Three types of muscle
• Skeletal – attached to bone
• Cardiac – found in the heart
• Smooth – lines hollow organs
Skeletal muscle functions
•
•
•
•
•
Produce skeletal movement
Maintain posture and body position
Support soft tissues
Guard entrances and exits
Maintain body temperature
Organization
of connective
• Epimysiumcollagen fibers
that surrounds muscle
tissues
– 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
Figure 10.1 The Organization of
Skeletal Muscles
Figure 10.1
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
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
Figure 10.3 The Structure of a
Skeletal Muscle Fiber
Figure 10.3
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
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
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