Using IT, determine the indicated property for each case in 6.4. Compare the values obtained using the software with the tabular values and discuss.
Muscle Tissues Muscle belly: grossly visible muscle, consists of billions of myofibers Muscle fascicle: grossly visible thread of muscle belly Myofiber: = individual muscle cell, = muscle fiber, bag that holds a clump of angel hair pasta, multinucleated, nuclei located immediately underneath the cell membrane, extends from the origin to the insertion Myofibril: contractile substance that fills the myofiber, looks like a clump of angel hair pasta, extends from the origin to the insertion Myofilament: protein structure that makes up the contractile element of a muscle cell, one strand of angel hair pasta 2 types – myosin and actin Myofilaments (myosin and actin) makes a myofibril. Myofibrils form a myofiber. Myofibers forms a muscle fascicle. Muscle fascicles form the muscle belly 3 Types of Muscle Cardiac (striated) Smooth Skeletal (striated) Fibrous Connective Tissue of Muscle Epimysium: outer layer, rind of a grapefruit, loose and irregular dense CT Perimysium: surrounds fascicles (divide muscle into pieces), spokes of CT that poke into fascicles, irregular dense CT Endomysium: subunit of perimysium, collagen fibers attach to myofiber plasma membrane All collagen fibers distributed thoughout these three layers are collected at the end of the muscle to form a tendon Motor Unit Neuron attaches to every myofiber If the attachment is destroyed, there is a loss of innervation to those myofibers and they die (loss of muscle mass) Motor units = one efferent somatic motor neuron and all the muscle fibers innervated by the neuron. o Can have 1 neuron per 2-3 myofibers – fine muscle control like that needed in the iris o Can have 1 neuron per 1000 myofibers – course muscle control like that needed in quadriceps to counteract gravity Sarcolemma: plasma membrane of a myofiber Sarcoplasm: cytoplasm of a myofiber Sarcomere: functional contractile unit of a muscle fiber Sarcoplasmic Reticulum: meshwork, contains Ca2+, ends are cisterna 2 cisterna + 1 t-tubule = triad SKELETAL MUSCLE!! Sarcomere = contractile unit, arranged side by side down a myofibril o During contraction, sarcomeres shorten by drawing the two ends towards the middle Myofibril Arrangement (1 sarcomere depicted) Myosin o Pink o Heavy chains o Appearance of a golf club at the molecular level with the heads at the ends and the handles tied together in the middle o Heads can flex and are energy dependent o Heads bind to sites on the actin filaments Actin o Green o Protein that has a globular structure o Interdigitating the myosin heavy chains o Alpha-actinin Holds actin together within their chains Anchors actin at the end of the sarcomere Also joins sarcomeres together by attaching the ends of actins together Ends are “welded” together down the length of the myofibril o Tropomyosin: protein wrapped around actin filaments Troponin C: protein attached to tropomyosin Rigid arrangement of myofilaments within the myofibril o Gives the myofibril the pattern of cross-striations Z-band: end of a sarcomere, where actin filaments from two sarcomeres are welded together end-to-end A-band: fill length of myosin heavy chains (golf club head to golf club head) M- band: where myosin is covalently linked together H-band: two free ends of actin filament across myosin filament A-band: length of myosin I-band: end of one myosin filament to the end of the end of another myosin filament (includes Z band) Contraction Actin moves inward Z-bands brought closer together thanks to the actin H and I band shortens M and A band not affected Steps o In the resting state, the tropomyosin is positioned on the actin filament to cover all the binding sites of the myosin heads Myosin cannot yet bind to actin Positive on the outside, negative on the inside of the cell Excitation reverses these charges o Electrical charge/stimulus down the nerve to the motor end plate o Release of acetylcholine into sarcolemma o Electrical stimulus spread across sarcolemma and into t-tubule o Electrical charge jumps to sarcoplasmic reticulum o Release of Ca2+ from sarcoplasmic reticulum o Calcium binds to troponin C o Structure of troponin C changes so drastically that the tropomyosin changes its location just slightly along the actin filament o Myosin binding sites on the actin filament are exposed o Myosin heads flex, ratcheting the actin down the myosin towards the M-band o Once energy is released, the myosin heads relax, let go of the actin filaments, and everything returns to its resting state Ca2+ reabsorbed into sarcoplasmic reticulum Ca2+ originally comes from from bone in cutting cone CARDIAC MUSCLE Myofibers branch Myofibers are attached together end-to-end Intercalated Disc: site where they are attached, morphologically observable o Desmosomes (aka macula adherens), fascia adherens Lipid structures Myofibrils that fill each cell are attached to intercalated discs between the cells Shorten, tugging on the intercalated disc, tugging on the next myofiber, contracting the muscle No nerve motor end plates on cardiac cells One cells excites another cell and so on Act as a mechanical and electrical group because intercalated discs Gap Junction Area of sarcolemma that is full of protein instead of lipid Electrical charge travels faster through polarized proteins than lipid fats Low electrical resistance Plasmalemma T-tubules – channels through the myofiber Sarcolemma Myofiber Myofilaments Smooth muscle in ring shapes