PHIS 206 1st Edition Exam 2 Study Guide Muscle 3 Major categories o 1 Skeletal Voluntary Striated Muscle o 2 Smooth Involuntary Visceral non striated o 3 Cardiac Heart Muscle All Muscles contract Muscle is a mechanical device o Requires energy Real device efficiency is NOT perfect doing work generates heat Examples Shivering when cold Exercise rises body temperature Voluntary muscles can be consciously controlled Skeletal Muscle Known since mid 19th Century that it has striations Striations are made from the arrangement of proteins Vocabulary Cell Membrane Sarcolemma Smooth covering of the cell that dips into the cytoplasm t tubules Endoplasmic Reticulum Sacrcoplasmic Reticulum Releases calcium into the cytoplasm This release of calcium causes muscle contraction Muscle Cell Muscle Fiber Muscle fibers bind together to form a muscle Within it are Myofibrils Visible manisfestations of proteins long cylindrical Proteins 1 Actin Thinner known as thin filaments 2 Myosin Thicker known as thick filaments Overlap one another They are attached to one another acto myosin fibers Gives rigidity makes muscles hard to pull apart regular repeating array lengthwise along the muscle Cross bridges molecular connections between thick and thin filaments near the tip of the filaments o Give muscle cell its longitudinal rigidity Sarcomere length about 2mm Sarcolemma smooth covering Sliding Filament Mechanism When Muscle fiber contracts the thick and thin filaments stay the same size they just get closer to one another The ends of the thin and thick filaments become closer Energy source is ADP Provides energy for contraction shortens muscle Gets energy from mitochondria Muscle cells have lots of Mitochondria Two things Muscle can do Isometric Contraction Can generate force without Cells shorten but muscles don t Force low velocity high 1 Isotonic Contraction Can shorten without generating force At same tension Rarely happens in pure form mostly approximation Generate motion at a constant force Movement of limbs Example Piano player starts with isometric then turns to isotonic Force high velocity low Physical Definition of Work Move Force through a distance By definition Isometric does no work Power Rate at which you do work By definition Isometric doesn t generate power Maximum Ability to do work at high rate 1 3 of 0 velocity and max velocity Length tensions Diagrams Tension Length Passive Tension o As you increase length you increase tensions o Not active no energy required o Elasticity stretchability of muscles Tension Active Tension I electricity I I I I Length Tension will increase reach a maximum then decline With the little tension the ends of the thick and thin filaments are far apart At maximum tension the ends of thick and thin filaments are completely aligned Muscle Tetany if you stimulate a muscle again before it s relaxed it can stay contracted o Muscle contracts and stays contracted Tetanic Stimulation sensation that leads to tetany o Average 50 55 stimulations per second in human skeletal muscle Incandescent light flickers but we can t see it o Electric current in US 60 stimuli per sec cycle current o Most of the rest of the world 50 stimuli per sec Reason US does this Historical Meaning it was believed that anything less than 60 cycles then the lights would flicker Truth is that you can see no flickering with cycles all the way down to around 40 cycles Twitch either it contracts or it doesn t NO halfway Neural Control Helps to make fine movements o Brain sends out instructions to how many Motor Units to send out Motor neuron Fire tetanic stimuli to cause muscle contraction Releases Ach onto the motor endplate Ach binds cholergenic receptors onto the endplate Generates action potential in muscle Vary strength of contraction by increasing or decreaseing the number of motor neurons firing Motor Unit 1 Motor Neuron all the muscle cells it stimulates 1 Motor Unit innervates more than one cell Muscle cells are innervated by only 1 neuron small motor units allow for finer graded contractions Motor Nerves that make fingers work have small motor units In thigh the motor units include several hundred cells generate great power Reason we play piano with fingers not heels Smooth Muscle Can shorten in every direction Different from striated muscle Doesn t have striations Actin Myosin present but elements are not lined up in registered order so do not see the visible manifestations of striations Smooth Muscle cells are electrically connected to one another Transmit depolarization to cells Immediately around it which sends a wave propagated out Transmit action potentials from one to the next Strength are controlled by hormones and Neurotransmitters Does contract Spontaneously Skeletal Muscle doesn t Smooth have membranes that are leaky so when a smooth muscle cell rests it never has a stable action potential so it drifts up until cell depolarizes Reoccur at regular intervals The rate of leakiness can be modified by neuron or hormone Muscle use energy to do work o Uses ATP for energy o Source for ATP come from Mitochondria o Aerobic Respiration Continue to do for long time use oxygen in Mitochondria to produce ATP can generate 2 3 of oxygen amount If me need more than 2 3 use anaerobic pathway use ATP that comes from glucose By product Lactic Acid Lactic Acid causes muscle fatigue muscle refuses to contract anymore When we reduce level of activity anaerobic comes in and replaces oxygen gets rid of lactic acid If we lack oxygen metabolites do not have enough substrates to metabolize all the way to carbon dioxide Instead it only metabolizes to lactic acid which is more acidic and causes pain in sustained use Muscle Fiber Types Red Muscle Looks dark Lots of Myoglobin Red protein Related to hemoglobin Also binds to oxygen Carry around a reservoir of oxygen o Allows for oxygen to be used even when oxygen intake is decreased o When you work to the point where you do too much you can go a little longer because of stored oxygen slow twitch doesn t contract as rapidly myoglobin takes up more space less space for actin and myosin operates much longer White Muscle Not able to sustain aerobic exercise as long less Myoglobin more Actin Myosin Means more power but because no reservoir of oxygen it fatigues quickly Actin and myosin are not arranged in parallel Skeletal muscle only shortens in the long direction Examples Bird flying 3 or 4 power strokes and then soar White Muscle Red Muscle Leg muscles capable of