Chapter 9: Muscles and Muscle Tissue

Governor Arnold Schwarzenegger

Muscle Functions Producing Movement Maintaining Posture Stabilizing Joints Generating Heat

3 Types of Muscle Skeletal Muscle Cardiac Muscle Smooth Muscle

Skeletal Muscle attaches to bones which form levers used for bodily movement

Cardiac Muscle forms the heart used to pump blood through circulatory system

Smooth Muscle lines gut and blood vessels controls diameter of these tubes and in gut helps to propel the digested food

Cells Connected by Intercalated Discs or Gap Junctions?  Property  Skeletal Muscle  Cardiac Muscle  Smooth Muscle  Striations?  Yes Yes  No  Nuclei per Cell  Many  Single  Cells Connected by Intercalated Discs or Gap Junctions?

Relative Speed of Contraction  Property  Skeletal Muscle  Cardiac Muscle  Smooth Muscle  Relative Speed of Contraction Fast   Intermediate  Slow  Voluntary Control? Yes  No No  Control of Contraction  Nerves  Beats spontaneously but modulated by nerves  Nerves Hormones Stretch

Muscle cells Large, long cells called FIBERS Contain two types of proteins--actin and myosin Excitable (irritable), contractile, extensible, and elastic Myo-, mys, or Sarco code for muscle

Skeletal Muscle Anatomy Rich blood supply to center of muscle, branch to capillaries sheathing cells Rich nerve supply, branching into each muscle, ending one branch to each muscle fiber

Structure of Skeletal Muscle Cigar shaped, multinucleate cells Packed with myofilaments made of actin and myosin creating visible bands (striations) Varied length, may be over a foot long

Structure cont. Surrounded by dense, fibrous Connective tissue (CT) sheaths Endomysium around each fiber Perimysium around bundles of fibers (fascicles) Epimysium around all fascicles

Figure 6. 1 Connective tissue wrappings of skeletal muscle Figure 6.1 Connective tissue wrappings of skeletal muscle. © 2000  The Benjamin/Cummings Publishing Company

Microscopic structure Muscle fibers filled with Sarcoplasm Glycogen and myoglobin Nuclei pushed to the edge of sarcolemma by long protein strands that run length of the cell, myofibrils Composed of contractile units, sarcomeres, made of myofilaments

Figure 6. 3 Anatomy of a skeletal muscle cell (fiber) Figure 6.3 Anatomy of a skeletal muscle cell (fiber). (a) A portion of a muscle fiber. One myofibril has been extended. (b) Enlarged view of a myofibril showing its banding pattern. (c) Enlarged view of one sarcomere (contractile unit) of a myofibril. (d) Structure of the thick and thin myofilaments found in the sarcomeres. © 2000  The Benjamin/Cummings Publishing Company

Myofilaments Two types--actin and myosin -Filaments are clusters of actin and myosin Actin forms thin filaments Myosin forms thick filaments

Sarcomere structure Alternating dark and light bands Lateral dark bands--A-band End in light I-bands, with Z-line in center marking joint with next sarcomere on each side

Muscle Contraction Sarcomere - basic unit of muscle contraction Skeletal and cardiac muscle are striated The striations are caused by alignment of bands: the most prominent are the A and I bands and the Z line The unit between 2 Z lines is called the sarcomere

Muscle Contraction-Sarcomere In the A band the 2 proteins overlap The I band contains only the actin protein When muscle contracts the sarcomere shortens and the Z lines move closer together

Muscle Contraction-relaxed state When Muscle Contracts Protein Filaments Slide Together Thin filaments: actin, attached to Z line, found in both A and I bands Thick filaments: myosin, found in A band Relaxed state:

Muscle Contraction-Contracted state When muscle contracts the actin filaments slide into the A band, overlapping with myosin

Muscle Contraction-Contracted state Notice what happens when muscle contracts: a) the Z lines move closer together b) the I band becomes shorter c) the A band stays at the same length This is called the "sliding filament" model of muscle contraction

Muscle Contraction-Crossbridge The filaments slide together because myosin attaches to actin and pulls on it myosin head(H) attaches to actin filament (A), forming a crossbridge After the crossbridge is formed the myosin head bends, pulling on the actin filaments and causing them to slide:

Actin Molecule