BIO 446L 1st Edition Lecture 9 Outline of Last Lecture I. Exam Review and ExamOutline of Current Lecture I. Muscle Tissuea. Muscle tissue types and innervationb. Skeletal musclei. developmentii. organizationc. Cardiac musclei. Organizationii. Anatomy of cardiac muscled. Smooth musclei. Anatomy of smooth muscleCurrent LectureMuscle Tissue- Muscle tissue typeso Skeletal muscle—innervated by somatic motor neurons Voluntary Long cells Multiple nuclei in periphery- Due to actin and myosin taking up space Striated—due to sarcomereo Cardiac muscle—innervated by autonomic neurons Involuntary Striated (not as regularly as skeletal)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Intercalated disk junctions are unique to cardiac muscle Cells are long, like skeletal, but are branchedo Smooth muscle—innervated by autonomic neurons Involuntary Irregular actin/myosin inside cells Not striated- Skeletal Muscleo Development Develops from myoblast Differentiates into myotubes Myotubes fuse/link together, causing the multiple nuclei Satellite cells= stem cells, don’t become myotubes Muscle cell= muscle fibero Organization Muscles connected to bone by tendons Epimysium= outer covering of entire muscle fiber group Endomysium= outer covering around individual muscle fibers- Has a lamina See figure 10.5 in the book Sarcomere= repeating structural units of skeletal muscle fibers, segment between two z disks- Causes the appearance of striations- Myofibrils contain sarcomeres- Myosin filament reflects the A band (darker band)- Actin filament reflects the I band (lighter band)o Titin protein= coil, to allow sarcomere to spring back- H zone= unoverlapped myosin- M line= down middle, links myosin- Z disk= links actin Microfilaments—myosin and actin- Myosin= thick filament, two heavy chains (wound into helices) and4 light chains (small heads, binding sites for actin and ATP)- Actin= thin filament, globular actin and folded into helixo Tropomyosin= regulatory protein sitting in F actin, grove between helices to block myosin binding siteo Troponin= binds calcium and tropomyosin Sarcoplasmic reticulum- Smooth endoplasmic reticulum of muscle fiber- Calcium storage- Plasma membrane surrounding each muscle fiber= t tubuleo Invaginate muscle fibero Sarcomere is dialated, very dense, in these areaso Sarcoplasmic reticulum triad where interacts with t-tubule Neuromuscular junction- Somatic motor neuron junction to sarcolemma of muscle fibero At these junctions, muscle fiber is organized into hills and valleys to increase surface area- Nerve bundle branches extensively at the muscle fibero One nerve fiber can thus contact many muscle fibers- Neurotransmitter, acetylcholine, is releasedo Binds to sarcolemma receptors and changes the membrane potential in the muscle fiber DepolarizesAction potential calcium is released and begins actin/myosin interaction- Calcium binds to troponin to release tropomyosin- Heads of myosin can then bind with actincontraction ATP binds to myosin head to release actin- Rigor mortis—after death we have Calcium but no ATP so muscles remain stiff- Know MA Fast, slow, and intermediate muscle fibers- Different speeds of hydrolysis of ATP- Fast= very glycolytic, fast ATP cycling, fatigueable- Slow= lots of myoglobin, aerobic, high blood supply, can sustain, oxidative- Cardiac muscleo Anatomy Intercalated disks= desmosomes (adhering) and gap junctions (rapid ionic (Na+) changes with generation of action potential) All cells contract almost simultaneously No neuromuscular junctions No satellite cells—does not regenerate very wello micrographs the lengthy, zig-zagged lines represent intercalated disks loose sarcomere cells in the right atrium (bottom right picture)- non contractile- secrete atrial naturetic hormone—eliminates excess fluid- Smooth muscleo Anatomy Organized into strands/sheets Line blood vessels, digestive tract, etc. Most is organized into loose fascicles Endomysium-- reticular fibers surrounding (argyophillic) Dense bodies= attachment site for actin and desmin, myosin links loosely to actin- Anchors cell to cytoskeleton Many different planes of
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