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 I Band lighter less dense area that contains thin filaments A Band dark middle part of sacromere extends the entire length of thick filament 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 shortens Anatomy 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 each muscle 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 energized 2 Myosin heads bind to actin forming cross bridges 3 Myosin cross bridges rotate toward center of sarcomere power stroke 4 As myosin heads bind ATP the cross bridges detach from actin Contraction 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 fibers Slow type I Fast type IIa 21 40 type IIx 41 60 type IIb 61 80 1 Three Types of Skeletal Fibers associated with motor units Speed of Contraction Myosin ATPase activity ATP synthesis Rate of Fatigue Fiber Diameter Activities Slow Oxidative Slow Slow Aerobic Slow fatigue resistant Small Endurance Fast Oxidative Fast Fast Aerobic Intermediate Intermediate Sprinting walking sustained locomotion Fast Glycolytic Fast Fast Glycolytic Fast fatiguable Large Burst 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 heat Characteristics 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 Contractility Muscle Contraction 1 As nerve impulse arrives at axon terminal of a motor neuron voltage gated calcium channels open allowing calcium to enter 2 Entering calcium stimulates synaptic vesicles to undergo exocytosis releasing ACh 3 ACh diffuses across neuromuscular junction to the motor end plate on myofiber binds to receptors triggers action potential 4 Action potential travels along T tubule opening calcium channels in the SR allowing 5 Calcium ions bind to troponin on thin filament exposing binding sites for myosin calcium ions into sarcoplasm tropomyosin moves 6 Myosin heads bind to sites forming cross bridges contraction cycle begins Steps 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 are discontinuous 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 2 7 Contraction power strokes use ATP myosin heads bind to actin swivel and release thin filaments are pulled toward center of sacromere Contraction 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 Multipennate Objective 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 chest Second Class Lever designed for force effort applied at end opposite fulcrum and load in the middle ex wheelbarrow up on toes o Fulcrum in middle o 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 curl o Effort in middle Bone is lever joint is fulcrum effort is insertion point Power Point 2 Spinal Cord and ANS Objective 1 Be able to draw and label the diagram of the entire CNS
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