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Ex phys lecture notes - muscle.docx

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Department
Kinesiology
Course
Kinesiology 2230A/B
Professor
Glen Belfry
Semester
Fall

Description
Exercise Physiology: Muscle Function During Exercise Lecture 1 Muscle Structure  more than 430 muscles in body -opposing pairs – for every movement about a joint you need an opposite muscle to move it back to resting position Types of Muscles Skeletal - voluntary muscle; controlled consciously - has origin and insertion on either side of a joint - SO, FOG, FG, : ST, FTa, FTb, - Type 1, 11a,11b - fast glycolytic oxidative fibers  ability to produce energy oxidativley while contracting at a faster freq than SO, can also produce energy glycolytically – can increase number of these fibers through training – will not produce as much lactic acid, so wont fatigue as soon - fast glycolytic fibers – very little oxidative capacity – can produce a lot of power and speed but will produce lactate, high rates of energy production Cardiac - Controls itself with assistance from the nervous and endocrine systems( Adrenal gland) - Only in the heart - Ability to depolarize spontaneously - Nervous and endocrine produce hormones to increase or decrease heart rate based on whether or not they are being released or removed from the blood stream - Has the ability to contract but have origin and insertions on adjacent myocardial cells Smooth - Involuntary muscle; controlled unconsciously - In the walls of blood vessels and internal organs - Surrounding the vasculature Overview - Muscle fibers are a single cell made up of myofibrils - Can do experiments on single muscle fibers – they are very long and thin, able to function (shorten) as a single cell Connective Tissue  Epymisium: tissue surrounding the whole muscle.  Perimysium. Surrounds approx 150 fibres., enclose many muscle fibers  endomysium-separates individual fibres, connective tissue surrounding indiv muscle fibers within cell itself  Fasiculus: group of fibres 1  the connective tissues from the epymisium/ perimysimn/endomysim come together as the tendon that attaches to the bone (peripheral of the whole muscle)  Two attachments the origin(non-movable) and the insertion (movable)  Connective tissue all coalesces in the tendon which transmits force to bone  Several scaffolding proteins also involved in muscle structure  Scaffolding proteins – are woven within the myofibril matrix itself to give it strength and form Scaffolding Proteins  scaffolding proteins help muscles keep their shape – provide structure and form  binding sights for proteins involved in signaling cascades  specific scaffolding proteins – titin and nebulin  titin = associated with the myosin  nebulin = associated with the actin filaments  give form and strength to the muscle = also binding sites for proteins involved in signaling cascades  signaling process that allow changes to occur are in the titin and nebulin areas – generates more force to allow actin and myosin to contract Muscle Dystrophy - actin filaments ability to change in length associated with dystrophin dimmers  allow force from shortening of actin and myosin to be transferred to the whole muscle - bound to exterior membrane - MD – degenerative disease  disease in the dystrophin dimers and actin area begins to disintegrate - Actin and myosin filaments are still functional but lose link to the outer membrane of the cell and lose the ability for the whole muscle body to shorten – tend to lose muscle function - Shortening isn’t relayed through the muscle and eventually to the bone itself 2 An Individual Sarcomere - Has a Z-line on either side – anchor point to an adjacent sarcomere - Depending on the activity of the muscle dictates how much force needs to be produced and how many sarcomeres need to contract - Even if only some sarcomeres are contracting the force is still transferred to the whole muscle - M-line – anchor point can have shortening from Z-line to M-line Muscle Fibre Cross-section - Each fiber can work independently depending on the amt of movement that needs to be generated - Recruit less fibers for smaller movements - One muscle fiber can be 12 cm – very long and thi\n Contractile Proteins Thick filament = myosin - Heads and tails bound to myosin protein chain - The heads swivel to allow the muscle to shorten Thin filament = actin, troponin, tropomyosin - Braids of tropomyosin surrounding the actin - myosin heads bind to the binding sites on the actin hidden by the troponin - troponin move off of the binding sites to allow myosin heads to bind Innervation - spinal nerves off of the spinal cord - cells bodies receive nervous impulse - movement of depolarization eave through the nerves and to the muscle - can have faster nerves or slower nerves - specific nerve to specific target muscle - interface btwn nerve and muscle itself – transfer or stimulus to have effect on actin and myosin proteins Initiation of Muscle Contraction  nerve is depolarized  action potential moves along nerve  action potential crosses neuromuscular junction  action potential enters muscle and causes calcium release 3 Lecture 2 Action Potential  action potential – rapid and sustained depolarization of the nerve membrane  membrane must first reach threshold before action potential can occur  action potential is propagated along the nerve  depolarization = change in polarity from negative to positive, positive to negative  need rapid freq so action potential can occur  must reach threshold for action potential to occur Resting Membrane Potential - negative charge within the cell, positive charge outside cell - positive charge associated with sodium - in the cell have conc of potassium – which is positive - but net diff within the cell is slightly negative - negative charges in the cell are associated with the membrane proteins - need change in polarity from inside to outside the cell Action Potential - as action potential moves along the fiber – affects voltage gated sodium channels - channels open and have influx of sodium into cell - permeability of K to cell mem is reasonable high - fast influx of sodium as the voltage changes leads to positive influx of sodium and positive charge that is already in cell - depolarization occurs - movement of K outside the cell thru K channels and increased permeability of mem already for K - give balance of neg inside the cell and pos outside the cell - from polarity perspective – neg inside and pos outside – same as at rest - Na/K pump – requires ATP, pumps sodium outside cell and K back into the cell - Propagation – influx of Na, affects area near the channel and 4 in areas adjacent to the nerve tissue - Many Na channels in the mem, change in polarity causes opening of adjacent Na channels - Change in polarity isn’t just specific to area of the sodium channel - Voltage change in polarity - Causes opening of the next Na channel - Prop of action potential along the nerve mem Nerves - Cell body, axon, nerve endings - movement of AP along axon - myelinated fibers and non myleinated fibers - insulation qualities of myelin sheath – major function is to enable faster prop of AP through the axon - non myelinated have slower AP prop speeds - myelin sheath itself is 80% lipids and 20% protein - brief distances btwn myelin areas = nodes of ranvier – AP jumps from node to the next node Nerve Function  action potentials are faster in myelinated fibres compared to unmyelinated fibres  Myelin is composed of about 80% lipids and about 20% protein. Insulation qualities. Saltatory Conduction  myelinated axons, action potentials do not propagate as waves, but recur at successive nodes and in effect "hop" along the axon  period of time as the AP travels along the nerve where you are unable to generate an AP  when the change in charge occurs, when polarity is reversed – you cant elicit an AP = refractory period (very short)  continuous conduction in non-myelinated fibers, salutatory conduction in myelinated fibers  salutatory – for when you have long distances for messaging to travel in nervous system, or you need very fast action of a particular muscle group (myelinated advantageous in these situations)  The gaps between myelin sheath cells Nodes of Ranvier. The electrical impulse jumps from one node to the next in 120 m/s. This is called saltatory conduction.  large diameter nerve fibres conduct impulses faster than smaller diameter fibres but are harder to activate  in large muscle groups that generate large forces – they will have much larger nerve fibers innervating those muscle  require more activation and stimulus to activate the fibers  myelin sheaths insulate the nerve from the surrounding enviro – won’t lose charge  surrounding enviro is water – water conducts electricity – can lose impulse to the water Synapses - interface btwn nerve fiber and the subsequent nerve itself – communication btwn cell bodies - a synapse carries information from one nerve to another - the information may be inhibitory or excitatory - summed effect of inputs determines whether or not an action potential occurs - spatial or temporal summation - from one nerve to another or from nerve to muscle tissue 5 - inhibitory or excitatory – turn muscle on or off - specialized junctions cells of the nervous system signal to each other and to non-nerve cells such as those in muscles or glands. - depending on the input to the cell will dictate spatial or temporal stimulation Temporal and Spatial Summation Temporal = several impulses from one neuron over time - increased freq of stimulus down the same nerve - from brain, compliments reflexive stimuli Spatial = impulses from several neurons at the same time - sent down the same nerve – when you play a sport for a long time actions become reflexive, don’t have to think about your motions, become automatic – they are spinal cord reflexes so don’t have to use much of your brain to elicit actions - can complement the reflexive neurons output – input from the brain that will initiate the required movement – especially when sports are at high speeds – don’t have time to think about that you need to do Myocardium - even though myocardium has stimulus from sympathetic and parasympathetic it can prop the stimulus through the heart - myocardium will spontaneously depolarize and then transport it to diff areas of the heart through gap junctions Neuromuscular Junction - impulses from one fiber innervating a number of muscle fibers within the cell itself - one nerve innervates many muscle fibers through intramuscular junctions Transmission of Nerve Impulse at the Neuromuscular Junction - instead of sodium channels – at the NM junction the AP arrives – voltage gated channels specific to calcium - as it enters the pre synaptic terminal – vesicles contain acetylcholine – calcium causes release of acetyl from vesicles as the AP arrives - release of acetyl into pre-synaptic cleft - then sodium channels (not voltage gated) as specific receptors to acetyl - acetyl binds to receptors on channels and allows it to enter the muscle mem then the mem is depolarized 6 - surface of the muscle has the ability to depolarize and prop the AP - acetyl extrase enzyme -splits acetyl, choline is reabsorbed and binds with acetic acid then stored as acetylcholine until the next AP is received - outside mem of muscle = sarcolemma membrane Transmission of Nerve Impulse Intracellular Tubule System Transverse Tubule System   to myofibrils  partial function is spreading action potential depolarization from outer regions to deep areas  travels the length of the membrane down the T tubules (surrounding the indiv muscle fibers) allows entry of AP within the muscle itself (all areas of the muscle)  then travels down the sarcoplasmic reticulum which leads to the release of calcium – baths muscle fiber in calcium  communicates nervous impulses from T tubules to sarcoplasmic reticulum to elicit contraction Sarcoplasmic Reticulum  extensive network of tubular channels. To myofibrils  each tubule terminates in a saclike vesicle that stores Ca+  depolarization  release of Ca+  activates actin filaments  Ca stored in SR  Release of Ca leads to contraction  Contraction will occur until calcium is reabsorbed back up into the SR  In fatigue – as the ph changes calcium release is inhibited and calcium uptake is also inhibited = tetanus – muscle isn’t contracting or relaxing 7 Lecture 3 Spinal Cord Injuries - Spinal cord injuries and the effects of the location of the injury on function - Higher in spinal cord the greater limited dysfunction you are going to see - High disruption – lose all limb function (can still, think, see breathe) - Thoracic legion – will have full function above that area, limited below, Lumbar legion, Coccyx – little bit of dysfunction in the leg - The SR functions to uptake calcium from the sarcoplasm and to release calcium into the sarcoplasm to initiate contraction and sequester it during relaxation. - Down T tubules – connected to SR where calcium is stored - Ca released as the action potential travels through the T tubules – Ca leads to the contrsction of the muscle itself - Contraction will continue to occur as long as there is calcium - When it is reabsorbed contraction stops What happens when calcium is released from the SR? - 3 main sources of ATP used, ATP used in calcium ATPase pump to end contraction Triad - On both sides of a T-tubule are dilated end sacs of the sarcoplasmic reticulum called the terminal cisternae. A T-tubule, together with its two terminal cisternae, is called a muscle triad. 8 Sliding Filament Theory - Movement of actin and myosin to shorten the muscle - Z- line with sarcomere on either side - Z line = anchor point - H -zone = distance btwn the actin on either side of the sarcomere (actin bond to the z line on either side of the myosin)during contraction the H- zone will disappear as the actin moves towards each other - Middle z line will stay the same as everything moves towards the middle – contraction on both sides - I band will get smaller - A- band = outer edges of the myosin, will not change - Myosin length itself doesn’t change, Sliding that shortens the sarcomere - Pulling from both directions – pulling on the origin and insertion - Sarcomere being pulled to the z line - Interaction btwn the actin and myosin - Myosin heads are swiveling and pushing actin towards each other - 10,000 of sarcomeres working together to shorten the muscle Myosin -Actin Interaction - Actin , Tropomyosin wound around actin, Troponin - Calcium binds to troponin which is attached to tropomyosin - Mysoin binding sites are underneath the tropomyosin - Binding sites are unmasked/moved so the mysoin heads can bind to the actin so that contraction can occur - Magnesium ion activates Myosin head causing release of Phosphorus ion from ATP leaving ADP and causing the Myosin head to contract. - ATP will bond to myosin head – this binding causes the release of the myosin head from the actin (after the myosin head has swiveled after contraction) - Magnesium – what activates ATP hydrolysis (breakdown of ATP) when it binds to the myosin head – when energy is released from splitting of ATP then the filaments actually move and the contraction occurs 9 Link between Actin, myosin and ATP  energy is provided for x-bridge movement when P split from ATP.  detachment of myosin X-bridges from actin filament occurs when ATP joined to Actomysosin complex  returns to original state Key enzyme: myosin ATPase , splits ATP making energy available for contraction. - Slow twitch and fast twitch determined by the amt of this enzyme – more means that energy will be released faster and therefore the muscle can contract faster and generate more torque - Enzyme determines twitch characteristics Summary Actin and Myosin proteins - myosin is the thick filament to which myosin heads are attached -troponin and tropomyosin part of the actin these regulate contact between filaments during contraction troponin -affinity to Ca+, Ca+ and troponin triggers myofibrils to interact and slide past each other (Mg activates myosin-ATP hydrolysis) tropomyosin- prevents premature coupling of actin/myosin sarcomere: repeating unit between two z lines. Functional unit of the cell Important Contractile Properties Length – tension relationship  there is an optimal length for maximum force production - Optimal length of the muscle for it to generate the greatest amt of force – means that there will be certain angles around joints and particular movements that enable you to generate more force and angles that allow you to generate less force - Long length is a very weak position (elbow fully extended, knees fully flexed) - Stay away from angles that generate the least force - Also very weak when the muscle is fully shortened – generate very little force - Stay away from limb angles that lead to length or shortening of the muscle, Small range where it can generate maximal force - What angels does the muscle generate the greatest amt of force – applied to the sport being played - when you have completely lengthened muscle you will have the fewest cross bridges being made(more crossbridges=more force) - When doing bicep curl it is hard to start the movement b/c muscle is fully lengthened - When the muscle is fully contracted all the crossbridges that can be made have been made so you cant generate anymore force - 120degrees is when you can generate the most force - All muscle groups in a similar fashion - Mid range is the most powerful, full flexion or full extension is weaker - In sport when you are trying to move ppl around – better when you are in optimal position 10 Force –Velocity Relationship  highest force is generated at slowest velocity 1. Increased Velocity: dec time for x-bridge formation , less force 2. Greater force : Need to recruit more fibres and x bridges 3. greater force: fiber shortening times are longer - Angle that the muscle is at will dictate the force being generated - Power (force per unit time) is important - Isometric contraction (no change in length) - a lot of force can be generated, as soon as the muscle starts to shorten and the faster it shortens the less force you are going to be able to generate - Can generate a lot of force if you go slowly - Trade off btwn force and velocity - Slower the movement the more crossbridges you are able to make - It takes time to make crossbridges – as the muscle shortens faster and faster less time to make crossbridges - Move faster cant generate as much force b/c less cross bridges - Velocity of shortening - High velocity = low force, High force = low velocity - Speed of movement and when you generate the greatest amt of power - At mid velocity when you can generate the most power (power = force x distance (work)/ time) - More powerful you are doing work in shorter period of time and in mid range velocity - Diff velocities capable in diff fiber types - Slow fiber types have slow contracting velocity – related to amt of myosin ATPase in the muscle - Discus  throwers are big, with increase velocity means less crossbridges o If you are huge then you will have a lot of crossbridges – a lot of contractile proteins o Even though he is only using some of them he has so many more that he can generate a lot more power o In power sports it is good to be big b/c can generate more cross bridges Types Of Muscle Contraction Isotonic = constant resistance (dynamic) - Keeping the force the same as you go through the motion Isometric – constant length (static) - Happens a lot in contact sports where you are pushing against an indiv – no change in length of muscle Isokinetic = constant speed, changing load - Machine will always move the same speed, when you go through full range of motion – helpful for rehab - When running down a hill – breaking motion, muscle is being lengthened Eccentric = lengthening contraction - Very strong contractions compared to concentric - Sports where you are trying to move ppl (eccentric) way stronger than the person pushing you forward, stronger when you are working eccentrically than when you are working concentrically Concentric = shortening contraction 11 Lecture 4 Divers - Tape wrists – the impact of hitting the water - need to maintain body positions as they are spinning and somersaulting - have to be very compact, requires a lot of strength to work against the centripetal force Concentric Contractions - Concentric contractions at high velocity and then slower contraction – 0 is an isometric contraction - As it continues into eccentric it is a lengthening contraction – increasing speed of lengthening contraction - Concentric contraction = low forces - Faster and faster lengthening contraction the force will increase - Can generate more force eccentrically - As you decelerate it will be an eccentric contraction - Smaller person will be very effective if they are pushed slowly backwards – generate more force Motor Units  motor nerve and all the muscle fibres innervated by it  may be spread throughout muscle  all fibres within a given motor unit share the same characteristics  Diff btwn man and animal – animal have homogoneous muscle groups – man has slow twitch and fast twitch  Can have very large motor units  Fibers will have the same metabolic characteristics – all going to be slow or fast twitch, have the same glycolytic capacity and aerobic capacity  motor units are of different sizes and allow graded contraction  sizes differ due to fibre size and number  can have a mixture of diff fiber types and motor units within the same muscle matrix  recruited from smallest to largest  fibers in same motor unit: same enzymatic profile and same twitch characteristics 12 Motor Units within Fibre Types - Many fibers - Stimulated a single nerve to determine the size of the motor unit – how many fibers associated with a particular nerve - Stimulate the nerve for a number of minutes until all the glycogen in the fibers have been used - Determine for that particular nerve – the white fibers are depleted of glycogen – all of these fibers are depleted of glycogen Motor Unit (glycogen depletion method) - One motro unit has 385 fibers - FR = Fatigue resistant – same as FOG - FF same as FT - S same as ST - In the slow twitch fibers there is a smaller number associated with a particular nerve Wave Summation - Electrical stimulation experiments - Twitch develops as you increase force – initially as the contraction occurs the force is being generated very quickly - The length of time of the relaxation is much longer – takes longer for the muscle to relax/lengthen than it does to shorten - As the muscle becomes fatigue it is more difficult for it to contract and shorten - Muscle doesn’t lengthen as quickly - If you continue to increase the length of stimulation, if the duration btwn one stimulus and the next stimulus – summation of force - Muscles doesn’t have time to completely relax – the next stimulation comes along before that particular twitch has fully relaxed - starting to recruit more fibers - Cumulative force as the frequency of stimulation continues to increase – if the stimulation is really high then there is no relaxation = tetanus 13 Motor Unit Recruitment Pattern  motor units exhibit an all-or-none response  increased rate of stimulation leads to tetany  wave summation All or none response  single nerve being innervated – either going to get all the fibers stimulating the muscle or none at all  Cant change the number of fibers within a motor unit being stimulated Power, Frequency and Aging Absolute Max power vs. Stimulation frequency - Max power generated related to freq - Does the max power of specific muscle groups change with age - Max power generated at any given freq – there are differences btwn young group and adult group and the adult group and older groups - Adult group can generate more absolute power - Young and old were the same Relative Max Power vs. Stimulation Frequency - As you increase freq of stimulation how does stimulation change relative to each groups max power - No statistical significance btwn adult and young averages - Relative to each groups max power there isn’t any diff in age – can still generate 75% of absolute power particular freq Muscle Fiber Types - Muscle biopsy – have the person contract muscle and when they relax a small piece of the muscle tissue is snipped off, put into a slicer and get serial sections to determine the diff fiber types and their characteristics - 2 broad categories: o Fast-twitch (FT) o Slow-twitch (ST)  FT can easily be subdivided into subgroups 14 Myosin ATPase - Stain the fibers to determine diff properties of fibers - If a particular fiber has a lot of myosinATPase it will come out as a dark stain - Dark fibers have a lot of mypsin ATPase - Fiber number 2 – fast twitch - 4 and 6 are slow twitch - All the chemicals in the muscle are preserved – put in liquid nitrogen after it is extracted NADH - The more NADH you have in a fiber means you have more substrate to go the the electron transport chain - More NADH the more ATP you can release - Number 2 is stained for NADH – very low levels of NADH - If it is high in myosin ATPase it will not have a high aerobic capacity - Fibers that were low in myosin ATPase have high amts of NADH – aerobic metabolism – NADH is substrate - With weight lifters – 50/50 ST to FT - ST can generate a lot of force just not very quickly Muscle Capillarity - Blood flow – transport of oxygen - Oxidative fibers are darker - Black dots surrounding fibers are capillaries – 4-5 capillaries around each of the fibers (left - Right pic – fast twitch fibers are light colored fast twitch fibers have low capilarization and low blood flow 15 Lecture 5 Body Builders - To get rid of subcutaneous fat – last few days before competition have to work to deplete glycogen to get rid of water and get more definition Muscle Size and Power - Diff in muscle size relative to the number of contractions required in the performance - Weight lifters – one large contraction – they have large muscles - Usain bolt – 31 contractions for 100 meter dash – smaller muscle size, requires less hypertrophy in the legs, but they have relatively large upper body so that they can be more powerful in the beginning of the race - 400 m runner – they have smaller upper body and legs - requires minimal strength but a lot of aerobic power Fiber Types and Increasing Force - Contribution of force to the total force being generated in the movement - ST fibers do generate significant amt of force – 60% of force generated by slow twitch fibers - Fast twitch can generate 20% more force - Force is a cumulative effect of all three fiber types Muscle Fibre Characteristics - Type 2b and types 2 x/d – diff b/c the 2b fibers are found in mammals - a greater anaerobic component relative to the 2x fibers - 2x fibers are the equivalent 2b fibers in humans but they are not as glycolytic as the 2b found in animals, MUSSCLLEFIBRRE CHAARACCTERRSTTCSS 2x fibers are more oxidative Name Type I Type IIa Type IIb
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