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
Lactate dehydrogenase wikipedia , lookup
Adenosine triphosphate wikipedia , lookup
Gaseous signaling molecules wikipedia , lookup
Oxidative phosphorylation wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Basal metabolic rate wikipedia , lookup
Muscles Striated Cardiac Smooth Excitability and contractibility animations • http://www.dnatube.com/video/4875/Physiology-of-musclecontraction-and-relaxation • http://www.dnatube.com/video/1306/Role-of-myosincrossbridge-in-the-contraction-of-muscle • http://www.dnatube.com/video/1952/Sliding-filament-causescontraction-of-muscle • http://www.dnatube.com/video/4154/Cellular-mechanism-ofmuscular-contraction Striated muscle – sarcomere Striated muscle – sliding of contractile elements Striated muscle – motor unit Striated muscle – neuromuscular junction Striated muscle – myography, tetanus Muscle contraction •Twitch •Summation •Superposition Tetanus •Smooth - multiple summation •Undulating – multiple superposition Muscle strength • Muscle strength depends on the number of motor units recruited • Strength depends only on cross-sectional area 20 – 100 N per sq.cm Muscle cells cannot divide. Thickening is formed by duplication of myofibrils. • Muscle strenght is influenced – genetically – hormonally – testosterone, anabolics Muscle strength – tension/length curve, isometric and isotonic contraction Sources of energy for muscle contraction • ATP – maintains contraction for 1 to 2 seconds • phosphocreatine – 5 times as great as ATP, sufficient for 7-8 s contraction • Anaerobic Glycolysis – Enzymatic breakdown of the glucose to pyruvate and lactate liberates energy that is used to convert ADP to ATP, glycolysis can sustain contraction for about 1 min – Twofold importance of glycolysis • Reactions occurs in the absence of oxygen (muscle contraction can be sustained for a short time when oxygen is not available) • The rate of formation of ATP is 2.5 times as rapid as ATP formation with oxygen • Oxidative metabolism – the final source of energy – 95% of all energy used by the muscle Function of ATP ATP is necessary for • Muscle contraction – detachment of the head of myosin from the actin • Function of Na+/K+ pump • Function of Ca++ pump Physiological depletion of sources of ATP (reversible) – contracture, spasm, cramp Irreversible loss of all ATP – rigor mortis – Lack of energy for the separation of cross-bridges – Rigor is faster after muscle fatigue and exhaustion – Muscles remain in rigor until muscle proteins are destroyed by autolysis (15-25 hours) Muscle fatigue • Acute (recovery - within 24 hours) and chronic (may be followed by a complete exhaustion) • Decrease force of muscle contraction • Fatigue – in the neuromuscular junction • Accumulation of extracellular K+ may lead to a disturbance in depolarization, reduction of the amplitude of the action potential and conduction velocity – decreasing amounts of muscle glycogen – Accumulation of lactate – lower pH, increase of K+, stimulation of the free nervous endings – pain, edemas – exhaustion of ATP Striated muscle – twitch = types of muscles TYPE I - SLOW TWITCH Tonic muscles (darker: red) - Leg muscles TYPE II - (IIa & IIx) FAST TWITCH Tetanic muscles (paler: white) - Pectoral muscles longer contraction times (100-110 msec) shorter contraction times (50 msec) contain myoglobin (red) no myoglobin (white) continuous use muscles - prolonged performance for endurance performance ( marathoners) one time use muscles - brief performances for power & speed (sprinters) marathoner: 80% type I & 20% type II sprinter: 20% type I & 80% type II best in long slow sustained contractions best in rapid (short) contractions not easily fatigued easily fatigued more capillary beds, greater VO2 max less capillary beds smaller in size larger in size lower glycogen content higher glycogen content poor anaerobic glycolysis * predominantly anaerobic glycolysis easily converts glycogen to lactate wo O2 * predominant aerobic enzymes & metabolism some aerobic capacity higher fat content lower fat content more mitochondria - Beta Oxidation high fewer mitochondria- Beta Oxidation low poorly formed sarcoplasmic reticulum well formed sacroplasmic reticulum slower release of Ca = slower contractions quick release of Ca = rapid contractions tropinin has lower affinity for Ca troponin - higher affinity for Ca Muscle pain During exercise • Ischemic, hypoxic, accumulation of metabolites, pH • Fast in, fast out • Difficult to localize (muscle, bone, tendom, joint) • Referred pain (viscero somatic hyperalgesia) After exercise • Dull ache when moving or being palpated • Begins in 1-3 days and lasts for one week • Maximal isometric strength is not impaired • Does not correlate with muscle edema, plasma CK, inflammation markers Drugs that modify neuromuscular junction Botulinum toxin prevents acetylcholine release – spasms (torticolis) Methacholine, carbachol and nicotine – the same effect as Ach – not destroyed by acetylcholinesterase – long action – Ophtalmology (glaucoma) Muscle relaxants – general anesthesia – muscle relaxation. Curare (D-tubocurarine) blocks acetylcholine receptors w/o depol Succinylcholine is a depolarizing blocker Anticholinesterase drugs, neostigmine and physostigmine – reversible inactivation of acetylcholinesterase – accumulaiton of Ach – myasthenia gravis Organophosphate – chemical weapons – irreversible inactivation of acetylcholinesterase – cramps, respiratory distress, sweating and convulsions. Dandrolen blocks Ca realease from SR – malignant hypetermia Smooth muscle - structure actin and myosin no troponin, calmodulin instead Dense bodies – analog of Z-lines – attachment of actin filaments Actin – long filaments, 15 times as myosin • Contraction 30 times slower than that of sceletal muscle • constant power during contraction (isotonic line longer, since some contractile units have optimal overlapping of A&M at one length of the muscle and others at other length) Types of smooth muscles • Multiunite – discrete smooth muscle – single nerve ending – The ciliary muscle of the eye (parasympathetic control) – The piloerector muscles (sympathetic control) • Single-unit (visceral) – Hundreds to millions contract together – syncythial – gap junction – ions can flow freely – gut, bile ducts, ureters, uterus, vessels Contraction of smooth muscle • Initiating event in smooth muscle contraction is an increase in intracelullar Ca2+ ions cause by: – – – – Nerve stimulation Stretch of the fiber Hormonal stimulation Changes in the chemical environment of the fiber • Strength of contraction depends on extracellular Ca2+ • Removal of Ca2+ ions is achieved by calcium pump, calcium pump is much slower in comparison with a pump of skeletal muscle – longer contraction Mechanism of contraction • Beginning of contraction 4 Ca2+ bind with regulatory protein calmodulin Complex Ca-calmodulin activates enzyme myosin kinase (a phosphorylating enzyme) Light chain of of each myosin head (regulatory chain) become phosphorylated, the head has the capability of binding with the actin filaments • Cessation of contraction: When the concentration of Ca2+ falls bellow a critical level, all processes automatically reverse except for the phosphorylation of myosin head Enzyme myosin phosphatase splits the phosphate from the regulatory light chain Smooth muscle - contraction Smooth muscle – membrane potential Slow wave •Resting potential –50 to –60 mV •Spontaneous slow wave (some smooth muscle is selfexcitatory) •Slow wave can initiate action potentials (-35 mV) •The more AP, the stronger contraction Smooth muscle has more voltage-gated calcium channels and very few voltage-gated sodium channels than skeletal m. Importance of Ca2+ ions in generating smooth muscle action potential – phase plateau of AP, contraction Contraction without action potentials • In multiunite smooth muscle, Ca2+ ions can flow into the cell through the ligand-gated Ca2+ channel – ligand – acetylcholine, norepinephrine • Action potentials most often do not develop • Membrane potential do not reach a critical level for generating action potential because the Na+ pump pumps sodium ions out of the cell Regulation of smooth muscle Smooth muscle are regulated by autonomic nerves Nerve fibers do not make direct contact with smooth muscle fibers – they formed so-called diffuse junction Terminal axons have multiple varicosities, containing vesicules In the multiunite type of smooth cells, the contact junctions are similar to the end plate of skeletal muscle Sarcomere Nuclei Sarcoplasmatic ret. T-tubules A:M ration Length of Actin Actin fixing Conduction speed Contraction speed Resting potential Striated Yes Many Large Yes 2:1 Short Z-line High High -90mV Expandibility Small Smooth No One Small no (caveoli) 15:1 Long Dense bodies Low Low -60 mV, fluctuate large (10x) Regulatory protein Twitch End of contraction Consuption of ATP Connection Control Fatigue Striated Troponin Smooth Calmodulin, myosinkinase Fast & short Slow & long ↓ Ca ↓ Ca Spontaneous Myosinphosphatase High Low Synapse Varicosities Motoneurone pacemakers Autonomic NS humorální Mechanical Yes Almost not Neuromediator Source of Ca striated smooth Acetylcholine Acetylcholine (nor)Adrenalin Sarcoplasm ret Extracellular space