Question

The fate of acetylcholine TOITUWING DAY 10. Describe skeletal muscle fiber contraction including: The sliding filament mechanism Excitation-contraction coupling The cross bridge cycle How muscle fiber contraction results in body movement 11 Describe skeletal muscle fiber relaxation and the resulting relaxation of an entire veletal . SPORTION IS NONNESOTIABLE UN NEGOTIABLE SARONNON NEGOTIABL 14. Define the two abnormal contractions of skeletal muscles, cramp and spasm. 15. Describe muscle tone and state its importance to the health of the muscular system.

Answer 1

Muscle is a specialized tissue of mesodermal origin.About 40-50 percent of the body weight of human adult.skeletal muscles are primarily involved in locomotive actions and bringing in changes in body postures.

Ultrastructure of a skeletal muscle fibre:Each muscle fibre is lined by the plasma enclosing the sarcoplasm.Skeletal muscle fibre is a syncytinum,as each fiver is formed by fusion of embryonic,mononucleate myoblasts,hence the skeletal muscle cells are multinucleate,with characteristically peripheral nuclei.The endoplasmic reticulum,also called sarcoplasmic reticulum of the muscle fibers is the store house of calcium ions.A characteristic feature of the muscle fiber is the presence of a large number of parallel filaments called myofilaments or myofibrils ,in the sarcoplasm.  

Mechanism of muscle contraction:

It was explained by the sliding filament theory,It states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments .It was proposed by Jean Hanson and Hugh Huxley .Muscle contraction steps.

• Excitation of muscle
• Formation of cross bridges
• Power stroke
• Recovery stroke
• Relaxation of muscle.

Excition-contraction coupling : It describes rapid communication between skeletal muscle and calcium ions release into SR which lead to contraction.

The cross bridge cycle: when myosin heads hydrolysis ATP into ADP and Pt,the conformation of the myosin is changed to an active state so that it can perform the power stroke.when myosin head bind to actin it releases P1 and undergoes another conformational change,pulling the thin filaments towards the center of the A band ,thus the power stroke is completed and the myosin head releases the ADP. At the end of the power stroke,the myosin head binds to a new molecule of ATP, which displaced it from act in.this process is called cross bridge cycle.

Muscle cramp&spasms:sudden and involuntary contraction of muscle is a spasm whereas cramp means more muscles involuntary contraction.

• For to locomotion of a living organisms
• For To maintain body posture