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A&PII Objectives Power Point #1: Muscular System and Review Objective 1. Define and identify the anatomy of skeletal muscle and explain the sliding filament theory leading to muscle contraction. General Anatomy of Skeletal Muscle:Skeletal muscle consists bundles of muscle cells called fascicles. Muscle cells, also called myofibers are composed of myofibrils, which contain the smallest contractile units, known as sacromeres. Sacromeres are made up of myofilaments, which contain the contractile proteins actin (thin) and myosin (thick). - A-Band: dark middle part of sacromere, extends the entire length of thick filament- I-Band: lighter, less dense area that contains thin filaments- H-zone: bisected by M-line, where no thick and thin filament overlap- M-line: composed of proteins that keep the sacromere in proper spatial orientation as it lengthens and shortensAnatomy of Skeletal Muscle Fiber:A muscle fiber consists of multiple nuclei (myonucleated) located just beneath the sacrolemma, the plasma membrane of a muscle cell. These cells are terminally differentiated meaning there are a set number of cells when born. Muscle growth arises from hypertrophy, increase in size of muscle cell, as opposed to hyperplasia, and increase in number of muscle cells. Transverse tubules tunnel in from surface toward center of eachmuscle fiber, increasing conduction of action potentials. The sacroplasmic reticulum surrounds each myofibril, serving as a storage site for calcium. Release of calcium from SR triggers muscle contraction.Sliding-Filament Theory:Skeletal muscle shortens during contraction because thick and thin filaments slide past one another by way of the Sliding-Filament Mechanism. When the sacroplasmic reticulum releases calcium into the sarcoplasm, where it binds to troponin (regulatory protein). Tropomyosin (regulatory protein) moves away from myosin-binding site on the actin filament, allowing the Contraction Cycle to begin. 1. Myosin heads hydrolyze ATP-now reoriented and energized2. Myosin heads bind to actin, forming cross-bridges3. Myosin cross-bridges rotate toward center of sarcomere (power stroke)4. As myosin heads bind ATP, the cross-bridges detach from actinContraction cycle continues if ATP is available and calcium in sacroplasm is high.Objective 2. Define and distinguish between the types of muscle fibers and explain the possibilities (or lack there of) of fiber type morphology. Myosin heavy chain (MHC): Isoforms (fiber types based on speed of conduction due to enzyme)- Speed determined by increasing ATPase activity in myosin head; these isoforms provide different energy transduction kinetics and crossbridge turnover rates during contraction- Training increases Type IIa fibers, while decreasing Type IIx fibersSlow: type IFast: type IIa (21-40), type IIx (41-60), type IIb (61-80)1Three Types of Skeletal Fibers (associated with motor units):Slow Oxidative Fast Oxidative Fast GlycolyticSpeed of Contraction Slow Fast Fast Myosin ATPase activity Slow Fast FastATP synthesis Aerobic Aerobic GlycolyticRate of Fatigue Slow (fatigue resistant) Intermediate Fast (fatiguable)Fiber Diameter Small Intermediate LargeActivities Endurance Sprinting, walking, sustained locomotionBurst of power (ex: hitting a baseball)Objective 3. State the different types of skeletal muscle contraction and the functions and characteristics of skeletal muscle.Functions of Skeletal Muscle: Produce movement, maintain posture, stabilize joints, and generate heatCharacteristics of Skeletal Muscle:- Excitability: nerve must innervate and excite the muscle, causing muscle contractions; ability to respond to certain stimuli by producing electrical signals called action potentials- Extensibility: ability of muscular tissue to stretch, within limits, without being damages - Elasticity: ability of muscular tissue to return to its original length and shape after contraction or extension-ContractilityMuscle Contraction:1. As nerve impulse arrives at axon terminal of a motor neuron, voltage-gated calcium channels open allowing calcium to enter2. Entering calcium stimulates synaptic vesicles to undergo exocytosis, releasing ACh3. ACh diffuses across neuromuscular junction to the motor end plate (on myofiber), binds to receptors, triggers action potential4. Action potential travels along T-tubule opening calcium channels in the SR, allowing calcium ions into sarcoplasm5. Calcium ions bind to troponin on thin filament, exposing binding sites for myosin (tropomyosin moves)6. Myosin heads bind to sites forming cross-bridges contraction cycle beginsSteps 3-6 represent Excitation-Contraction Coupling: the steps that connect excitation to contraction (sliding of filaments)- Coordinated-Coupled Gating Mechanism: regions between T-tubule and SR arediscontinuous, consisting of discrete RyR1 channel subunits,o Mechanism may allow concerted activation of RyR1 calcium release channels during EC-coupling of skeletal muscle by triggering one RyR1 cannel that may activate all associated RyR1 channels in that junction.27. Contraction: power strokes use ATP; myosin heads bind to actin, swivel, and release; thin filaments are pulled toward center of sacromereContraction cycle (sliding-filament mechanism) continues if ATP is available and calcium levels in sarcoplasm are high.Objective 4. What are the different types of fascicle arrangements? Also, what determines a muscles power and ROM? Fascicle Arrangements: determines a muscle’s power and Range of Motion (greatest number of fibers has the most power)- Circular: arranged in rings- Fusiform: spindle-shaped- Parallel: run parallel along axis, ex: Sartorius- Convergent: broad origin and fascicles move toward insertion, ex: Pectorialis Major- Pennate: attach obliquely to a central tendon, “featherlike”o Unipennate, Bipennate, MultipennateObjective 5. Describe the 3 classes of levers and apply the knowledge to uses of mechanical advantage and muscle insertions to determine lever classes in the body. - First-Class Lever: designed for balanced movements; effort and load are on ends and fulcrum is in middle; ex: scissors, lifting head off chesto Fulcrum in middle- Second-Class Lever: designed for force; effort applied at end opposite fulcrum and load in the middle; ex: wheelbarrow, up on toeso Load in middle- Third-Class Lever: designed for speed and range of motion (most common); effort is between the load and fulcrum, always a mechanical disadvantage; ex: bicep curlo


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FSU PET 3323C - Notes

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