1. Three types of muscle Skeletal – attached to bone
Cardiac – found in the heart
Smooth – lines hollow organs

2. Skeletal muscle functions
Produce skeletal movement
Maintain posture and body position
Support soft tissues
Guard entrances and exits
Maintain body temperature

3. Organization of connective tissues
Epimysium- collagen fibers that surrounds muscle
covers individual muscle fibers
Perimysium- a connective tissue partition that separate adjacent fasciculi in a skeletal muscle
Fasciculus- a small bundle; usually refers to a collection of muscle fibers or nerve axons
Epimysium and perimysium contain blood vessels and nerves
Endomysium- surrounds individual fibers; satellite (stem) cells between
Tendons, or aponeuroses, attach muscle to bone or muscle

4. Figure 10.1 The Organization of Skeletal Muscles

5. Skeletal muscle fibers
Sarcolemma- plasma membrane; surrounds sarcoplasm; invaginates to form Transverse (T) tubules
T tubules- narrow tubes that are continuous with the sarcolemma and extend into the sarcoplasm at right angles to the cell surface
Sarcoplasm- muscle cell cytoplasm

6. Skeletal muscle fibers cont.
Sarcoplasmic reticulum (SR)- modified ER; located near T tubules; surround myofibrils
- SR store and release Ca2+
- Calsequestrin within binds Ca2+
- Myofibril- Organized collections of myofilaments in skeletal and cardiac muscle cells
- surrounded by mitochondria and glycogen
- thick and thin filaments
- organized regularly
T-tubules and myofibrils aid in contraction
Sarcomeres – regular arrangement of myofibrils

7. Figure 10.3 The Structure of a Skeletal Muscle Fiber

8. Sarcomeres
Sarcomers- repeating functional units of myofibrils (n=10,000/fibril)
Has alternating A (dark) and I bands
A Band- The thick filaments are located at at the center of the sarcomere (i.e width of thick filament)
center is the M line
H zone- lighter region on either side of the M line
has thick, but no thin, filaments

9. Sarcomeres cont.
- I Band- only thin filaments and extends from A band of one sarcomere to A band of next sarcomere
- centered by Z line (striation)
- separates sarcomeres
- its actinins (protein) join filaments of sarcomeres; titin
(protein) attaches thick filaments to Z lines
Thin filaments: F actin- double twisted strand of G actin
(protein); held together by nebulin
- Tropomyosin covers active sites
- Troponin- binds one of its three globular subunits to tropomyosin,
creating a troponin-Tropomyosin complex
- second subunit binds to one G actin (holds complex together)
- third subunit has a receptor that binds one Ca2+ ion

10. Sarcomeres cont.
Thick filaments- A cytoskeletal filament in a skeletal or
cardiac muscle
- composed of myosin (protein) with a core of titin
- myosin molecules have elongate tail, globular head
- heads form cross-bridges during contraction
- interactions between G-actin and myosin prevented by tropomyosin during rest

11. Figure 10.4 Sarcomere Structure, Part I

12. Figure 10.5 Sarcomere Structure, Part II