• Skeletal – attached to bone• Cardiac – found in the heart• Smooth – lines hollow organs

Three types of muscle

• Produce skeletal movement• Maintain posture and body position• Support soft tissues• Guard entrances and exits• Maintain body temperature

Skeletal muscle functions

• 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

Organization of connective tissues

Figure 10.1

Figure 10.1 The Organization of Skeletal Muscles

• 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

Skeletal muscle fibers

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 contractionSarcomeres – regular arrangement of myofibrils

Skeletal muscle fibers cont.

Figure 10.3

Figure 10.3 The Structure of a Skeletal Muscle Fiber

• 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

Sarcomeres

- 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

Sarcomeres cont.

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

Figure 10.4 Sarcomere Structure, Part I

Figure 10.4

Figure 10.5 Sarcomere Structure, Part II

Figure 10.5