1. Physiology, drugs and disease Muscle Structure and Function FdSc FISM Year 2 Janis Leach 15/01/10

2. Objectives Define 3 types of muscle tissue Define 3 types of muscle tissue Describe the functions of muscle Describe the functions of muscle Outline the structure of muscle Outline the structure of muscle Explain the sliding filament theory Explain the sliding filament theory

3. Types of muscle tissue Skeletal muscle Skeletal muscle Voluntary muscles – attachments to bones Voluntary muscles – attachments to bones Cardiac muscle Cardiac muscle Involuntary muscle only present in the heart Involuntary muscle only present in the heart Smooth muscle Smooth muscle Involuntary muscle found in walls of hollow organs Involuntary muscle found in walls of hollow organs

4. Functions Movement Movement Skeletal muscle contracts and exerts force on the skeletal system Skeletal muscle contracts and exerts force on the skeletal system Cardiac muscle allows the pressure to pump blood around the body Cardiac muscle allows the pressure to pump blood around the body Smooth muscle in the walls of blood vessels maintains BP Smooth muscle in the walls of blood vessels maintains BP

5. Functions Postural maintenance Postural maintenance Skeletal muscles maintain posture Skeletal muscles maintain posture Joint Stability Joint Stability Skeletal muscles contribute to joint stability Skeletal muscles contribute to joint stability Heat Generation Heat Generation Muscles produce heat during contraction Muscles produce heat during contraction Critical in maintaining normal body temperature Critical in maintaining normal body temperature

6. Structure of muscle

7. Structure Epimysium Epimysium Whole muscle wrapped in connective tissue Whole muscle wrapped in connective tissue Fascicles Fascicles Bundles of muscle cells Bundles of muscle cells Perimysium Perimysium Surrounds the bundles Surrounds the bundles Endomysium Endomysium Each muscle fibre surrounded by sheath of tissue – gives strength and elasticity Each muscle fibre surrounded by sheath of tissue – gives strength and elasticity

8. Muscle cell Skeletal muscle cells are very large compared to other cells Skeletal muscle cells are very large compared to other cells Muscle cells or fibers are long cylindrical cells with multiple oval nucleui arranged just below the sarcolemma or plasma membrane. Muscle cells or fibers are long cylindrical cells with multiple oval nucleui arranged just below the sarcolemma or plasma membrane. Myofibrils (contractile elements of the muscle cell) Myofibrils (contractile elements of the muscle cell)

9. Muscle cell Note the alternating dark and light bands in the muscle fiber that consist of even smaller contractile units called sarcomeres (muscle segemen). The sarcomere is the smallest contractile unit of a muscle fiber Note the alternating dark and light bands in the muscle fiber that consist of even smaller contractile units called sarcomeres (muscle segemen). The sarcomere is the smallest contractile unit of a muscle fiber

10. Myofibrils thick filament  myosin thick filament  myosin thin filament  actin thin filament  actin Myosin - Each filament within a scaromere contains  200 myosin molecules. Myosin - Each filament within a scaromere contains  200 myosin molecules. Actin - Also has several regulatory proteins Actin - Also has several regulatory proteins

11. Sliding filament theory Huxley’s sliding filament theory of muscle contraction Muscle cells shorten because their sarcomeres shorten. As the length of the sarcomeres shortens, the myofibrils shorten resulting in a shortening of the cell as a whole. Muscle cells shorten because their sarcomeres shorten. As the length of the sarcomeres shortens, the myofibrils shorten resulting in a shortening of the cell as a whole. The thick or thick filaments do not change length during shortening. The thick or thick filaments do not change length during shortening.

12. Sliding filament theory As name of the theory suggests the change in the length of the sarcomere is due to the sliding of the filaments. As name of the theory suggests the change in the length of the sarcomere is due to the sliding of the filaments. The overlap of the thick and thin filaments changes during shortening with the thin filaments sliding toward the centre of the sarcomere. The overlap of the thick and thin filaments changes during shortening with the thin filaments sliding toward the centre of the sarcomere.

14. During contraction the cross-bridges between the myosin and actin filaments pull them towards one another this increases the overlap and pulls the Z lines towards one another. Contraction of skeletal muscle

15. Motor unit Consists of motor neuron and all the muscle fibres that it supplies Consists of motor neuron and all the muscle fibres that it supplies It is the functional unit of skeletal muscle It is the functional unit of skeletal muscle 1 motor unit can supply 2000 muscle fibres 1 motor unit can supply 2000 muscle fibres Precise movements – 1 unit will supply 2 or 3 fibres Precise movements – 1 unit will supply 2 or 3 fibres Non precise – 1 will supply hundreds Non precise – 1 will supply hundreds A single motor unit will cause weak contraction of the entire muscle. A single motor unit will cause weak contraction of the entire muscle.

16. Task Describe the sliding filament theory in your own words Describe the sliding filament theory in your own words Explain what a motor unit is Explain what a motor unit is