Muscular System PDF

CHAPTER 6 The Muscular System  Muscle tissue: 40% of body weight (males), 32% (females). Skeletal muscle: produces movement, generally under voluntary con...

CHAPTER 6 The Muscular System  Muscle tissue: 40% of body weight (males), 32% (females). Skeletal muscle: produces movement, generally under voluntary control Cardiac muscle: the heart Smooth muscle: involuntary. (Food through digestive tract, diameter of blood vessels, urinary bladder, uterus, etc.) Arnold: the man, the myth, the legend!  Muscle Function:Produce Movement Principle function Muscles contract: distance shortened between bones (for skeletal muscles), then relax. Skeletal muscle moves bone, attached by tendons Muscle groups Synergistic: different muscles work together for a movement (turning the head) Antagonistic: different muscles produce opposite motion (reciprocal innervation: antagonistic groups do not contract at the same time) The Muscular System: antagonistic groups a a b c b c  Origins Insertations  Muscle Structure A muscle: all cells with the same insertation and origin are part of the same muscle. Fascicles: bundles of cells, connective tissue surrounding each bundle joins, forming tendons. Myofibril bundles in each muscle cell Myofibrils with sarcomeres laid out end to end 1 sarcomere Basic muscle contractile unit: a sarcomere Skeletal muscle cells are multinucleic: they were many cells that became fused together, end to end A muscle has many fascicles, which has many cells, which have many myofibrils, which are many sarcomeres laid out end to end. Slide 6.4A The Sliding Filament Mechanism Thick filaments: myosin Thin filaments: strands of actin molecules Contraction = formation of cross bridges between myosin and actin filaments Relaxation = no more cross bridges, filaments passively slide back into place  Skeletal Muscle contraction: sarcomeres A single myofibril consists of many sarcomeres Actin and myosin are the important proteins of muscle contraction Z lines: attachment points for actin. Muscle contraction: shortening many sarcomeres Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc. Skeletal Muscle Contractile Unit A sarcomere contracting  Steps of skeletal muscle contraction: 1) Signal for muscle contraction begins in frontal lobe of the cerebral cortex (if this is conscious movement). Neurons take the message from the brain, down the spinal cord and to the muscles. 2) Motor neurons stimulate muscles with Acetylcholine A, (a neurotransmitter) which diffuses to the muscle cell membrane and binds to protein receptors 3) Muscle electrical impulse is generated 4) Electrical impulse stimulates release of calcium ions into the cell cytoplasm, from the sarcoplasmic reticulum Nerve Activation of Individual Muscle Cell  Steps of muscle contraction 5) Calcium binds with troponin. Tropomyosin protein moves, exposing actin binding sites to myosin. 6) Energized myosin heads bind with actin, forming cross-bridges. After binding, the myosin head bends, bringing Z-lines closer together. Next ADP + P released. 7) ATP binds to myosin heads, causing them to release the actin filament. 8) Myosin heads split ATP into ADP + P and the head becomes energized. It can now attach to actin again if the muscle is still being stimulated to contract (back to step 6 above). Steps in sarcomere contraction Video: “Muscle contraction process”  Muscle Relaxation Nervous stimulation causes release of calcium ions Nervous stimulation ends à no more calcium ions released Calcium is pumped back into the sarcoplasmic reticulum. Calcium removed from troponin Actin-binding site covered by tropomyosin, myosin no longer can bind with actin. Sarcomere relaxes as z-lines move further apart. No nervous stimulation à no calcium ions à muscle relaxation  Energy Required for Muscle Activity Source of energy: ATP 1) ATP stored in cell used first by muscles (10 sec) ATP replenished by variety of means: 2) Creatine phosphate (stored, transfers phosphate to ADP) (25 more sec) 3) Stored glycogen (in muscles, broken down anaerobically or aerobically) (5 - 10 more min.) 4) Aerobic cellular respiration with glucose, triglycerides, proteins. Increased heart rate / breathing rate takes a few minutes: anaerobic respiration and oxygen debt often occur before that  Muscle fatigue Muscle fatigue: muscles cannot contract, even when stimulated by motor neurons to do so. Why? Low ATP supply + lactic acid that accumulates in muscle cells can lead to muscle fatigue. How do you stop fatigue? Taking deep breaths and resting (breaks down lactic acid and allows ATP to be replenished in muscle cells) Exercising aerobically only in the future. Motor unit One motor neuron stimulates more than one muscle cell. A motor neuron + all muscle cells it stimulates are a motor unit All muscle cells in a motor unit contract when nerve signal arrives. Skeletal muscles do not contract without nerve input. Movement: Fine control (eyes): less muscle cells (10) / motor neuron Brute strength (legs): many muscle cells (1000) / motor neuron  Skeletal Muscle Types Slow twitch fibers: break down ATP slowly, sarcoplasmic reticulum not as close to myofibrils à contract slowly. For endurance: more mitochondria, well supplied with blood (for oxygen / nutrient supply), stores oxygen in myoglobin (“red” muscle), low glycogen, low creatine phosphate. Better at long term, aerobic respiration. Fast twitch fibers: break down ATP quickly, sarcoplasmic reticulum close to myofibrils For power: more glycogen and creatine phosphate for generating ATP anaerobically, less mitochondria, less blood vessels, no myoglobin (“white” muscle). Better at short, anaerobic bursts of power.  Skeletal Muscle Types Muscles have both types, in different relative amounts. Muscles of back contracting for your posture: more slow twitch fibers. Muscles of the fingers: more fast twitch fibers. There are differences between people too, due to their genetics and the athletic training they have done in their life. Skeletal Muscle Types Slow twitch (red muscle): endurance, long duration contraction. (Running marathons, long-distance swimming and biking) Fast twitch (white muscle): strength, short duration contraction. (Sprinting, weight lifting) Exercise and muscles Fast twitch muscle for quick bursts of power / strength Strength training / Resistance training Short, intense workouts Builds: more fast-twitch myofibrils, stores more glycogen and creatine phosphate Builds more muscle mass / power Well developed fast twitch muscle à more muscle mass à more power, better ability to manufacture ATP anaerobically  Exercise and muscles Slow twitch muscles for endurance. Aerobic training / Endurance training Long, sustained work-outs Increases blood vessels to muscle cells, more mitochondria, more myoglobin created in slow-twitch muscles Builds endurance Well developed slow twitch muscles à efficient creation of ATP aerobically for long time periods. Benefits of exercise for muscles: Builds muscle mass (Strength training) Boosts endurance (Endurance training) Slows aging: regular exercise slows muscle deterioration (some cells lost, other cells lose myofibrils as you age, starting at about age 30). Muscle tissue burns up calories (like fat), and more muscle mass means it is easier to control your weight.  Comparison of muscle types Location / function: Skeletal: attached to bones with tendons for voluntary movement Smooth: artery walls, vein walls, digestive system, reproductive system, urinary system. Involuntarily controls blood vessel diameter and hollow organ movements Cardiac: heart, involuntarily pumps blood Comparison of muscle types Structure: Skeletal: Long, cylindrical and multinucleated Cardiac: Short, with blunt ends connected by gap junctions Smooth: Small spindle cells joined with gap junctions Cardiac muscles Gap junctions allow contraction signals to move between cells quickly, such that large numbers of cells (joined together) basically contract simultaneously. Smooth muscles Net – like arrangement of actin and myosin shortens and fattens smooth muscle cells. Always partially contracted, but do not fatigue, as they contract slowly and do not use up all their ATP.  Anabolic steroid use Anabolic steroids mimic testosterone, and cause more muscle protein synthesis. This results in larger, more-powerful muscles. Disadvantages to steroid use (men and women): Liver tumors / cancer, kidney tumors, severe acne, baldness (men): breast development, rage, shrinking testes, infertility (women): facial hair, deepened voice, menstrual cycle change  Muscular System Disorders Pulled muscles: some muscle cells pulled apart, if muscle becomes stretched too far Sore muscles: underused sarcomeres are damaged during exercise. Deteriorate and replaced, but hurt while this occurs Muscle cramps: muscles contract uncontrollably. Usually after heavy exercise, caused by a combination of factors including: ATP depletion, dehydration, ion imbalances and lactic acid build up.  Muscular System Diseases Tetanus: bacterial toxins over-stimulates nerves to muscles, resulting in constant contraction. Death by exhaustion or respiratory failure Duchenne Muscular dystrophy: sex-linked genetic disease in which muscles waste away. Death may occur as heart muscle or muscles for inhalation die, usually in the 20’s. The person is in a wheelchair in their teens.  http://www.schwarzeneggerbybutler.com/ Campbell, Reece, Mitchell, Biology,Benjamin/Cummings, Menlo Park, CA, 1999