Muscle Types pgs Microscopic Anatomy of Skeletal Muscle pgs *emphasis will be placed on skeletal muscle

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.

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.

 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

skeletalcardiacsmooth

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

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

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.

Blood vessel Perimysium Muscle fiber (cell) Fascicle (wrapped by perimysium) Endomysium (between fibers) Tendon Bone Epimysium (wraps entire muscle)

 Epimysium blends into a connective tissue attachment ◦ 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.

 Sites of muscle attachment ◦ Bones ◦ Cartilages ◦ Connective tissue coverings © 2015 Pearson Education, Inc.

 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 6.3a Anatomy of a skeletal muscle fiber (cell). Sarcolemma Myofibril NucleusDark (A) band Light (I) band (a) Segment of a muscle fiber (cell)

 Sarcomere—contractile unit of a muscle fiber  The 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 6.3b Anatomy of a skeletal muscle fiber (cell). Z disc H zone Thin (actin) myofilament Thick (myosin) myofilament Myofibril or fibril (complex organelle composed of bundles of myofilaments) I band A band M lineI band Sarcomere (b)

 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.

Z disc H zone Thin (actin) myofilament Thick (myosin) myofilament Myofibril or fibril (complex organelle composed of bundles of myofilaments) I band A band M lineI band Sarcomere (b)

 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.

 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 6.3c Anatomy of a skeletal muscle fiber (cell). Thin (actin) myofilament Thick (myosin) myofilament Sarcomere (contractile unit of a myofibril) Z disc M line Z disc Sarcomere (c) H Zone

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.