BIOL 2457 1st Edition Lecture 20Outline of Last Lecture Muscle tissues Outline of Current LectureMuscle tissues Curare A plant poison used by South American Indians on arrows and blowgun darts Causes muscle paralysis by blocking ACh receptors inhibiting Na+ ion channels Derivatives of curare are used during surgery to relax skeletal muscles Anticholinesterase Slow actions of acetylcholinesterase and removal of ACh Can strengthen weak muscle contractions Ex: Neostigmine Treatment for myasthenia gravis Antidote for curare poisoning Terminates the effects of curare after surgery Production of ATP in Muscle Fibers A huge amount of ATP is needed to: Power the contraction cycle Pump Ca2+ into the SR The ATP inside muscle fibers will power contraction for only a few seconds ATP must be produced by the muscle fiber after reserves are used up Muscle fibers have three ways to produce ATP From creatine phosphate By anaerobic cellular respiration By aerobic cellular respiration Creatine Phosphate Excess ATP is used to synthesize creatine phosphate Energy-rich molecule Creatine phosphate transfers its high energy phosphate group to ADP regenerating new ATP Creatine phosphate and ATP provide enough energy for contraction for about 15 seconds Anaerobic Respiration Series of ATP producing reactions that do not require oxygen Glucose is used to generate ATP when the supply of creatine phosphate is depleted Glucose is derived from the blood and from glycogen stored in muscle fibers Glycolysis breaks down glucose into molecules of pyruvic acid and produces two molecules of ATP If sufficient oxygen is present, pyruvic acid formed by glycolysis entersaerobic respiration pathways producing a large amount of ATP If oxygen levels are low, anaerobic reactions convert pyruvic acid to lactic acid which is carried away by the blood Anaerobic respiration can provide enough energy for about 30 to 40 seconds of muscle activity Aerobic Respiration Activity that lasts longer than half a minute depends on aerobic respiration Pyruvic acid entering the mitochondria is completely oxidized generating ATP Carbon dioxide Water Heat Each molecule of glucose yields about 36 molecules of ATP Muscle tissue has two sources of oxygen Oxygen from hemoglobin in the blood Oxygen released by myoglobin in the muscle cell Myoglobin and hemoglobin are oxygen-binding proteins Aerobic respiration supplies ATP for prolonged activity Aerobic respiration provides more than 90% of the needed ATP in activities lasting more than 10 minutes Muscle Fatigue Inability of muscle to maintain force of contraction after prolonged activity Factors that contribute to muscle fatigue Inadequate release of calcium ions from the SR Depletion of creatine phosphate Insufficient oxygen Depletion of glycogen and other nutrients Buildup of lactic acid and ADP Failure of the motor neuron to release enough acetylcholine Oxygen Consumption After Exercise After exercise, heavy breathing continues and oxygen consumption remains above the resting level Oxygen debt The added oxygen that is taken into the body after exercise This added oxygen is used to restore muscle cells to the resting level in three ways Converts lactic acid into glycogen Synthesizes creatine phosphate and ATP Replaces the oxygen removed from myoglobin The tension or force of muscle cell contraction varies Maximum tension (force) is dependent on The rate at which nerve impulses arrive The amount of stretch before contraction The nutrient and oxygen availabilityThe size of the motor
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