Overview of the Muscle System Muscle Types pgs

Overview of the Muscle System Muscle Types pgs. 181 -185 Microscopic Anatomy of Skeletal Muscle pgs. 185 -187 *emphasis will be placed on skeletal muscle

The Muscular System • • Functions: – body movement (of any kind) – Posture/position – Stability – Generate heat – Protection Three basic muscle types: 1. Skeletal muscle 2. Cardiac muscle 3. Smooth muscle © 2015 Pearson Education, Inc.

Characteristics of Muscles • • Skeletal and smooth muscle cells are elongated (muscle cell muscle fiber) Microfilaments cause muscle contraction – Via shortening of the muscle fibers © 2015 Pearson Education, Inc.

Comparison of all three types: Skeletal ◦ ◦ ◦ Elongated Multinucleic Striated Banded Attach to skeleton Cardiac ◦ ◦ Branching One nucleus Striated Intercalated discs Gap junctions ◦ Found only in heart • Smooth -Fusiform -One nucleus -No striations -found in hollow visceral organs like stomach, bladder

Table 6. 1 Comparison of Skeletal, Cardiac, and Smooth Muscles (1 of 3) skeletal cardiac smooth

Table 6. 1 Comparison of Skeletal, Cardiac, and Smooth Muscles (3 of 3) • differences in contraction between the three types of muscle fibers: • Skeletal: has no rhythm, and the speed can vary; you control • Cardiac : has rhythm, and the rate is slow • Smooth: has variations in rhythm, depending on the process, and very slow contractions

Skeletal Muscle Characteristics � Most are attached by tendons to bones � Multinucleate � Striated—have visible banding � Voluntary—subject to conscious control © 2015 Pearson Education, Inc.

Connective Tissue Wrappings of Skeletal Muscle (from deep to superficial) • Endomysium—encloses a single muscle fiber Perimysium—wraps around a fascicle (bundle) of muscle fibers Epimysium—covers the entire skeletal muscle • Fascia—outermost layer; covers the epimysium • • – Fascia is a dense connective tissue found covering muscles, groups of muscles, and large vessels and nerves • It binds structures together like plastic wrap • Fasciitis is an inflammation of the fascia or a muscle/organ © 2015 Pearson Education, Inc.

Figure 6. 1 Connective tissue wrappings of skeletal muscle. Muscle fiber (cell) Blood vessel Perimysium Epimysium (wraps entire muscle) Fascicle (wrapped by perimysium) Endomysium (between fibers) Tendon Bone

Skeletal Muscle Attachments � Epimysium attachment blends into a connective tissue ◦ Tendons—cordlike structures �Mostly collagen fibers �Often cross a joint because of their toughness and small size ◦ Aponeuroses—sheetlike structures �Attach muscles indirectly to bones, cartilages, or connective tissue coverings © 2015 Pearson Education, Inc.

Skeletal Muscle Attachments � Sites of muscle attachment ◦ Bones ◦ Cartilages ◦ Connective tissue coverings © 2015 Pearson Education, Inc.

Microscopic Anatomy of Skeletal Muscle- looking at the muscle fiber (cell) � Sarcolemma—specialized plasma membrane ◦ Surrounds each fiber ◦ Multiple nuclei reside just beneath this membrane � Myofibrils—long organelles inside muscle cell ◦ These create Light (I) bands and dark (A) bands to give the muscle its striped appearance © 2015 Pearson Education, Inc.

Figure 6. 3 a Anatomy of a skeletal muscle fiber (cell). Sarcolemma Myofibril Light Dark Nucleus (A) band (I) band (a) Segment of a muscle fiber (cell)

Microscopic Anatomy of Skeletal Muscle � Sarcomere—contractile � The unit of a muscle fiber light and dark bands are myofilaments � They are organized in a pattern that give the muscle fiber a banded look � These are protein filaments of different widths: �Thick filaments myosin filaments �Thin filaments actin filaments © 2015 Pearson Education, Inc.

Figure 6. 3 b Anatomy of a skeletal muscle fiber (cell). Z disc H zone Z disc Thin (actin) myofilament Thick (myosin) myofilament I band A band I band Sarcomere M line (b) Myofibril or fibril (complex organelle composed of bundles of myofilaments)

What this banded pattern means: �I band light band ◦ Contains only thin filaments ◦ Z disc is only a midline interruption �A band dark band ◦ Contains the entire length of the thick filaments ◦ H zone is a lighter central area ◦ M line is in center of H zone © 2015 Pearson Education, Inc.

Figure 6. 3 b Anatomy of a skeletal muscle fiber (cell). Z disc H zone Z disc Thin (actin) myofilament Thick (myosin) myofilament I band A band I band Sarcomere M line (b) Myofibril or fibril (complex organelle composed of bundles of myofilaments)

Thick Filaments = Myosin � Composed of the protein myosin ◦ Contain ATPase enzymes ◦ Possess myosin heads ◦ Heads are known as cross bridges when they link thick and thin filaments during contraction © 2015 Pearson Education, Inc.

Thin Filaments Actin filaments � Composed of the contractile protein actin ◦ Actin is anchored to the Z disc � At rest, within the A band there is a zone that lacks actin filaments ◦ Called the H zone © 2015 Pearson Education, Inc.

Figure 6. 3 c Anatomy of a skeletal muscle fiber (cell). Sarcomere Thin (actin) myofilament Z disc M line Thick (myosin) myofilament (c) Sarcomere (contractile unit of a myofibril) H Zone Z disc

Summary of Components • • • I band: thin (light) filaments (actin) A band: thick (dark) filaments (myosin) Z disc: dark area; the boundary at each end of the sarcomere – Actin attaches at the Z disc (a network of proteins) • • H zone: central part of A band where no thin filaments occur M line: center of the H zone – Myosin attaches to the M line via protein rods

Sarcoplasmic reticulum (SR) • Specialized smooth endoplasmic reticulum • Stores and releases calcium • Surrounds the myofibril in a tubule arrangement © 2015 Pearson Education, Inc.