StructureofSkeletalMuscle for presentation.ppt

For presentation

1. Structure of
Skeletal Muscle
Presentation by: Angela Holloman

2. Introduction
•Allactivities that involve movement depend on muscles
•650 muscles in the human body
•Various purposes for muscles for:
–Locomotion
–Upright posture
–Balancing on two legs
–Support of internal organs
–Controlling valves and body openings
–Production of heat
–Movement of materials along internal tubes
•Three types of muscles in the human body
–Skeletal
–Cardiac
–Smooth

3. Skeletal Muscle
•Skeletal muscles are
muscles which are
attached to the skeleton.
•40% of human body mass
•Skeletal muscles are
mainly responsible for
locomotion, and voluntary
contractionand relaxation.

4. Structure of Skeletal muscles
•Skeletal muscles are composed of clusters of muscle
cells.
–Muscle fibers
–Myofibers
–Myocytes
•A muscle consists of packages of muscle cells called
fascicles
•A muscle cell is long and spindle shaped

5. Structure of Skeletal muscles
•Cell structure
–Muscles cells contain many nuclei
–The plasma membrane→ sarcolemma
–The cytoplasm→ sarcoplasm
–Length
–ranges from 0.1cm to more the 30cm in length
–Diameter
–ranges from 0.001cm to 0.01cm in diameter
•Myofibrils→
–elongated protein molecules
–aligned in parallel arrangements
–extend the full length of the cell.

8. Structure of Skeletal muscles
•The myofibril consists of protein
chains called myofilaments
–Myofilaments have a symmetrical,
alternating pattern of thick and thin
elements.

9. Skeletal Muscle Myosin
• Thick myofilament
• consists of a large number of bundled myosin moleculesaligned
in overlapping arrays.
• hexameric proteins with two identical heavy chains and two pairs of
different light chains.
– regulatory light chain (RLC)
– essential light chain (ELC)

10. Skeletal Muscle Actin
• The thin myofilament (F-actin, filamentous actin)
– made up of two helically intertwined chains of G-actin (globular
actin) units.
• Other proteins that bind to the actin molecules:
•Tropomyosin
•The Troponin complex→ made up of three members

12. Contraction of Skeletal Muscle
• The thick and thin filaments, along with their associated myofibril
proteins, are responsible for muscle contraction.
• How does muscle contraction work?
– Influx of calcium ions in the cell
• as a result of nerve impulses
– troponin complex pulls tropomyosin molecules away from the G-actin
subunits
– Exposure of the myosin binding sites.
– The heads of the myosin molecules can bind to the actin subunits,
forming cross bridges.
• active site in each myosin head disrupts the high-energy bond of
ATP molecules
• release of energy moves the myosin head towards the F-actin,
• when contact is made with the actin subunits, the F-actin is pulled
along, causing the myofilament to contract.
• The coordinated contraction of all the myofilaments of all the
muscle cells of a muscle, causes the entire muscle to contract.

14. Relaxation of Skeletal Muscle
–Calcium ions are carried
away from the myofilaments
–Myosin-actin linkages
loosen
–The troponin complex and
tropomyosin bind to the
myosin binding sites on the
F-actin subunits,
•Myosin and F-actin
myofilaments return to
their original positions

15. References:
•Pasternak, Jack J. Human Molecular Genetics: Mechanisms of
Inherited Diseases.Hoboken, New Jersey: John Wilkey &
Sons Inc., 2005.
•http://www.lau-verlag.de/anatom/muscleb.jpg. March, 20, 2006