Final Exam Study Guide Lecture 21 Structural Components of a Sarcomere Skeletal Muscle Contraction o The process of contraction Neural stimulation of sarcolemma Causes excitation contraction coupling Muscle fiber contraction Caused by thick and thin filament interactions Tension production An overview of skeletal muscle contraction picture Action potential that travels along the sarcolemma and down the T tubule cause release of Ca2 which allows for actin myosin interaction Components of the Neuromuscular Junction The Control of Skeletal Muscle Activity o The neuromuscular junction NMJ Special intercellular connection between the nervous system and skeletal muscle fiber Action potential reaches the axon terminal of motor neuron causes release of ACh into synaptic cleft ACh binds chemically gated Na channels on muscle opening them Na influx to depolarize the muscle fiber Action potentials generated in muscle fiber along inner surface of the sarcolemma Skeletal Muscle Innervation picture AChE breakdown of ACh prevents overstimulation of muscle by motor neuron Excitation Contraction Coupling o Action potential reaches a triad T tubule and terminal cisternae of the sarcoplasmic reticulum Releasing Ca2 from the terminal cisternae of the sarcoplasmic reticulum first step to excitation contraction coupling Triggering contraction IF The myosin heads are in primed high energy position Used ATP energy to get into this position ATP hydrolyzed to ADP Pi on myosin head Skeletal Muscle Contraction The Contraction Cycle KNOW THIS FOR THE EXAM 1 Contraction Cycle Begins 2 Active Site Exposure 3 Cross Bridge Formation 4 Myosin Head Pivoting 5 Cross Bridge Detachment 6 Myosin Reactivation The Contraction Cycle KNOW THESE STEPS AND WHATS GOING ON step 6 red note Fiber Shortening o As sarcomeres shorten muscle pulls together producing tension o Muscle shortening can occur at both ends of the muscle or at only one end of the muscle This depends on the way the muscle is attached at the ends Usually muscle held in position at origin with the insertion end moving towards the fixed end Skeletal Muscle Relaxation Relaxation o Contraction duration Depends on Duration of neural stimulus how much ACh is released by the motor neuron Number of free calcium ions in sarcoplasm Availability of ATP Relaxation occurs when o Ca2 concentrations fall causing Ca2 detaches from troponin Active sites are re covered by tropomyosin Rigor Mortis A fixed muscular contraction after death 2 7 hrs after death o Caused when Ion pumps cease to function ran out of ATP Calcium builds up in the sarcoplasm What causes the end of rigor mortis 1 6 days after death Skeletal Muscle Contraction and Relaxation Summary o Skeletal muscle fibers shorten as thin filaments slide between thick filaments o Free Ca2 in the sarcoplasm triggers contraction o SR releases Ca2 when a motor neuron stimulates the muscle fiber o Contraction is an active process o Relaxation and return to resting length are passive Tension Production and Contraction Types Tension Production by Muscles Fibers o As a whole a muscle fiber is either contracted or relaxed o Depends on The number of pivoting cross bridges The fiber s resting length at the time of stimulation The frequency of stimulation o Length Tension Relationships Number of pivoting cross bridges depends on Amount of overlap between thick and thin fibers Optimum overlap produces greatest amount of tension Too much or too little reduces efficiency why Normal resting sarcomere length Is 75 to 130 of optimal length o The Frequency of Stimulation A single neural stimulation produces A single contraction or twitch Which lasts about 7 100 msec Sustained muscular contractions require many repeated stimuli o Characteristics of muscle twitches 1 Latent period The action potential moves through sarcolemma Causing Ca2 release from 2 Contraction phase Calcium ions bind to Tension builds to peak 3 Relaxation phase Ca2 levels fall Active sites are covered and tension falls to resting levels o Treppe A stair step increase in twitch tension Caused by repeated stimulations immediately after relaxation phase Stimulus frequency 50 second Causes a series of contractions with increasing tension Increase in tension caused by gradual increase in Ca2 concentration in sarcoplasm Ca2 pumps not fast enough to pump released Ca2 back into SR o Wave summation Increasing tension or summation of twitches Repeated stimulations before the end of relaxation phase Stimulus frequency 50 second Causes increasing tension or summation of twitches o Incomplete tetanus If rapid stimulation continues and muscle is not allowed to relax twitches reach maximum level of tension o Complete tetanus Twitches reach maximum tension If stimulation frequency is high enough muscle never begins to relax and is in continuous contraction o Note disease tetanus lockjaw caused by toxin from Clostridium tetani bacterium that causes over activity of skeletal muscle motor neurons Results in muscle stiffness headaches difficulty swallowing o Depends on Internal tension produced by muscle fibers External tension exerted by muscle fibers on elastic extracellular fibers Total number of muscle fibers stimulated Motor Units and Tension Production Motor units in a skeletal muscle o Contain hundreds of muscle fibers contract at the same time o Controlled by a single motor neuron o Recruitment multiple motor unit summation In a whole muscle or group of muscles smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated o Maximum tension Achieved when all motor units reach tetanus Can be sustained only a very short time o Sustained tension Less than maximum tension Allows motor units rest in rotation how o Muscle tone The normal tension and firmness of a muscle at rest Muscle units actively maintain body position without motion Increasing muscle tone increases metabolic energy used even at rest o Contraction are classified based on pattern of tension production Two types 1 Isotonic contraction Skeletal muscle changes length resulting in motion If muscle tension load resistance Muscle shortens concentric contraction If muscle tension load resistance Muscle lengthens eccentric contraction 2 Isometric contraction Skeletal muscle develops tension but is prevented from changing length iso same metric measure Load and Speed of Contraction o Are inversely related o The heavier the load resistance on a muscle The longer it takes for
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