An Introduction to Muscle Tissue A primary tissue

An Introduction to Muscle Tissue § A primary tissue type, divided into § Skeletal muscle § Cardiac muscle § Smooth muscle

An Introduction to Muscle Tissue § Skeletal Muscles § Are attached to the skeletal system § Allow us to move § The muscular system § Includes only skeletal muscles

Functions of Skeletal Muscles § Produce skeletal movement § Maintain body position § Support soft tissues § Guard openings § Maintain body temperature § Store nutrient reserves

Skeletal Muscle Structures § Muscle tissue (muscle cells or fibers) § Connective tissues § Nerves § Blood vessels

Skeletal Muscle Structures § Organization of Connective Tissues § Muscles have three layers of connective tissues § Epimysium: – exterior collagen layer – connected to deep fascia – Separates muscle from surrounding tissues § Perimysium: – surrounds muscle fiber bundles (fascicles) – contains blood vessel and nerve supply to fascicles § Endomysium: – surrounds individual muscle cells (muscle fibers) – contains capillaries and nerve fibers contacting muscle cells – contains myosatellite cells (stem cells) that repair damage

Skeletal Muscle Structures Figure 10– 1 The Organization of Skeletal Muscles.

Skeletal Muscle Structures § Organization of Connective Tissues § Muscle attachments § Endomysium, perimysium, and epimysium come together: – at ends of muscles – to form connective tissue attachment to bone matrix – i. e. , tendon (bundle) or aponeurosis (sheet)

Skeletal Muscle Structures § Nerves § Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord) § Blood Vessels § Muscles have extensive vascular systems that § Supply large amounts of oxygen § Supply nutrients § Carry away wastes

Skeletal Muscle Fibers § Are very long § Develop through fusion of mesodermal cells (myoblasts) § Become very large § Contain hundreds of nuclei

Skeletal Muscle Fibers Figure 10– 2 The Formation of a Multinucleate Skeletal Muscle Fiber.

Skeletal Muscle Fibers Figure 10– 2 a The Formation of a Multinucleate Skeletal Muscle Fiber.

Skeletal Muscle Fibers Figure 10– 2 b The Formation of a Multinucleate Skeletal Muscle Fiber.

Skeletal Muscle Fibers § Internal Organization of Muscle Fibers § The sarcolemma § The cell membrane of a muscle fiber (cell) § Surrounds the sarcoplasm (cytoplasm of muscle fiber) § A change in transmembrane potential begins contractions

Skeletal Muscle Fibers § Internal Organization of Muscle Fibers § Transverse tubules (T tubules) § Transmit action potential through cell § Allow entire muscle fiber to contract simultaneously § Have same properties as sarcolemma

Skeletal Muscle Fibers § Internal Organization of Muscle Fibers § Myofibrils § Lengthwise subdivisions within muscle fiber § Made up of bundles of protein filaments (myofilaments) § Myofilaments are responsible for muscle contraction § Types of myofilaments: – thin filaments: » made of the protein actin – thick filaments: » made of the protein myosin

Skeletal Muscle Fibers § Internal Organization of Muscle Fibers § Sarcoplasmic reticulum (SR) § A membranous structure surrounding each myofibril § Helps transmit action potential to myofibril § Similar in structure to smooth endoplasmic reticulum § Forms chambers (terminal cisternae) attached to T tubules

Skeletal Muscle Fibers § Internal Organization of Muscle Fibers § Triad § Is formed by one T tubule and two terminal cisternae § Cisternae: – concentrate Ca 2+ (via ion pumps) – release Ca 2+ into sarcomeres to begin muscle contraction

Skeletal Muscle Fibers Figure 10– 3 The Structure of a Skeletal Muscle Fiber.

Skeletal Muscle Fibers § Internal Organization of Muscle Fibers § Sarcomeres § The contractile units of muscle § Structural units of myofibrils § Form visible patterns within myofibrils § Muscle striations § A striped or striated pattern within myofibrils: – alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

Skeletal Muscle Fibers § Internal Organization of Muscle Fibers § Sarcomeres § M Lines and Z Lines: – M line: » the center of the A band » at midline of sarcomere – Z lines: » the centers of the I bands » at two ends of sarcomere

Skeletal Muscle Fibers § Internal Organization of Muscle Fibers § Sarcomeres § Zone of overlap: – the densest, darkest area on a light micrograph – where thick and thin filaments overlap § The H Band: – the area around the M line – has thick filaments but no thin filaments

Skeletal Muscle Fibers § Internal Organization of Muscle Fibers § Sarcomeres § Titin: – are strands of protein – reach from tips of thick filaments to the Z line – stabilize the filaments

Skeletal Muscle Fibers Figure 10– 4 a Sarcomere Structure.

Skeletal Muscle Fibers Figure 10– 4 b Sarcomere Structure.

Skeletal Muscle Fibers Figure 10– 5 Sarcomere Structure.

Skeletal Muscle Fibers Figure 10– 6 Levels of Functional Organization in a Skeletal Muscle.

Skeletal Muscle Fibers Figure 10– 6 Levels of Functional Organization in a Skeletal Muscle.

Skeletal Muscle Fibers § Sarcomere Function § Transverse tubules encircle the sarcomere near zones of overlap § Ca 2+ released by SR causes thin and thick filaments to interact

Skeletal Muscle Fibers § Muscle Contraction § Is caused by interactions of thick and thin filaments § Structures of protein molecules determine interactions

Skeletal Muscle Fibers § Four Thin Filament Proteins § F-actin (Filamentous actin) § Is two twisted rows of globular G-actin § The active sites on G-actin strands bind to myosin § Nebulin § Holds F-actin strands together § Tropomyosin § Is a double strand § Prevents actin–myosin interaction § Troponin § A globular protein § Binds tropomyosin to G-actin § Controlled by Ca 2+

Skeletal Muscle Fibers Figure 10– 7 a, b Thick and Thin Filaments.

Skeletal Muscle Fibers § Initiating Contraction § Ca 2+ binds to receptor on troponin molecule § Troponin–tropomyosin complex changes § Exposes active site of F-actin

Skeletal Muscle Fibers § Thick Filaments § Contain twisted myosin subunits § Contain titin strands that recoil after stretching § The mysosin molecule § Tail: – binds to other myosin molecules § Head: – made of two globular protein subunits – reaches the nearest thin filament

Skeletal Muscle Fibers Figure 10– 7 c, d Thick and Thin Filaments.

Skeletal Muscle Fibers § Myosin Action § During contraction, myosin heads § Interact with actin filaments, forming cross-bridges § Pivot, producing motion