• Muscular cells are mesodermal in origin. Iris muscles in the eye are ectodermal)
• Muuscle cells are irritable.
• They are specialized for contraction. Muscle contraction brings about movement.
• Muscle tissue in mammals can be distunguished into three types on the basis of location, and structural and functional characterstics. They are:
1. skeletal muscles( striated muscles)
2. smooth muscles( unstriated muscles)
3. cardiac muscles( striated and involuntary)
1. Skeletal muscles :
Organization of skeletal muscle:
a. Stripped muscles are also called skeletal muscles.
b. The entire skeletal muscle is enclosed by a sheath of fibrous connective tissue called Epimysium.
c. Each skeletal muscle consists numerous muscle fibres.
d. Each muscle fibre is surrounded by a layer of reticular fibrous tissue called Endomysium.
e. A bundle of muscle fibre is called fascicle.
f. Fascicle is surrounded by a dense connective tissue layer called perimysium.
g. A group of fascicles constitute the muscle.
h. All the connective tissue layers may extend beyond the muscle to form a chord like tendon or sheet like aponeurosis
i. Tendon serves to attach the muscle to bone.
j. These muscles contracts only according to the will of the animal. Hence these muscles are named voluntary striped muscles.
Organization of skeletal muscle fibre:
1. Skeletal muscle fibre is a long cylindrical, multinucleate cell.
2. The nuclei are oval and peripheral.
3. Each fibre is formed by the union of embryonic mononucleated myoblasts.
4. Sarcoplasm contains parallelly arranged many myofibrils.
5. Each myofibril has alternatively arranged dark and light bonds.
6. Dark and light bonds of myofibrils of muscle fibre gives striated appearance to the whole fibre.
7. Sarcoplasm contains ATP, phosphocreatine, glycogen and myoglobin etc.
8. Skeletal muscle contracts quickly and fatigue quickly.
1. Smooth muscle cells are fusiform.
2. Each cell has single nucleus in the centre.
3. Thick and thin filaments are present but they are not regularly arranged. Hence smooth muscles are unstriated.
4. It exhibit slow and prolonged contractins.
5. It remains contracted for long periods without fatigue.
6. smooth muscle is involuntary.
Cardiac Muscle( Straited and Involuntary)
1. It occurs in the wall of the heart.
2. Cardiac muscle fibres are branched forming anetwork.
3. Cardiac muscle fibre is a short cylindrical cell containing one centrally located nucleus.
4. It is striated and involuntary.
5. Cardiac muscle fibres are joined end to end by transverse thickening of plasma membrane called intercaleated discs.
6. Intercalated discs contain gap junctions and desosomes.
7. Gap junctions provide ionic continuity between adjacent cells due to which cardiac muscles acts as a functional syncytium.
8. Contraction of cardiac muscles is spontaneous, involuntary, vigorous and rhythmic.
9. Some of the cardiac muscles fibres are autorhythmic. They act as pacemakers and conducting system.
10. Cardiac muscles have almost no regenerative capacity in adults.