Post on 13-Aug-2020
Muscle Physiology 2Dr. Sumera Gul
Associate Professor
Department of Physiology
Learning Objectives:
At the end of the lecture the students should be able to:
• Explain the physiological functioning of different components of sarcomere
• Explain the different phases of skeletal muscle contraction
• Describe the ionic and chemical basis of skeletal muscle contraction
Review of previous lecture
Review
• Functions of muscles
• Types of muscles
• Basic characteristics of muscles
• Muscles
• Fasciculus
• Muscle fiber
• Muscle spindle
• Sarcomere
• Actin, Myosin, Titin
Actin
• Light chains
• F-actin chains
• Made of polymerized G- Actin molecules
• 1 ADP is attached to each G-actin
Tropomyosin
• Present on the actin molecule
• They are spirally wrapped around F actin helix
• In resting state they cover the active sites to prevent contraction
Troponin
• Present along the side of the tropomyosin
• They are a complex of 3 loosely bound proteins
• Troponin I
• Troponin C
• Troponin T
Actin
Myosin Molecule
• 480,000
• 2 heavy chains: 200,000
• 4 lights chains: 20,000
Myosin
• Flexible at hinge and the attachment of head
• Head acts as ATPase enzyme
• Have sites for attachment of Actin and ATP
• Cross bridge
Mechanism of Skeletal Muscle Contraction
Sliding Filament Mechanism of Muscle Contraction
Cross-bridge interaction betweenactin and myosin brings aboutmuscle contraction by means ofthe sliding filament mechanism.
Sliding Filament Model :
• Actin myofilaments sliding over myosin to shorten sarcomeres• Actin and myosin DO NOT change length
• Shortening sarcomeres responsible for skeletal muscle contraction
• During relaxation, sarcomeres lengthen
Walk Along or Rachet Theory
Sequence of Events