BIOL 243 3rd Edition Lecture 1 (March 18)I. Muscle Contractiona. the shortening of distance between Z lines due to sliding filament; filament does not shorten; I bands get shorterb. Calciumi. Release stimulates contraction; stored in the SRii. Absence of calcium causes tropomosyin to block interactioniii. Presence of calcium, calcium binds with troponin C to remove the tropomyosin blockc. Steps of Contraction (can be cyclic)i. Cross Bridge Formation-Actin binds to myosin (ADP and Pi)ii. Power Stroke (working stroke)-myosin head changes structure. ADP and Pi are released.iii. Detachment as ATP bindsiv. Cocking –return of myosin to original structure (reset); ATP hydrolysis back to ADP and Pid. Rigor Mortis-muscle stiffness that occurs after death; cells cannot exclude or control calcium. There is also not ATP so detachment does not occure. Regulation of contractioni. Motor neuron-end is called axon terminalii. Neuromuscular juncture-where neuron communicates with the muscleiii. NMJ and axon terminal do not touch-synaptic cleftiv. NT in skeletal muscle-acetylcholine (Ach)-released by exocytosis1. Signal reaches axon terminal2. ACh is released3. ACh diffuses across the synaptic cleft4. ACh binds to a receptor (signal on sarcolemma-plasma membrane)5. Signal will travel down into the T tubules (continuation of the sarcolemma p.m.)6. Stimulates the release of calcium → muscle contractionv. Turn off/Relax1. Ways to remove ACh from the synaptic clefta. Acetylcholinesterase-breaks down AChb. ACh diffuses awayc. ACh taken up by neurons to be reused2. Calcium is pumped back into the sarcoplasmic reticulumf. Myogram-graphed plot of a twitch (tension vs time)i. Latent period (little tension)ii. Period of contraction (tension increases)iii. Period of relaxtion (decreasing tension)Lecture 2 (March 20)g. How to achieve Smooth Contractionsi. Increase the frequency of stimulation1. wave summation-apply another stimulus to muscle before it relaxes completely2. fused tetanus-no relaxation at all between stimuliii. Multiple motor unit summation1. Motor unit-one motor neuron and the fibers it supplies2. 4-200 fibers per motor unit3. Fibers of the motor unit are not clustered together4. Many motor units in a muscle5. All muscle fibers of a motor unit with have the same fiber type6. Nerve modifies the muscle into fiber type7. Process: two motor units are stimulated. The 2nd is stimulated out of phase. The result is a net smooth contractioniii. Other definitions1. Treppe-warm up2. Isotonic-muscles shorten and move a load. Ex: lifting a pencil3. Isometric-muscles develop tension but do not move a load because the load is greater than the tension muscles can create. Ex pushing a wallh. Factors affecting the force generated by musclesi. Number of fibers contracting/number of motor units activatedii. Frequency of stimulationiii. Size of a muscleiv. Stretch-sacromeres have an optimal stretch range of 100-120%i. Energyi. Muscles use ATP, which is hydrolyzed into ADP and Piii. Sources of Energy1. ATP soluble in cells (lasts 6 seconds) 2. Direct phosphorylation: Creatine phosphate-high energy bond; CP+ADP→(creatine kinase)→creatine+ATP; lasts for 10-15 seconds3. Aerobic respiration-uses glucose; requires oxygena. Glucose + oxygen →carbon dioxide + water + energyb. Energy produced used to phosphorylate ADP into ATP4. Breakdown of Glucose and Oxygen (aerobic respiration)a. Glycolysis (6C) → pyruvic acid (3C) ADP phosphorylated into ATP; occurs in the cytoplasmb. Oxidative Phosphorylationi. Continuation from pyruvic acid; Creates 20 times more ATP than glycolysisii. Occurs in the mitochondria iii. Gives off carbon dioxide and water5. Anaerobic Respiration-pyruvic acid is converted into lactic acid; works fast; creates burn in musclesj. Oxygen Debt-when we use more ATP than the ATP generated in the aerobic pathwayi. Muscle fatigue1. Due to lack of ATP-cocking can’t occur (cramps)2. Deficiency in potassium or sodium3. Accumulation of lactic acidk. Fiber types-all skeletal but have different characteristicsi. Slow Oxidative1. Fatigue resistant2. Small3. Slow myosin with long period of contraction4. Relatively high levels of myoglobin that bind to and store oxygen5. Have lots of mitochondria-specialized for aerobic respiration6. Good for long distance runnersii. Fast Oxidative1. Fatigue resistant2. Intermediate3. Fast myosin4. Reasonable amount of myoglobin5. Specialized for aerobic respiration6. Lots of mitochondriaiii. Fast Glycolytic1. Fatigable2. Tire easily3. Fast myosin with short time of contraction4. Little or no myoglobin5. High levels of glycolytic enzyme6. Strong, broad fibers7. Good for sprintersII. Terminiologya. Flaccid-less than normal muscle tone; usually due to nervous stimulation problemb. Atrophy-wasting of musclec. Hypotrophy-muscle enlargementd. Muscular dystrophies-muscle destroying diseases; genetic and more prevalent in males; X linkedIII. Development and regeneration; Characteristicsa. Skeletal musclei. Single cells divide, fuse, then form multi nucleated muscle cellsii. Adults have some residual cells called satellites or myoblastsiii. Upon injury satellite cells will divide and eventually fuse to form more skeletal muscleiv. Limited capacity b. Cardiac musclei. Does not regenerateii. If injured will convert to connective tissue and fatc. Smooth musclei. Not striated; involuntaryii. No t tubulesiii. Have thick and thin filaments but in a different ratio (1:2 in skeletal, 1:10-13 in smooth)iv. No troponin v. No sarcomerevi. Will contain bundles of thin filaments and intermediate filaments that attach to dense bodiesvii. No z discsviii. Lack elaborate coveringix. 2 sheets of muscle cells1. circular2. longitudinalx. lack structured neuromuscular junctions (diffuse junction)xi. wide synaptic cleftxii. many nerve endingsIV. Contraction of smooth musclea. Low, synchronized b. Electrically coupledc. Regulated by calciumd. Different pathwaye. Latent period is 20-50 times longer than skeletalf. Can maintain contraction using 1% of the energy used by skeletal muscleg. Regulation of contractioni. Nervous-using neurotransmitters ACh and norepinephrineii. Non nervous-pacemakerh. Typesi. Single unit-contract as sheet, electrically coupled by gap junctionii. Multi unit-percisely controlled; very few gap junctions; ex arrector piliV. The Nervous Systema. Fast actingb. Sensory input, integration, motor outputc. Effector-musclesd. Regulate the release of various substances from