1. Muscular Contraction

2. Characteristics of Muscles
Muscle fibres are elongated
Contraction of muscles is due to the movement of microfilaments
All muscles share some terminology:
Prefix myo refers to muscle
Prefix mys refers to muscle
Prefix sarco refers to flesh

3. Skeletal Muscle Characteristics
Most are attached by tendons to bones
Cells are multinucleate
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by connective tissue

4. Connective Tissue Wrappings of Skeletal Muscle
Endomysium = around single muscle fibre
Perimysium = around a fascicle (bundle) of fibres

5. Connective Tissue Wrappings of Skeletal Muscle
Epimysium = covers the entire skeletal muscle
Fascia = on the outside of the epimysium

6. Gross Structure of Skeletal Muscle
Skeletal muscles are encased by epimysium: fascia of fibrous connective tissue.
A bundle of cylindrical muscle fibres is surrounded by the perimysium.
Endomysium surrounds each muscle fibre.
Sarcolemma beneath endomysium is a thin, elastic membrane.
epi: on; peri: around; endo: inner

8. Microscopic Anatomy of Skeletal Muscle
Cells are multinucleate
Nuclei are just beneath the sarcolemma

9. Microscopic Anatomy of Skeletal Muscle
Sarcolemma – specialized plasma membrane
Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum (network of membranous tubules within the cytoplasm )

10. Sarcoplasm (cytosol) is the fluid portion in muscle fibres.
Contains contractile proteins, nuclei, mitochondria, sarcoplasmic reticulum.

11. Microscopic Anatomy of Skeletal Muscle
Myofibril
Bundles of myofilaments
Myofibrils are aligned to give distinct bands
I band =
light band
A band = dark band

12. Muscle Structure Each myofibril is made up of parallel filaments.
There are 2 kinds of filament called thick & thin filaments.
These 2 filaments are linked at intervals called cross bridges, which stick out from the thick filaments

13. Microscopic Anatomy of Skeletal Muscle
Sarcomere
Contractile unit of a muscle fibre

14. Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere:
Thick filaments = myosin filaments
Composed of the protein myosin
Has ATPase enzymes

15. Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere
Thin filaments = actin filaments
Composed of the protein actin

16. Distinguished area between Z lines.
Thicker filaments confined to A band, a lighter middle region called the H zone.
Thinner filaments arise in middle region of I band, at the Z line.
During contraction, neither thick nor thin filaments change in length. They slide.

17. Microscopic Anatomy of Skeletal Muscle
Myosin filaments have heads (extensions, or cross bridges)
Myosin and actin overlap

18. Microscopic Anatomy of Skeletal Muscle
At rest, there is a bare zone that lacks actin filaments
Sarcoplasmic reticulum (SR) – for storage of calcium

19. Sarcomere
H zone
A band
I band