Solved: Using IT, determine the indicated property for

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