I. Definition:
Muscle is a specialized tissue that has two abilities:
- Contract
- Conduct electrical impulses.
II. Type:
- Muscle tissue can be divided due to their structures and the function
- There are 3 types of muscle tissue:
(i) Smooth involuntary muscle ( Smooth muscle)
- Single, large, oval nucleus.
- Filled with a specialised cytoplasm, the sarcoplasm and surrounded by a membrane- sarcolemma.
- Smooth muscle is involuntary tissue ( not controlled by the brain)
- Position:
+) walls of hollow organs.
+) walls of the bladder, uterus
+) walls of blood vessels.
- Function:
+) Control the contraction of the smooth muscle tissue in the walls of the intestine and stomach.
+) Regulate the blood pressure and the flow of blood (through controlling the contraction and relaxation of the muscle of the arteries).

(ii) Striated voluntary muscle ( Skeletal muscle)
- Bind into bones by tendons.
- Have striations and many nuclei (multinucleated)
- The nuclei are found at the periphery of the cell
- Smaller unit of muscle fiber : myofibril, consist of actin and myosin filaments
+) Actin: Light bands ( I- bands) - Attached to Z-line.
+) Myosin: Dark bands ( A-band) – Thicker than Actin.
- The arrangement of actin and myosin filaments is known as a sacromere.
- In almost part of the body
- Function:
+) Co-ordinated movements of the limbs, trunk, jaws, eyeballs, etc.
+) Taking part in breathing process.

(iii) Striated involuntary muscle (Cardiac muscle)
- Have cross-striations and contain numerous nuclei
- It is involuntary
- Only one nucleus
- Position: only in the walls of the heart.
- Function:
+) Contraction of the atria and ventricles of the heart
+) Causes the rhythmical beating of the heart.