CBIO 2200 1nd Edition Lecture 15 Outline of Last Lecture I. The RibsII. The PelvisOutline of Current Lecture I. Structure of a Muscle Fiber (Cell)II. The Skeletal Muscle FiberIII. The MyofibrilIV. SarcomereV. The Nerve-Muscle RelationshipCurrent LectureI. Structure of a Muscle Fiber (Cell)a. Elongated cellsb. Organization:i. Muscle  Fascicles  Muscle fibers (cells)  Miofibrils  Thick and thinfilaments (myofilaments)c. Mysiumi. Epimysium around muscleii. Periomysium around fasciclesiii. Endomysium around individual muscle fibers/cellsII. The skeletal muscle fibera. Multiple nucleib. Myoblasts: stem cells that fuse to make each muscle fiberc. Satellite cells: stem cells or undifferentiated myoblasts; help repopulate muscle ad. Mitochondriae. Sarcolemma: plasma membrane of musclef. Sarcoplasm: cytoplasm of muscle cellsg. Myofibrils: long protein cords that occupy the sarcoplasmh. Glycogen: storage form of glucoseThese 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.i. Myoglobin: muscle form of hemoglobin; red pigment that stores oxygen in musclej. Sarcoplasmic reticulum (SR): ER of muscles; goes around all myofibrilsk. Terminal cisternae: dilations of the sarcoplasmic reticuluml. Transverse (T) tubules: tubular infoldings which penetrate through the cell and emerge on the other sidem. Triad: composed of the two terminal cisternae and one transverse tubuleIII. The Myofibrila. Each myofibril is a bundle of parallel protein microfilaments called myofilamentsb. Thick filamenti. Myosin: shaped like a golf club, with two chains intertwined to form a shaft-like tail and a double globular head projecting from it at an angleii. Made of several hundred molecules of myosinc. Thin filamentsi. Actinii. Consists of two intertwined strands of fibrous (F) actin; each F actin is like a bead necklace1. A string of globular (G) actin makes up F actin; contain myosin binding sitesiii. Contractile proteins: do the workiv. Regulatory proteins: regulate muscle contraction1. Tropomyosin: covers myosin binding sites on actin2. Troponin: lays on top of tropomyosin; has calcium binding sites on them; when calcium binds, the troponin-tropomyosin complex roles away and reveals myosin binding sitesd. Elastic filaments: made up of springy protein called titini. Titin (aka connectin): anchors myosin to Z discs; keeps muscles from overstretchingIV. Sarcomerea. The distance between two z discsi. Anisotropic (A-band): contains thick, thin, and elastic filamentsii. H-Band: in very middle of A-band; contains thick and elastic filamentsiii. M line: in middle of H-band: complex of proteins that are there for structural purposesiv. I-band: thin and elastic filaments; go from end of A-band to the Z discb. Sarcomere shorteningi. Dystrophin and other linking proteins that transfer information to extracellular tissueii. Many different linking proteins: one of most famous is dystrophiniii. Duchenne muscular dystrophy: dystrophin linking protein is mutated in this disorderV. The Nerve – Muscle Relationshipa. Skeletal muscle will not contract without nerve signalb. Denervation atrophy: muscle atrophies when a nerve signal is blocked from the musclec. Somatic motor neurons: innervate skeletal muscles; each nerve can innervate multiple muscle fibers, but each muscle fiber is only innervated by one nerve:d. Motor unit = one nerve fiber and all the muscle fibers innervated by iti. Average motor unit: nerve innervating 200 musclesii. Large motor units: up to 1000 muscle fibers innervatediii. Small motor units: innervating 5 to 10 muscle fibers; for small motor movementse. Neuromuscular Junction: where nerve meets the musclei. It creates a distinct areaii. Synapse/neuromuscular junction: where a nerve fiber meets any muscle fiberiii. Junctional folds: in-foldings in the sarcolemma that increase surface area of ACh sensitive membranesiv. Synaptic knob: a bulbous swelling at the end of the nerve fiberv. Synaptic cleft (space between nerve and muscle )/pre-synaptic membrane (nerve membrane)/post-synaptic membrane (muscle membrane)vi. Acetylcholine receptorsvii. Schwann cell: myelin producing cellsviii.