PSL 250 Week 7 Lectures
PSL 250 Week 7 Lectures PSL 250
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This 9 page Class Notes was uploaded by Ren K. on Sunday October 16, 2016. The Class Notes belongs to PSL 250 at Michigan State University taught by Dr. Patrick Dillion in Fall 2015. Since its upload, it has received 8 views. For similar materials see Introductory Physiology in Physiology at Michigan State University.
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Date Created: 10/16/16
PSL 250 - Lecture 19 - Muscle Metabolism and Control Muscle Energy use ● Progressive use of energy resources. Phosphocreatine ● Supports about 20 seconds of full activity. ● PCr + ADP = ATP + Cr by creatine kinase reaction. ● ATP = ADP + Pi by myosin ATPase ● PCr = Cr + Pi net reaction. ● Pi inhibits myosin ATPase ● (M⚫ADP⚫Pi = M+ADP+Pi) Glycolysis - 10 Rxs ● ~2 minutes of energy use. ● Glucose and glycogen in muscles = pyruvate = lactate. ● No oxygen use. Oxidative Phosphorylation ● Krebs cycle and electron transport system. ● ~2 hours of energy support. ● Pyruvate converted to CO2 ● Oxygen used ● Carbohydrate loading increases glycogen storage, increased by up to 30%. ● Don’t go too fast at any one time / do not allow hydrogen ion concentration to get too high (hydrogen ion high = lose motivation to go fast) Fiber Types ● Variations in the fiber type even within same muscle. ● Controlled by motor neuron - most muscles are mixed. Red Fibers ● Also called slow oxidative. ● High mitochondrial levels - slow myosin ATPase - slow speed. ● High energy capacity, low energy use - no fatigue White fibers ● Also called fast glycolytic ● Few mitochondria - fast myosin ATPase - fast speed. ● Low energy capacity - high energy use - easily fatigued. Hypertrophy ● Larger cells not more cells - hyperplasia. ● High intensity, high force exercise needed for maximum effect. Filament Number ● High intensity exercise causes micro damage to filaments. ● Disassembly of tangled filaments increases free myosin and causes pain. ● Free myosin causes increase in expression of filament forming enzymes - more filaments, bigger cells. ● ⚫ ● Young - 48 hours cycles (24 dissasembly, 24 assembly). ● Elderly - 72 hour cycle, risk? ○ Simplest way to increase blood pressure - lift heavy weights. ○ Seriously increase the risk of stroke. Testosterone Dependence ● Filament production optimized by testosterone. ● Females with normal endocrinology cannot maximize muscle size. Atrophy ● Reduction in the size of muscle fibers. ● Not loss of muscle fibers Disuse atrophy ● Muscle immobilized - loss of filaments. ● Easily reversible Denervation ● Motor neuron damage causes fiber to lose filament. ● Not reversible - loss of myotrophic factor from neuron. ● Electrical stimulation decreases rate of atrophy. Stretch Reflex ● Muscle length information ● Monosynaptic reflex - knee jerk. ● Activation of afferent neuron produces reflex response ● No control by upper CNS. Muscle spindles ● Stretch receptors in muscles. ● Groups of intrafusal fibers in connective tissue capsule. Intrafusal Fibers ● Each fiber contains muscle section and stretch receptor section. ● Fibers activate afferent neurons from receptor section of fiber. ● Fibers also receive efferent gamma motor neurons to muscle section of fiber. Nuclear bag fibers ● Have larger central portion of receptors. ● Pull on these - adapt. Dynamic Response only ● Detects change of length ● Highest response when muscle rapidly stretched ● Decreased response as stretch is sustained ● Very rapid adaptation. Nuclear Chain Fibers ● Smaller set of receptors parallel to nuclear bag fibers. ● Very narrow center file with vesicles within the center. ● When you pull on these, they do not ‘adapt’ ● Send signal to brain on what position you are in. Static Response ● Detects fiber length. ● Response proportional to the position - slow adaptation. Gamma motor fibers ● Efferents to intrafusal fibers ● Contract muscle portion of intrafusal fibers. Coactivation ● Dual activation of alpha and gamma motor neurons ● Alpha motor neurons contracts muscle fibers ● Gamma motor neurons contract intrafusal fibers ● Keeps muscle spindles taut Reciprocal Innervation ● Inhibition of paired muscle when stretch reflex occurs. ● Afferent neurons leads to interneuron causing an IPSP to paired alpha motor neuron. Golgi Tendon Organ ● Muscle force detectors ● Receptors in tendon - afferent input proportional to muscle force. ● At very high forces, GTO sends IPSPs to alpha motor neurons. ● Has a protective effect. PSL 250 - Lecture 20 - Smooth Muscle Smooth muscle structure ● Small cells are linked via desmosomes. ● No striations. ● Filaments are parallel but not in register. Filaments ● Thin filaments: actin and tropomyosin, no troponin. ● Thin filaments are in groove, no AM blocking. Dense bodies ● Smooth muscle equivalent to z lines. ● Anchored to cell membrane, also in interior. ● Thin filaments attach here and pull ends of cell. Tone ● Force with no stimulus. ● Ca++ leaks in and partially activates smooth muscle. ● Important in BP maintenance, holding cavity contents. Smooth muscle contraction ● Different control mechanism than striated muscle. ● Ca++ also activates. Calcium sources ● Most: through channels across cell membrane. ● Some: small SR, released by IP3 Myosin Light chain kinase ● Ca++ activated. ● Adds phosphate to myosin light chains. ● Activate myosin ATPase for shortening and Force. Force Generation ● Myosin *ADP * Pi (with MLC-P) binds actin - ADP and Pi leave. ● Myosin twists, generates force. ● Filaments slide to reduce force. ● This part is similar to striated muscle. Myosin light chain phosphatase ● MLCPase removes phosphate from myosin light chains. ● Low Ca++ turns off myosin and causes relaxation. Latch ● Removal of Pi from light chain when AM attached decreases M detachment rate. ● Maintains force with little energy use. ● ALlows BP maintenance with low energy use, allows upright position. Smooth muscle types ● Vary with function; emptying cavities or maintaining force. ● At a particular time have to contract eventually. ● Other muscles need to have a modest contraction maintained, for decade over decade - like for Blood Pressure. Visceral (Single unit) SM ● Also referred to as single unit muscle. ● When one contraction occurs, contraction would spread to other cells. ● Stomach GI tract urinary bladder ● Linked by gap junctions, activating APs. ● Will only contract when AP is occurring. ○ APs take on a pattern - stomach contracts once every 20 seconds. ○ Starts very high and then moves downward. ○ Get phasic activity causing rhythmic contractions. Neural effects ● on Visceral occur from both parasympathetic and sympathetic nerves. ● Release acetylcholine as the neurotransmitter, causing contractions to occur. ● Both have same structure ● Main axon of the neuron comes down and then spreads down into the vericosities - widening area. ● Vericosities contain the vesicles that have the neurotransmitters in them with acetylcholine with parasympathetic and neural epinephrine for the sympathetic. Multi-unit smooth fibers ● Have no gap junctions. ● No action potentials at all. ● Membrane potential varies based on hormones or on level of neural activation. ● Amount of open calcium channels impacts how depolarized it is. ● Causes contraction. ● What this causes - average force that maintains things at a controlled level. ● Entirely sympathetic - for multi units. ● Sympathetic response causes the release of norepinephrine. Tone ● Leakage of calcium in through the membrane. Latch mechanism ● Allows you to maintain contractions with very low energy cost. ○ Example: blood pressure and eye focus. PSL 250 - Lecture 18 - Motor Units Motor Unit ● Motor neuron and muscle fibers it innervates. ● Motor neuron AP activates all the fibers in a motor unit Recruitment ● Small MUs first, then the larger motor units. ● Allows gradation of force. ● Maximum force requires all MUs active simultaneously Asynchronous Recruitment ● For submaximal forces - rotate activation of MUs. ● Maintain force - cannot simultaneously optimize force and continuous activity. Twitch ● Single AP = single muscle activation ● 1 neural AP leads to one muscle AP leads to one twitch. ● Sub-maximal force - not enough Ca++ reaches all troponin for full activation Tetanus ● Summation of twitches - many APs ● Enough Ca++ so that all myosin heads reach actin. ● Unrelated with the bacterial infection Tetanus. Length- Tension Relation ● Lo - Muscle length at which maximum force occurs ● Resting skeletal muscle length is near Lo ● Not force ™ - Lo is a length. ○ Thats is a test question ™ . Falloff at Long lengths ● Reduced overlap of thick and thin filaments. Falloff at Short Lengths ● Thick filaments compression against the z line. ● Thin filaments overlap and interfere with each other. ● Reduced Ca++ release Force-Velocity Relation ● Heavy loads can only be moved slowly. ● Light loads can be moved quickly. Inverse Relations ● High force (load) = low velocity ● Low force (load) = high velocity ● Hard to throw a 100 kg stone fast vs 1 kg stone Stretched muscles ● Stretching before activation (windup) uses top of L-T curve. ● Better force maintenance. ● Also, activating stretch reflexes causes the reflex contraction of stretched muscles. Power curve ● From F-V Curve. ● Power = F x V ● At F = 0, P = 0; At V = 0; P = 0. ● At all others, F*V is positive, and must have maximum. ● 0.25 Fo has optimum power output. ● Skeletal muscles - 0.25 Fo most optimal to do work. ● Injuries occur because feedback loops are so close to being maximal for sprinting. ● Ripped muscle occurs because one paired muscle is out of sequence.
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