Animal physiology and anatomy muscular system

Muscle is a soft tissue found in most animals.
They are primarly responsible for maintaining and changing posture,locomotion as well as movement of internal organs.
They are derived from the mesodermal layer of embryonic germ cells in a process known as myogenesis.
Based on locomotion three types of muscles are identified.

1. Muscular system

2. Muscle is a soft tissue found in most animals. They are primarly responsible for maintaining and changing posture,locomotion as well as movement of internal organs. They are derived from the mesodermal layer of embryonic germ cells in a process known as myogenesis. Based on locomotion three types of muscles are identified. They are MUSCLE

3. Muscles 1.Striated muscle 2.Non-striated muscle 3.Cardiac muscle

4. Striated muscle Striated muscles are closely associated with skeletal components. So it is called skeletal muscle. They are voluntary in nature. Non-striated muscle Non-striated muscles are located in the inner walls of hollow visceral organs of body like alimentary canal,reproductive tract etc. They do not exhibit any striation and are smooth in appearance. So they are called smooth muscles. Cardiac muscle Cardiac muscles are the muscles of heart. They are striated and involuntary in nature.

5. Ultra structure of skeletal muscle Each muscle cell is called muscle fibre . Each muscle fibre is surrounded by endomysium . ------- E ndomysium Muscle fibre 2.A group of muscle fibres bundled to gether by collagen to form fasciculi or fascicle . 3.Each fascicle is surrounded by perimysium .

6. All the fascicle collectively form the the muscle belly. Each muscle belly is surrounded by a connective layer called epimysium .

7. The plasma membrane of the muscle fibre is called sarcolemma and the cytoplasm is called sarcoplasm . The sarcoplasm contains numerous protein filaments are called myofibrils. Each myofibril contains thin filament actin and thick filament myosin. Myofibril is surrounded by network of tubules and channels called sarcoplasmic reticulum . The calcium stored in this area.

8. Actin Actin is a fibrous protein. It is an insoluble protein. It exists in two forms,namely G- actin and F- actin G- actin is the globular actin . It is spherical in shape. F – actin is the filamentous actin . It is in the form of a double helix.

9. In the resting muscles,the actin remains in the form of G- actin . During muscle contraction, the G- actin becomes F- actin . During muscle contraction,actin combines with myosin to form actomyosin . actin +myosin --------  actomyosin Myosin Myosin is a fibrous protein. It is an insoluble protein. It is in the form of golf stick . It consists of rode like- head,neck and tail regions. The head is also called cross bridge as it attaches with the actin during muscle contraction.

10. Diagram showing myosin filament. ATP = Adenosine triphosphate .

11. Tropomyosin and T roponin Tropomyosin and troponin are the two main proteins that regulate actin and myosin interactiions . Tropomyosin is a long strand that twisted around F- actin filament and prevents muscle contraction. Troponin is distributed in regular intervals on the surface of tropomyosin .

12. SARCOMERE A sarcomere is the basic unit of skeletal muscle tissue. It is made up of central dark band and two half light bands. The two half light bands are firmly attached to the Z line . The region of the dark band represents H zone.

13. The light band contains actin and it is called I band or Isotropic band. The dark band contains myosin and it is called A band or Anisotropic band. The actin is a thin filament and myosin is a thick filament.

14. MECHANISM OF MUSCLE CONTRACTION The mechanism of muscle contraction is best explained by sliding filament theory. This theory was proposed by Huxley and Hanson in 1957. It states that the contraction of muscle fibre takes place by the sliding of the thin filament over the thick filaments. Mechanism 1.An action potential is originating in the central nervous system(CNS) and reach as to the alpha motor neuron. 2.The junction between alpha motor neuron and sarcolemma of the muscle fibre is called neuromuscular junction or motor end plate.

15. 3.The neural signal reaching this junction and releases a chemical called acetyl choline . It leads to the depolarisation of motor end plate. 4.It spreads through the muscle fibre and releases calcium ions from sarcoplasmic reticulum. 5.The calcium binds with troponin on actin filament. It allows the movement of tropomyosin . 6.Utilising the energy from ATP hydrolysis, the head of myosin bind active sites on actin and form a cross bridge and causes muscle contraction. 7.The ATP molecule split again and myosin head is reactivated for the next cycle to begin.

16. Diagram showing power stroke by myosin head. Stage 1: Myosin head binds with actin ; Stage 2: Tilting of myosin head (power stroke) drags the actin filament.

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