Smooth Cardiac Skeletal Location Around tubes Heart tissue attached to skeleton Moves stuff thru Heart beat pumps Moves body parts

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1 Biology Muscular system A. Type of muscles: Smooth Cardiac Skeletal Location Around tubes Heart tissue attached to skeleton Function Moves stuff thru Heart beat pumps Moves body parts tubes blood Appearance Spindle shaped Striated and branching Striated Nervous control Involuntary involuntary Voluntary Number of nuclei 1 1 many Contraction Slow to contract but sustained Rhythmic, relax completely btwn contractions (to prevent fatigue) Fast and short duration B. Functions of the skeletal muscles 1. Supports the body upright posture 2. Movement of bones and other body structures- ventilation, facial expression 3. Maintains constant internal body temperature -heat distributed thru body via bloodstream 4. Assist movement in veins and lymphatic vessels thru pressure of contraction of skeletal muscles 5. Protect internal organs in abdominal region 6. Stabilizes joints pads the bones and muscle tendons attach skeletal muscle to bone C. How skeletal muscles work with bones Skeletal muscles are inserted across a joint: origin = on stationary bone insertion = on bone that moves As skeletal muscle contracts and shortens, pulls bones towards each other Works in pairs, as 1 shortens, other lengthens D. Basic structure of skeletal muscles Whole muscle (surrounded by connective tissue, terminates in tendon that is across joint) Made up of Bundles of muscle fibers = fascicle Made up of individual Muscle fiber (AKA skeletal muscle cells)

2 Made up of Bundles of myofibrils Made up of Myofilaments myosin (thick filament) - actin (thin filament) Note: Names of skeletal muscles - not required Focus on Muscle Fiber: E. Muscle fiber components (diagram) A cell containing the usual parts but with specialized names 1. Sarcolemma plasma membrane of muscle fiber, forms T-tubules 2. T-Tubules (=Transverse tubules) Extension of plasma membrane into muscle fiber Conveys electrical impulse that causes release of calcium ions (Ca 2+ ) from sarcoplasmic reticulum 3. Sarcoplasmic reticulum Smooth ER of skeletal muscle fiber 4. Sarcoplasm Cytoplasm of skeletal muscle fiber that contains organelles and myofibrils 5. Myofibril Bunch of myofilaments that contract 6. Sarcomere Contractile unit of skeletal muscle fiber Located btwn Z lines 7. Myofilament actin and myosin Filaments that shorten causing muscle contraction sarcolemma mitochondrion sarcoplasm one myofibril skeletal muscle cell (fiber) myofilament Z line one sarcomere Z line T tubule sarcoplasmic reticulum nucleus

3 F. Sliding Filament Model of skeletal muscle contraction Thick filament composed of 1000 s of myosin molecules with globular heads Thin filament - 2 strands of actin intertwined with tropomyosin which has troponin molecules attached to it Sliding filament Model: 1. An electrical impulse is delivered to T-tubule system and travels to calcium ion (Ca 2+ ) storage sites in the sarcoplasmic reticulum 2. Ca 2+ is released and floods thru the myofibril and occupies molecule (troponin on tropomyosin rope ) on actin filament 3. Causes molecule to change shape and expose myosin binding sites on actin filament 4. Meanwhile myosin head has ATP molecule on it ATP hydrolyzes to ADP and P energy released during hydrolization activates Myosin head (and it becomes cocked ) 5. Activated globular heads of myosin (containing ADP +P) attach to exposed myosin binding site on actin forming a cross bridge 6. ADP and P are released giving energy to Myosin head which pivots causing a power stroke to occur 7. Actin filaments slide past myosin filaments. Since actin is attached to the Z lines, the sarcomere shortens and contraction occurs 8. Then another ATP molecule comes and binds to myosin head myosin head detaches, ATP again hydrolyses to ADP + P activating myosin head so it is ready for another cycle 9. For as long as Ca 2+ is present this will happen over and over again 10. When nerve impulse ends the Ca 2+ is actively put back into the sarcoplasmic reticulum G. Control of skeletal muscle fiber contraction: Neuromuscular Junction = where axons from motor nerves terminate at an effector (an organ or cell that reacts to a stimulus) or skeletal muscle fiber. Axon has an axon bulb that contains neurotransmitters in vesicles Electrical impulse travels down axon to axon bulb, causing exocytosis of neurotransmitters (NT) (in muscles this neurotransmitter is Ach acetylcholine) NT flood thru synaptic cleft and occupy receptor sites on the sarcolemma of the skeletal muscle fiber Causes the sarcolemma to generate an electrical impulse that travels down the T-tubules

4 This electric impulse goes down T tubules and travels to Ca 2+ storage sites and Ca 2+ is released starts cycle Focus on Whole Muscle: Motor unit Skeletal muscle fiber axon branch Axon terminal H. Definitions Motor unit = a nerve fiber with all the muscle fibers it innervates All or none law = all muscle fibers in a motor unit are stimulated at once therefore all contract or none contract Muscle twitch single contraction occurs Neuromuscular junction I. Single Muscle contraction: A single stimulus causes 1 muscle twitch Latent period btwn time of stimulus and before start of contraction Contraction -shortening of sarcomeres as actin slides over myosin filaments Relaxation crossbridges btwn actin and myosin filaments detach and muscle fiber returns to its former length J. Sustained Muscle contraction Motor unit given a series of stimuli rapidly Fiber cannot relax before it starts contacting again Summation = increased muscle contraction until max sustained contraction (tetanus) is reached Cannot relax until energy stores are depleted then fatigue occurs and contraction collapses even though stimuli have not stopped occurring.

5 Muscle tone = some motor units in muscle are contracted at all times, but not enough to cause movement In a whole muscle, usually some contracting and some relaxing so whole muscle does not fatigue allows sustained contraction to occur K. Energy for skeletal muscle contractions 1. Fuel sources: a) Glycogen stored in muscle b) Fat c) Blood glucose in circulating blood d) Plasma fatty acids 2. Sources of ATP (energy) for contraction: Muscles store little ATP therefore rely on 3 ways to make more ATP a) Creatine Phosphate pathway (CP Pathway) - anaerobic Creatine phosphate is a hi energy molecule that is stored in skeletal muscle tissue. Creatine phosphate in the muscle cells break down to provide phosphate and energy to convert ADP back to ATP Occurs at sliding filaments therefore quickest source of ATP Formed only when muscle resting only limited amount stored. Extra info -interesting but don t need to know

6 Where does creatine phosphate come from? When demand for energy is low the ATP produced by respiration is used as a source of phosphate and energy to produce creatine phosphate. This acts as an energy store in the muscles. Some creatine is broken down into creatinine which is a waste product transported to kidneys and excreted in urine. creatine can be reconverted to creatine phosphate but this takes a bit of time also creatine phosphate is made only when a muscle is resting Intense activity lasting longer than ~5 sec can also make use of fermentation as a source of ATP b) Fermentation anaerobic (w/o O2) Produces 2 ATP molecules from the anaerobic breakdown of glucose to lactate this method is most likely to begin with glycogen as glucose source Produces 2 ATP per glucose molecule therefore inefficient, but fast acting Causes buildup of lactate (lactic acid) that causes short term muscle ache Oxygen debt occurs and continued intake of oxygen after exercise stops is required to return cells to original energy state Lactate is transported to liver where 20% is broken down to CO2 and H2O. ATP gained by this respiration is then used to reconvert 80% of lactate to glucose then glycogen. c) Aerobic Cellular Respiration Requires oxygen (aerobic) Occurs in sarcoplasm and mitochondria Glucose + O2 ATP + CO2 + H2O Slowest but most efficient, ~32 ATP per glucose molecule Cell respiration can make use of glucose from breakdown of stored glycogen, glucose from blood, and/or fatty acids from fat digestion Anaerobic Anaerobic Aerobic Creatine phosphate glycogen Glycogen or Fatty acids O 2 fermentation Creatine lactate CO2 + H2O ATP ATP ATP

7 L. Homeostasis and the skeletal and muscular systems What the skeletal and muscle systems do in regards to homeostasis 1. Both systems produce movement: Skeletal muscles pull on bones help us respond to changing environment (i.e., run away from the sabre tooth tiger!!) Skeletal muscles associated with jaw and tongue allow us to eat and drink Smooth muscle moves food thru digestive tract and blood through vessels Cardiac muscle propels blood thru body Skeletal muscles help move blood in veins and lymphatic vessels(=skeletal muscle pump) 2. Both systems protect body parts: Skeleton protects soft internal organs Muscular system pads bones+ protects abdominal organs 3. Bones store and release calcium / muscles use Ca 2+ (=calcium) Always need a store of calcium in blood Muscles need calcium to contract Skeleton acts as a reservoir for storage of Ca 2+ If blood Ca 2+ falls, bone tissues make Ca 2+ available to the blood 4. Blood cells are produced in bones Red bone marrow is where all blood cells are produced Red blood cells are oxygen carriers in blood White blood cells defend body 5. Muscles help maintain body temperature, blood transfers heat around the body Smooth muscle in blood vessels that go to skin constrict and reduce amount of blood near skin surface conserving heat in core of body. Shivering makes muscles work produce heat