Muscles 80197 - BIOL 2220 - 001
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80197 - BIOL 2220 - 001
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This 5 page Class Notes was uploaded by Jeni Erickson on Tuesday October 11, 2016. The Class Notes belongs to 80197 - BIOL 2220 - 001 at Clemson University taught by John R Cummings in Fall 2016. Since its upload, it has received 9 views.
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Date Created: 10/11/16
Reminders Myofibrils are within the cytoplasm and are contractile elements They are made up of individual units called sarcomeres (z- lines) Connected to the z-lines are thin myofilaments Between the myofilaments there are thick myofilaments. 200 myosin proteins are on the head of the thick myofilaments The head has two attachment sites. One for ATP that will break to release energy for the other site to open. One for thin myofilament to attach to. ATP and Calcium are crucial for contraction High energy configuration is when myofilaments are at rest. In order for muscle to relax, there must be energy. When thick and thin attach, they go from high energy configuration to low energy configuration and is making the sarcomere contract together. When ATP binds, we go back to rest Muscle will not contract unless stimulated. Nerve impulse comes to a muscle fiber, then calcium is released and muscle will contract. I neuron will only connect to a muscle cell once. There are not multiple muscle-neuron connection sites. Muscles 1. Neuromuscular junction a. Somatic motor neuron, which synapses with a skeletal muscle fiber. b. There are synaptic vesicles at the end of the neurons that carry neurotransmitters. They are released through exocytosis. c. Functional folds increase surface area so that this “connection” is more efficient. d. Acetyl Choline changes the permeability of the plasma membrane and starts the contraction e. Acetyl cholinesterase breaks down the above one so that the muscle will relax. 2. How a resting muscle gets activated to contract a. We have to stimulate it with a nervous impulse from the neuron to the muscle. (Excitation) i. Acetylcholine will trigger an action potential across sarcolemma and down T tubules. 1. The change in permeability allows sodium ions into the cell and the area depolarizes. The inside will become positive compared to the outside and that’s when we have our action potential (+30). When action potential occurs, the whole cell depolarizes. The wave of depolarization releases calcium. The influx of calcium promotes the exocytosis of Acetyl Choline. 2. T tubulus is spread to the ii. Action potential passes triads. iii. (inside of cell is -70milivolts because it has more potassium and less sodium inside the cell compared to outside) b. Sarcoplasmic Reticulum i. The muscle stores calcium and it is stored in the sarcoplasmix reticulum. ii. Triads 1. Terminal cisternae 2. T tubules 3. When tramonin C binds to calcium it causes troponin I to bind to actin. 4. ACh triggers generation of action potential across sarcolemma and down T tubules 5. Action potential passes triads 6. Terminal cisternae release calcium into sarcoplasm 7. Some calcium binds to troponin (TnC) 8. Removes tropomyosin from active sites on actin 9. Power Stroke a. Thick and thin myofilaments bound through cross bridge b. Myosin head changes from high energy to low energy configuration i. Moves toward the M line c. Pulls thin myofilament toward H zone d. ATP binds with myosin head e. Myosin and actin separate because ATP is bound to it. f. ATPase splits ATP and released energy returns myosin head to high energy position g. Cycle repeats as long as calcium and ATP are present h. This power stroke can occur about 5 times a second and there are about 200 myosin proteins present. i. The contraction is an all or none phenomenon. It will shorten or lengthen to the same point every time (to its greatest ability). j. The way we get a stronger muscle contraction is to stimulate more muscle fibers together. 10. Recovery a. Calcium actively pumped back into sarcoplasmic reticulum b. Reduced calcium frees tropomyosin to block actin active sites c. Cross bridge disconnects because energy has made it let go. d. Muscle relaxes 11. Motor Unit a. One motor neuron can attach to multiple muscle fibers, but one muscle fiber does not attach to multiple motor neurons. b. Combination of motor neuron and all the fibers it stimulates c. Not all motor units in a muscle fire at the same time i. We alternate which motor units are used, we can strengthen contraction and prevent fatigue. 12. Types of Contraction a. Twitch: a single stimulus causing a single contraction. i. Latent period: Period of time between when the stimulus occurs and the muscle contracts. ii. Contraction phase: calcium is available , etc., power stroke 1. If we stimulate the muscle again during the contraction phase, nothing will happen because it is already contracting. 2. Refractory period: where another stimulation will not cause another contraction. iii. Relaxation phase. b. Tetanus: When a second contraction before there was a complete relaxation. The frequency of stimulation must be greater than the refractory period. The strength of the contraction gets stronger. i. Incomplete: muscle begins to relax (partial, not total) ii. Complete: no relaxation of the muscle at all. The muscle is stimulated at the peak for the contraction phase. iii. Wave summation: when second stim is applied before complete relaxation. It goes to a certain maximum. c. Treppe: the repeated use of a muscle even with relaxation will allow the contraction strength to get stronger. (warm- up in exercise makes muscles more efficient for competition) d. Isotonic: muscle will change length and move a load. Movement occurs. e. Isometric exercise: there is no movment and the muscle does not change length. The load is greater than the power of a muscle. (trying to lift something that is was too heavy ) 13. Energy for contraction a. Direct phosphorylation: muscle stores creatine phosphate. i. Creatine phosphate couples with ADP to produce ATP ii. Can power muscle for up to 15 seconds iii. CP reserves replenished during periods of inactivity iv. Creatine comes from our diet 1. Enzyme Creatinephosphate kinase b. Anaerobic respiration: i. Glycolysis breaks down glucose. ii. Glucose comes from blood stream (blood glucose) and what is stored in the muscle(glycogen) iii. Pyruvic acid converted to lactic acid iv. Lactic acid diffuses into bloodstream. changes pH in the muscle and stops muscle contraction. v. Liver takes lactic acid and converts it back to pyruvic acid to make new glucose. (recycles it) vi. Net gaine of 2 ATP molecules. Produces it quickely. vii. Will power us for a minute. c. Aerobic respiration: slowest pathway of energy production. i. Glycolysis breaks down glucose ii. Pyruvic acid enters mitochondria for complete breakdown 14. Muscle Fatigue a. Stops energy production. b. ATP use exceeds ATP production c. Excessive accumulation of lactic acid d. Ionic imbalances i. Especially potassium e. We still get stimuli for the muscle to contract, but the muscle cant do it. You could get cramping.
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