Muscle Physiology Review PDF

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Lecture Notes Week 14...

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Muscle Physiology Review A Learning Objectives 1 Describe the organization and structure of a skeletal muscle, including the arrangement of Actin and Myosin microfilaments within a sarcomere. 2 Draw a diagram of the T-tubules and the sarcoplasmic reticulum that coordinate Calcium release within the muscle contraction 3 Explain the four steps of the Myosin activity cycle 4 Compare intraneuronal synapses and the synapses between motor neurons and muscle called neuromuscular junctions (NMJs) 5 Describe the different types of muscle contractions and the mechanics of a single-fiber contraction B Describe the organization and structure of a skeletal muscle, including the arrangement of Actin and Myosin microfilaments within a sarcomere. 1 Three Types of Muscle Fibers a Skeletal muscle; cardiac muscle; smooth muscle b Skeletal Muscle i Muscle  Group of muscle cells bound together by connective tissue  Function to move the skeleton via tendon connections

ii Extremely large cells  Called fibers iii Multinucleated  Fusion of many undifferentiated mononucleated myoblasts  Each nucleus regulates local domain  Satellite cells differentiated into myoblasts to repair or replace damaged fibers 2 Sarcomere – contractile unit within a muscle fiber a Myofibril i Cylindrical bundle of thick (myosin) and thin (actin) filaments 3 Muscle Contraction a NMJ i Specialized chemical synapse ii Ach at nicotinic receptors b Motor end plate potential i AP from motor efferent contracts muscle ii mEPP is specialized EPSP iii ALWAYS excitatory c Junctional folds i High expression of nAchR

ii Decrease diffusion of Ach iii Clearance via AChE C Explain the four steps of the Myosin activity cycle 1 Myosin Activity Cycle a Binding to ATP, ADP + Pi, or ADP yields different conformations i Cross bridge formation (ADP + Pi & circle straight aligned touching the top) ii Power stroke (ADP + Pi leaves & line is raised and circle is tilted) iii Cross bride detachment (+ATP & line is low and circle is tilted) iv Reactivation of myosin (ADP + Pi & line is low and circle is straight) D Describe the different types of muscle contractions and the mechanics of a single-fiber contraction 1 Somatic Motor System a Voluntary control of movement i Muscles are organized into groups and work with the skeleton to perform specific actions  Flexor  Extensor  Synergist  Antagonist 2 Types of contractions

a Muscle fiber contraction does not necessarily change length of the muscle i May shorten, lengthen or no change ii Determined by the magnitude of load on the muscle b ISOTONIC i Muscle changes length while the load on muscle remains constant ii Concentric or eccentric c ISOMETRIC i Muscle supports a load in constant position 3 Mechanics of Single-Fiber Contractions a Twitch contraction i Mechanical response to a single action potentials  Latent period & contraction time ii Differ with isometric & isotonic movements within same fiber b Load-velocity relation i Light objects can be moved faster  Shortening velocity is greatest when there is no load ii Hyperbolic response  Lengthening velocity increases with loads greater than isometric tension c Frequency-tension relation

i Summation of muscle tension from successive action potentials ii Tetanus is a maintained contraction in response to repetitive stimulation  Fused or unfused  Persistent elevation of cytosolic calcium d Length-tension relation i Titin filaments anchor & align thick filaments and connect M line proteins to the Z disk  Responsible for elastic properties of relaxed muscles (passive)  Limits the range of motion of the sarcomere ii Optimal length of the muscle will generate the most isometric tension (active)  Passive elastic forces keep the muscle near this length at rest...