Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
CH 11 muscle tissue types of muscles microscopic anatomy of muscles how muscles work three kinds of muscles skeletal – voluntary smooth – involuntary cardiac - involuntary muscles are/have excitability – generate electrical changes conductivity – wave of excitability contractility – shortens extensibility – can stretch without breaking elasticity – move back to zero point - a muscle is a complex structure - it has an origin and an insertion - a muscle consists of many fascicles - a fascicle consists of many muscle fibers - a muscle fiber consists of many long & thin myofibrils - the functional unit of a myofibril is a sarcomere - a myofibril has many sarcomeres - a sarcomere consists of many thick and thin myofilaments - a sarcomere is able to contract and return to normal length -many myofilaments and associated organelles form a myofibril -each myofibril is surrounded by a sarcoplasmic reticulum -T tubules penetrate deep into the endomysium covered myofibril a group of myofibrils surrounded by a sarcolemma = muscle fiber -groups of muscle fibers surrounded by perimysium form fascicles -numerous fascicles surrounded by epimysium form a muscle a muscle fiber has a very developed SR so a muscle contains many thousands of SR sliding filament theory thick filaments – myosin heads (light and heavy) in an inactive form each attached to a long twisted tail with a flexible portion and a longer portion linked to other longer tails, heads are able to hydrolyze ATP and release the energy needed to allow the myosin head to change position and link to troponin on thin filament thin filaments - two intertwined strands of globular actin - two strands of tropomyosin which cover the active sites on the globular actin - calcium binds to troponin on tropomyosin causing exposure of active sites on globular actin the whole process nerve impulse – causes calcium to enter synaptic knob - ACh is released – Ach binds to sarcolemma receptor – causes Na/Ca channels to open – sarcolemma reverses polarity – creates action potential – reaches T tubules = Ca released – Ca enters muscle fiber – binds to troponin on thin filament – thin fiber changes shape – active actin sites now exposed – myosin ATPase an enzyme on myosin splits ATP - energy allows myosin head to bind to actin & bend into a high energy position = power stroke - power stroke – myosin releases ADP + P - bends into a low energy position, - picks up ATP, & releases actin= recovery stroke –energy from ATP used to attach to actin – same happens over and over by thousands of myosin heads all acting at the same time & in a coordinated fashion= Z line come closer= contraction -nerve impulse stops - AChE breaks Ach-Ca reabsorbed by sarcoplasmic reticulum - active sites covered - no more contraction - plasma membrane of muscle fiber = sarcolemma - cytoplasm of muscle fiber = sarcoplasm - the protein cords which make up the sarcomeres = myofibrils - muscle fibers are rich in glycogen & myoglobin - some myoblasts remain as = satellite cells (stem cells) - smooth endoplasmic reticulum is called the sarcoplasmic reticulum - sarcoplasmic reticulum has channels called terminal cisternae which cover the myofibrils from side to side - the sarcolemma sends a tube called transverse (T) tubules associated with two terminal cisternae which travel with the terminal cisternae from side to side - the SR is a reservoir for Ca needed for sarcomere contraction smooth muscle no striations, 1 nucleus, no T tubules, no Z discs, no sarcomeres, no myofibrils, scant sarcoplasmic reticulum small groups of myocytes for fine control autonomic (not always innervated) NE sym & Ach parasym synaptic vesicles have multiple varicosities no motor end plate receptors spread over muscle surface slow response long to fatigue very energy efficient mitosis, hyperplasia, move things, hold things contraction and relaxation NE or ACh binds to receptors and open Ca channels Ca binds to calmodulin on myosin activates myosin light chain kinase adds phosphate to regulatory protein and activates ATPase myosin performs repetitive power stroke and recovery stroke thick pull thin in & attached cytoskeleton and dense bodies cause muscle cell to shorten and twist removal of Ca is slow so contractions long latch mechanism hold cell contracted without more energy cardiac muscle heart – regular rhythm – non stop – resists fatigue cells contract in unison – contract long enough to pump blood striated – short and thick cardiocytes – gap junctions intercalated discs (tight junctions) – small SR – large T tubules pacemaker – ANS stim= ↑or ↓ of contr. and/or strength mostly aerobic, myoglobin↑, glycogen↑, large mito, nerve muscle relationship some muscles contract spontaneously but most muscle fibers contract as a response to a nerve stimulation the nerves which stimulate a muscle are called somatic motor fibers whose cell bodies are in the brainstem and spinal cord a neuron has a few to many terminal branches which end on individual muscle fibers all of the muscle fibers innervated by the terminal branches of a neuron are called a motor unit small(fine control) = 3 - 10 large(coarse) = average 200 100 neurons innervate 1000 muscle fibers 1 neuron innervate 1000 muscle fibers different groups of fibers within a muscle are innervated by different motor units this allows for continued contraction as one group of fibers fatigue others continue to function words we need to remember and understand somatic motor fibers neuromuscular junction synaptic cleft acetylcholine (ACh) acetylcholinesterase(AChE) motor unit motor end plate Schwann cell ACh receptors synapse synaptic knob synaptic vesicle junctional folds nerves and muscle cells are described as electrically excitable this is based on the difference in concentrations between the intercellular fluid ions compared to the extracellular fluid ions the inside of the cell has more negative ions than the outside of the cell this difference in polarity is referred to as a resting membrane potential the inside of the muscle cell compared to the fluid outside of the cell is -90 mV (milli volts) stimulation of a nerve or muscle causes - channels open in the plasma membrane - Na rushes in from high to low concentration - the positive Na ions depolarize the cell (goes from – to +) - Na channels close and K channels open - K leave the cell and repolarizes and hyperpolarizes the cell - this cycle of de and re polarization is an action potential - so much K enters the cell that the RMP drops to more than -90 mV and the cell becomes refractory (cannot initiate another action potential until RMP returns to -90mV) muscle relaxation as the local potential becomes an action potential there is no more need for calcium at the initial site but there is still a need for calcium until the nerve stops firing at this point the calcium channels close calcium is reabsorbed by the sarcoplasmic reticulum and large amounts of calcium are stored in the SR bound to a protein calsequestrin and stored in the SR without Ca precipitation length strength relationship too contracted = weak response to stimulation too stretched = weak response to stimulation optimum length = strong response to stimulation at optimum length the body maintains partial contraction known as muscle tone not all stimuli result in an action potential or muscle contraction too much or too little stretch = less than maximum contraction fatigued muscle = less than maximum cold muscle = less than maximum too little hydration = less than maximum long stimuli intervals = less than maximum intensity vs frequency a weak stimulus activates a twitch with weak or no contraction stronger stimulus activates more fibers = weak or no contraction stronger stimulus activates more fibers = weak or small contraction strong stimulus activates more fibers = small to strong contraction stronger stimulus activates more fibers = strong contraction as the stimulus increases more motor units are recruited and more muscle fibers are stimulated resulting in stronger contractions known as MMU multiple motor unit summation low frequency stimulation = muscle relaxes completely before next stimulus higher frequency stimulation = before one twitch comes to rest the next stimulus adds to the previous twitch – strength can build quickly to more than a single twitch very high frequency = no relaxation, twitches fuse to tetanus isometric and isotonic scientists describe 4 different types of contractions isometric - isotonic - concentric - eccentric isometric = contraction without a change in length isotonic = contraction with a change in length but no change in tension concentric = muscles shorten as it maintains tension eccentric = muscle lengthens as it maintains tension where do muscles get the energy to do the work that they all do? ATP aerobic and anaerobic with oxygen or without oxygen resting = aerobic respiration using fatty acids during exercise = anaerobic, short term, & long term - if still active = homeostasis catches up & oxygen becomes available & aerobic respiration takes over (long term energy) - the body accommodates over 3 to 4 minutes & energy production levels of at a steady state – 90% of energy is aerobic for exercise of more than 10 min – up to 30 minutes energy is from glucose & fatty acids and then only fatty acids after glucose stores depleted fatigue K concentration ADP/P accumulation lactic acid accumulation fuel depletion ** - glucose and glycogen depletion electrolyte loss ** - too much sweat, too little intake central fatigue ** - NH3 accumulation inhibits CNS signals XS post exercise oxygen consumption (oxygen debt) oxygen is required for synthesize ATP ATP needed to regenerate creatinine phosphate regeneration of myglobin liver need oxygen to destroy lactic acid raised body temperature increases need for oxygen slow and fast twitch muscles slow = small motor units, long duration of twitch, excitable, weak strength, aerobic, fatigue resistance, many organelles, many BV, slow ATP hydrolysis, slow oxidative, red color fast = large motor units, short duration of twitch, less excitable, strong contraction, anaerobic, easy fatigue, fewer organelles, white color, rapid ATP hydrolysis, fast glycolytic, few BV, extensive sarcoplasmic reticulum, much glycogen, high CP, most muscles have both types in various amounts type of muscles you have may determine choice of activity muscle strength depends on size = thickness fascicles = arrangement/orientation of fibers motor units = larger generate more strength multiple summation = involve more motor units temporal summation = increased frequency increases strength stretch = optimum stretch results in optimum strength fatigue = more rest produces more strength resistance exercise = contraction against a load, results in more and thicker myofibrils, does not increase endurance endurance exercise = improves resistance against fatigue, more organelles, better use of oxygen, more BV, increases skeletal strength, does not increase strength to increase both strength and endurance requires cross training