.
- A sheath of connective tissue bounds several bundles of muscle fibres together.
Smooth Muscle
- Smooth muscles are unstriated and involuntary muscles. The term ‘smooth’ refers to the absence of the striations.
- The muscle fibres are spindle-shaped cells with tapering ends (fusiform) and a centrally located nucleus. They are bundled together in a connective tissue sheath.
- Smooth muscle is generally seen on the wall of blood vessels and hollow internal organs such as stomach and intestines.
Cardiac Muscle
- Cardiac muscle is also called myocardium.
- It is a contractile tissue present only in the heart.
- Cardiac muscle is similar to skeletal muscles in having striations, and contractile units (sarcomeres).
- However, it differs from skeletal muscles in that it is involuntary and shows rhythmic contractions.
- These rhythmic contractions are regulated by the SA node (sinoatrial node) of the heart. It acts as the heart’s pacemaker.
- The plasma membranes of the cardiac cells fuse together through cell junctions and make them stick together.
- Communication junctions (or intercalated discs) allow the cells to contract as a single unit.
| Skeletal Muscles | Smooth muscles | Cardiac muscles |
| Striations – present | Striations – absent | Striations – present |
| Voluntary muscles | Involuntary muscles | Involuntary muscles |
| Multinucleate cells | Uninucleate cells | Uninucleate cells |
| Fibres – Cylindrical and unbranched | Fibres – Spindle-shaped | Fibres – Cylindrical and branched, with intercalated discs |
