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