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A&P Lec Chap 11 Pt2
A&P Lecture Chap 11 A&P Lecture WK 5 Chap 11 Muscular Tissue Pt2
| Term | Definition |
|---|---|
| Easier to remember excitation/contraction steps - an individual twitch (excitement part) | 1. Signal from motor neuron causes plasma membrane to depolarize 2.Signal travels across membrane, down T-tubules |
| Easier to remember excitation/contraction steps : (Managing regulatory proteins) | 3. Sarcoplasmic reticulum releases calcium (Ca2+) 4. Calcium (Ca2+) binds to troponin (regulatory protein that regulates actin and myosin being together=a contraction) 5. Releases tropomyosin and it uncovers actin |
| Easier to remember excitation/contraction steps : (Contraction) | 6. Myosin binds to actin and pulls it toward the center/M-line |
| Muscle twitch: | quick cycle of contraction and relaxation when a muscle is directly stimulated with an electrode |
| Muscle twitch can change by higher voltage: | stronger contraction or lower voltage: weaker contraction |
| Muscle twitch can change by higher frequency: | speed of contractions |
| Muscles must contract with variable strength for different tasks Stimulating the nerve with higher voltages produces stronger contractions: | - Higher voltages excite more nerve fibers which stimulate more motor units to contract - Recruitment or multiple motor unit (MMU) summation: - Occurs according to the size principle: |
| Recruitment or multiple motor unit (MMU) summation: | the process of bringing more motor units into play with stronger stimuli |
| size principle: | weak stimuli (low voltage) recruit small units, while strong stimuli recruit small and large units for powerful movements |
| Frequency of stimulation also affects twitch strength: | can cause twitch vs. tetany |
| Low frequency stimuli produce | identical twitches |
| Higher frequency stimuli produce | temporal (wave) summation - Each new twitch ‘rides piggyback” on the previous one, generating higher tension - Only martial relaxation between stimuli resulting in fluttering incomplete tetanus |
| Unnaturally high stimulation frequencies (in lab experiments) cause a | steady, contraction called complete (fused) tetanus - only if you have the electrode machine |
| Tetany in human bodies: | is incomplete tetany and complete tetany is only if you have the electrode machine for constant output of stimulus |
| Alternating motor units: | are when motor units overlap one another to make up for the relaxation period of the other - makes for constant sustained contraction |
| Two types of contractions: | isometric (iso/same metric/length) contraction and isotonic contraction (iso/same tension/tonic) |
| Isometric contraction: | contraction w/out a change in length - has change in tension - Posture muscles - produces internal tension but external resistance causes it to stay same length |
| Isotonic contraction: | muscle contraction with a change in length but no change in tension Has concentric vs. eccentric contraction |
| (Isotonic contraction): Concentric contraction: | shortening under tension Muscle shortens as it maintains tension (lifting weights) |
| Isotonic contraction): Eccentric contraction: | lengthening under tension (as it maintains tension) (slowly lowering weights) All muscle contractions depend on ATP to occur and relax ATP supply depends on availability of oxygen and organic energy sources (for example, glucose and fatty acids) |
| Two main pathways of ATP synthesis | : anaerobic fermentation and aerobic respiration |
| Anaerobic fermentation: | enables cells to produce ATP in absence of oxygen; yields little ATP & lactate, (needs to be disposed by liver) - NO oxygen - high intensity - Fast (30-40 seconds) - Produces some ATP - Creates lactate acid (byproduct) and causes burning |
| Aerobic respiration: | produces far more ATP; does not generate lactate; requires a continual supply of oxygen Slower (90 seconds) Produces lots of ATP and no byproduct Requires oxygen |
| Sources of energy: | Free ATP, creatine phosphate, anaerobic fermentation, aerobic respiration |
| Fast to slow sources of energy: | free ATP, creatine phosphate (only takes a couple of seconds), anaerobic fermentation (40 seconds to make ATP), and aerobic respiration (90 seconds) Not a linear pathway |
| Immediate energy (intense exercise) | Oxygen is briefly supplied by myoglobin but is rapidly depleted Muscles meet most ATP demand by borrowing phosphate groups (P1) from other molecules and transferring them to ADP |
| Two enzyme systems control these phosphate transfers: | myokinase and creatine kinase |
| Myokinase: | transfers phosphate 1 from one ADP to another, converting the latter to ATP |
| Creatine kinase | : obtains phosphate 1 from a phosphate storage molecule Creatine Phosphate CP) and gives it to ADP to become ATP |
| Phosphagen system: | the combination of ATP and CP which provides nearly all energy for short bursts of activity (ex: sprinting) |
| Short term energy: | as phosphagen system is exhausted, muscles shift to anaerobic fermentation - Muscles obtain glucose from blood & their own stored glycogen - w/no oxygen glycolysis can generate a net gain of 2 ATP - Converts glucose to lactate |
| Anaerobic threshold (lactate threshold): | point at which lactate becomes detectable in the blood |
| Glycogen–lactate system: | the pathway from glycogen to lactate Produces enough ATP for 30–40 s of maximum activity |
| Long-term energy: | After abt 40 seconds, respiratory and cardiovascular system start to deliver oxygen fast enough for aerobic respiration to meet most of muscle’s ATP demand |
| Aerobic respiration produces more ATP per glucose than | glycolysis does (another 30 ATP per glucose) |
| Efficient means of meeting the ATP demands of prolonged exercise After 3–4 min, the rate of | oxygen consumption levels off to a steady state where aerobic ATP production keeps pace with demand For 30 min energy comes equally from glucose and fatty acids Beyond 30 min, depletion of glucose causes fatty acids to become the more significant fuel |
| Muscle fatigue: | progressive weakness from prolonged use of muscles |
| Fatigue in high-intensity exercise is thought to result from: | Potassium accumulation in the T-tubules reduces excitability ADP and phosphate 1 accumulation: slows cross-bridge movements, inhibit calcium release and degreases force production in myofibrils |
| Fatigue in low-intensity (long duration) exercise is thought to result from: | - Fuel depletion as glycogen and glucose levels decline - Electrolyte loss through sweat can decrease muscle excitability - Central fatigue when less motor signals are issued from brain; brain cells inhibited by exercising muscles release of ammonia |
| Excess postexercise oxygen consumption (EPOC) or oxygen debt: | elevated rate of oxygen consumption following exercise |
| EPOC purpose: | aerobically replenish ATP (some of which helps regenerate CP stores) Replace oxygen reserves on myoglobin Provide oxygen to liver that is busy disposing of lactate Provide oxygen to many cells that have elevated metabolic rates after exercise |
| EPOC can be six times basal consumption and | last an hour (baseline) Heart has tons of myoglobin and does not produce lactate |
| Myoglobin: | pigmented protein that holds oxygen - iron-containing protein found in cardiac and skeletal muscle tissue that stores and transports oxygen |
| Oxygen debt occurs because | we have to put stuff away and get rid of byproduct |
| Skeletal muscle fibers are classified into two major physiological classes: | Slow-twitch cells and fast-twitch cells |
| Slow-twitch, slow oxidative (SO), red fibers, or type 1 fibers: | Well adapted for endurance;resist fatigue by oxidative (aerobic) ATP production - Important for muscles that maintain posture - Thin cells w abundant mitochondria, capillaries, myoglobin - myosin w slow ATPase - SR that releases calcium slowly |
| slow twitch is | Grouped in small motor units controlled by small, easily excited motor neurons allowing for precise movements |
| Slow twitch cells breakdown: | Are adapted for endurance (ex: walking) Have lots of myoglobin Is a darkish color Are posture muscles Thin cells Aerobic respiration |
| Fast twitch, fast glycolytic (FG), white fibers, or type 2 fibers: | Fibers well adapted for quick responses; utilize glycolysis and anaerobic fermentation for energy - Abundant in quick and powerful muscles; eye and hand muscles - form of myosin w fast ATPase - large SR that releases calcium quickly |
| fast twitch has | Fibers are thick and strong; low myoglobin gives them a pale color Grouped in large motor neurons allowing for powerful movements |
| An intermediate, or fast oxidative (FO) fiber type: | is known mainly in other mammals but relatively rare in humans |
| Fast twitch cells breakdown | High intensity Have burst activity Low myoglobin Increase in creatine phosphate stores Are thick cells Have powerful contractions Anaerobic fermentation |
| Every muscle contains a mix of fiber types but one type predominates depending on muscle function | Fiber type within a muscle differs across individuals Some individuals seem genetically predisposed to be sprinters, with others more suited for endurance |
| Factors that affect muscular strength: | size and arrangement |
| Muscle size: | thicker muscle forms more cross-bridges; a muscle can exert tension of 3 or 4 kg/cm^2 of cross-sectional area |
| Fascicle arrangement: | pennate are stronger than parallel, and parallel stronger than circular If a bundle is going in the same direction it is stronger than those going in different directions |
| Size of active motor units: | the larger the motor unit, the stronger the contraction |
| Cardiac and smooth muscle share certain properties: | Their cells are myocytes: not as long and fibrous as skeletal muscles - relatively short & have 1 or 2 nuclei - involuntary: not usually under conscious control - receive innervation from the autonomic nervous system (not somatic motor neurons) |
| Cardiomyocytes: | Cardiac muscle cells |
| Properties of cardiac muscle: | - Heart beats with a regular rhythm - autoregulated - Contracts without fail (whether sleep/concious) - Highly resistant to fatigue - Contractions must last long enough to expel blood - Muscle cells of a given chamber must contract in unison |
| Structure and function of cardiac muscle cells: | Striated, relatively short and thick, and surrounded by endomysium (but no peri- or epi) Cardiomyocytes branch and join to other cells at connections called intercalated discs |
| cardiac muscle cell junctions | - Electrical gap junctions allow each cardiomyocyte to directly stimulate its neighbors - Mechanical junctions that keep the cardiomyocytes from pulling apart very limited mitosis, so cardiac muscle cells repair by fibrosis |
| cardiac muscle structure/func | - Highly resistant to fatigue - Autorhythmic - After a heart attack, functional muscle is not regenerated - Can contract without need for nervous stimulation; - Stimulation from autonomic nervous system can modify contraction rate and strength |
| Heart is autorhythmic: | able to contract rhythmically and independently |
| Intercalated discs: | located at the longitudinal ends of cardiac muscle cells mechanically bind cardiac muscle cells together and electrically couples them, allowing for the rapid, synchronized spread of electrical signals needed for a coordinated heartbeat. |
| Structure and function of smooth muscle: | Does not have sarcomere arrangements - has actin and myosin that creates a net surface than being regulated for contractions is inside our hollow organs, digestive/urinary tract, blood vessels |
| smooth muscle mitosis and contraction | Stimulus is varied: not only motor neurons Contraction duration is longer but slower to contract Is able to regenerate Capable of mitosis and hyperplasia |
| Smooth muscle can contract (or relax) in response to a variety of stimuli (excitation): | Autonomic nerve fibers and neurotransmitters Chemicals: hormones, oxygen, low pH Temperature Stretch Autorythmicity |
| Name a couple of ways smooth is different from cardiac and skeletal: | Smooth has no sarcomere, different and more complex way of contraction, can regenerate if damaged, longer contraction |
| Stimulus for skeletal muscle is motor neurons | Stimulus for cardiac muscle is it is autoregulated |
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