Lecture 4 Notes, muscular system
Lecture 4 Notes, muscular system PHYS 205
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This 7 page Class Notes was uploaded by Samantha Decker on Monday September 28, 2015. The Class Notes belongs to PHYS 205 at Ball State University taught by in Summer 2015. Since its upload, it has received 28 views. For similar materials see Fundamentals of Human Physiology in Physiology at Ball State University.
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Date Created: 09/28/15
Learning objectives I Outline the makeup of a skeletal muscle ll List the steps for the molecular basis of muscle contraction lll Understand the basic mechanistic and function of skeletal muscle lV Compare the different pathways for ATP formation in a skeletal muscle and how these relate to fatigue V Compare the characteristics of smooth or cardiac muscle tissue to skeletal muscle tissue Three Types of Muscle Tissue 1 Skeletal muscle tissue 0 Attached to bones and skin 0 Striated 0 Voluntary 2 Cardiac muscle tissue 0 Only in the heart 0 Striated O Involuntary 3 Smooth muscle tissue 0 In the walls of hollow organs eg stomach urinary bladder and airways 0 Not striated O Involuntary Special Characteristics of Muscle Tissue Excitability responsiveness or irritability ability to receive and respond to stimuli Contractility ability to shorten when stimulated Extensibility ability to be stretched Elasticity ability to recoil to resting length Functions of Skeletal Muscle Tissue Six Functions of Skeletal Muscle Tissue 1 Produce skeletal movement amp assist in uid movement Maintain posture and body position Support soft tissues Guard entrances and exits P PWF Maintain body temperature generate heat 1 Store nutrient reser glucose Muscle is structurally made up of myo brils Densely packed rodlike protein elements 80 of cell volume Sarcomere Smallest component functional unit of a muscle ber The region of a myo bril between two successive Z discs Composed of thick and thin myo laments made of contractile proteins Actin Primary structural component of thin laments Thin lament also has 2 other proteins Tropomyosin regulatory Troponin protein Each actin molecule has special binding site for attachment with myosin cross b dge Binding results in contraction of muscle ber Structure of Skeletal Muscle Titin Giant highly elastic protein largest in body 2 important roles Helps stabilize position of thick laments in relation to thin laments Greatly augments muscle s elasticity by acting like a spring Sarcoplasmic Reticulum SR 0 Network of smooth endoplasmic reticulum surrounding each myo bril 0 Functions in the regulation of intracellular CAquot2 levels T Tubules Continuous with the sarcolemma Penetrate the cell39s interior and allow the muscle to contract when stimulated Contraction The generation of force Does not necessarily cause shortening of the ber Requirements for Skeletal Muscle Contraction 1 Activation neural stimulation at a neuromuscularjunction 2 Excitationcontraction coupling Generation and propagation of an action potential along the sarcolemma Final trigger a brief rise in intracellular Caquot2 levels NeuromuscularJunction 1 Axon terminal of motor neuron forms neuromuscularjunction with a single muscle cell 2 Signals are passed between nerve terminal and muscle ber by means of neurotransmitter ACh 3 Released ACh binds to receptor sites on motor end plate of muscle cell membrane Triggers opening of speci c channels in motor end plate 1 Ion movements depolarize motor end plate producing endplate potential 2 Local current ow brings adjacent areas to threshold 3 Action potential is initiated and propagated throughout muscle ber Events in Generation of an Action Potential Local depolarization wave continues to spread changing the permeability of the sarcolemma Voltageregulated Na channels open in the adjacent patch causing it to depolarize to threshold ExcitationContraction EC Coupling 0 Sequence of events by which transmission of an AP along the sarcolemma leads to sliding of the myo laments Muscle contraction 0 AP is propagated along sarcomere to TTubules O Voltagesensitive proteins stimulate Ca2 release from SR O Ca2 is necessary for contraction Cross Bridge Cycle Continues as long as the Ca2 signal and adequate ATP are present Cross bridge formation highenergy myosin head attaches to thin lament Working power stroke myosin head pivots and pulls thin lament toward M line Cross bridge detachment ATP attaches to myosin head and the cross bridge detaches quotCockingquot of the myosin head energy from hydrolysis of ATP cocks the myosin head into the highenergy state Relaxation Depends on reuptake of Ca2 into sarcoplasmic reticulum SR Acetylcholinesterase breaks down ACh at neuromuscular junction Muscle ber action potential stops When local action potential is no longer present Ca2 moves back into sarcoplasmic reticulum Contraction Duration Depends on Duration of neural stimulus Number of free calcium ions in sarcoplasm Availability of ATP Rigor Mortis A xed muscular contraction after death Caused when lon pumps cease to function ran out of ATP Calcium builds up in the sarcoplasm AllOr None Principle Allornone principle A muscle ber either contracts completely or does not contract at all When a motor unit is stimulated all its bers contract at the same time The total force exerted by the muscle depends on the number of activated motor units Motor Units The total force exerted by the muscle depends on the number of activated motor units Motor Units Graded Muscle Responses Variations in the degree of muscle contraction Required for proper control of skeletal movement Responses are graded by 1 Changing the frequency of stumulation 2 Changing the strength of the stimulus A single stimulus results in a single contractile response a muscle twitch lsotonic Contractions Muscle changes in length and moves the load lsotonic contractions are either concentric or eccentric Concentric contractions the muscle shortens and does work Eccentric contractions the muscle contracts as it lengthens Isometric Contractions The load is greater than the tension the muscle is able to develop Tension increases to the muscle39s capacity but the muscle neither shortens or lengthens Muscle Metabolism Energy for Contraction 0 ATP is the only source used directly for contractile activities 0 Available stores of ATP are depleted in 46 seconds 0 ATP is regenerated by 0 Direct phosphorylation of ADP by creatine phosphate CP 0 Anaerobic pathway glycolysis O Aerobic respiration Aerobic Pathway Produces 95 of ATP during rest and light to moderate exercise Fuels stored glycogen then bloodborne glucose pyruvic acid from glycolysis and free fatty acids Ionic imbalances K Ca2 Pi interfere with EC coupling Prolonged exercise damages the SR and interferes with Ca2 regulation and release Total lack of ATP occurs rarely during states of continuous contraction and causes contractures continuous contractions Muscle Fiber Type Classi ed according to two characteristics 1 Speed of contraction slow or fast according to Speed at which myosin ATPases split ATP Pattern of electrical activity of the motor neurons 2 Metabolic pathways for ATP synthesis Oxidative bers use aerobic pathways Glycolytic bers use anaerobic gycoysis Muscle Fiber Type Three types Sow oxidative bers good blood supply Fast oxidative bers Fast gycoytic bers poor blood supply Smooth Muscle Found in walls of most hollow organs except heart Usually in two layers longitudinal and circular Smooth Muscle Contraction Contraction of Smooth Muscle Slow synchronized contractions Cells are electrically coupled by gap junctions Some cells are selfexcitatory depolarize without external stimuli act as pacemakers for sheets of muscle Rate and intensity of contraction may be modi ed by neural and chemical stimuli LaCkS troponin has Troponin and Calmodulin two have same camodun Cardiac Muscle Found only in walls of heart Striated Cells are interconnected by gap junctions Muscular Dystrophy Group of XIinked recessive inherited muscledestroying diseases Inability to produce dystrophin which is a structural stabilizing protein found in muscle Muscles enlarge due to fat and connective tissue deposits Muscle bers atrophy LifeSpan Changes How would a drug that blocks acetylcholine release affect muscle contraction Contraction would be prevented
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