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outline 12
Comparative Physiology- Renner Lecture 12
| Question | Answer |
|---|---|
| what are two significant roles of Ca2+ in muscle contraction? | 1. induction of conformational change in troponin by binding to C-site-move tropomyosin inward between the 2 F actins exposing binding sites on G-actin 2. Cofactor for ATPase associated with lighter myosin strand in the myosin head |
| what regulates Ca2+ levels? | sarcoplasmic reticulum which has glycogen granules as well as Ca2+ |
| what are some functions of the sarcoplasmic reticulum? | 1. Ca2+ storage, release and reabsorption 2. major site of glycolysis |
| considering the structure of the sarcoplasmic reticulum, what structures refer to flattened discs of sarcoplasmic reticulum found in I zones near the z line | Terminal cisternae |
| considering the structure of the sarcoplasmic reticulum, what structures are found in the center region of sarcomere? | H-sacs |
| considering the structure of the sarcoplasmic reticulum, what structures form connecting elements between the terminal cisternae and H-sacs? | Longitudinal elements |
| considering the structure of the sarcoplasmic reticulum, what are the invaginations of sarcolemma found in Z line region? | Transverse tubule |
| what are functions of transverse or T tubules? | 1. open- in contact with ECF 2. branch to interface with multiple myofibrils 3. carry AP rapidly deep into the muscle |
| when ap happens these structures carry impulse deep into the muscle | t-tubules |
| _________________ are four subunits on t tubules that block four subunits of a receptor called ______________ on the terminal cisternae when the muscle is at rest | dihydropyridine receptors, ryanodine recetors |
| dihydropyridine receptors are on the ___________________ and ryanodine recetors are on the ______________________ | t tubules, terminal cisternae |
| subunits of ryanodine receptors are ______________ | calcium channels |
| what block dihydropyridine receptors? | drug called dihydropyridine |
| dihydropyridine receptors block ryanodine receptors at rest but when depolarization happens, dihydropyridine receptors move to open ryanodine receptors which act as ___________________ encouraging its diffusion from the ____________ to the ______________ | calcium channels, sarcoplasmic reticulum, sarcoplasm |
| the opening of ryanodine receptors _________________ permeability of SR membrane for Ca2+, and since it is available in high concentrations there, it will __________________ into the __________________ | increases, diffuse, sarcoplasm |
| the opening of ryanodine receptors increases Ca2+ concentration in sarcoplasm by ____________ and that entire process takes about ___________sec | 500 times, 0.05 |
| what relaxes the muscle? | removal of Ca2+ from the sarcoplasm, Sarcoplasmic reticulum Ca2+ ATPase pump transports Ca2+ back into sarcoplasmic reticulum |
| what is the function of calsequestrin? | protein in SR can store about 40 Ca2+ ions |
| Ca2+ concentration in the SR is __________times that in the sarcoplasm when the muscle at rest | 10,000 |
| if ATP synthesis were blocked in vertebrates, what other alternative is there? | phosphocreatine, 5x higher concentration of ATP, it also contains kinase. Phosphocreatine+ADP----(creatine/kinase)--> creatine+ATP |
| as phosphocreatine is depleted, what happens? | concentration of ATP is decreased, ADP is increased ADP+ADP----(myokinase)--> ATP+ANP (take one Pi give it to other) |
| what is a motor unit | a motor neuron and the muscle fibers it innervates |
| size of motor units? | varies. 1. gastrocnemius: 1motor neuron-innervates 1700 muscle fibers 2. eye: 1 motor neuron-innervates 7 muscle fibers |
| what does the tension generated by a contraction depend on? | 1. active component- overlap between actin&myosin. Cross bridge formation 2. passive component- parallel: connective tissue lining sarcolemma+muscle, series: tendons, ligaments; muscle to joints |
| as the muscle is stretched, tension ______________, until it reaches a/an _____________________ which means that maximal number of cross bridges is formed. Then finally, active tension drops | increases, optimal length |
| what is supramaximal stimulus? | signal voltage that is strong enough to activate all motor units in a muscle |
| what does lower tension cause? | partial overlap of actin-myosin fibers. interfaces w cross bridge formation |
| what are the two elastic elements of the muscle? | parallel elastic: sarcolemma, connective tissue series elastic: tendons, aponeurosis |
| what are two types of tension generated by a muscle? | isometric or isotonic |
| what is the difference between isometric and isotonic contractions? | 1. isometric- muscle does not shorten during contraction. series elastic stretch(tendons) 2. isotonic- muscle shortens to lift load, passive tension decreases. Slight change in series component to assume some load |
| TRUE/FALSE: most contractions are only isotonic | FALSE. they are a combination of isometric and isotonic |
| consider running, how do isometric and isotonic components work together? | isotonic- movement of legs isometric- quads tightening at knee joints |
| for muscles, how is tension altered? | by altering the number of motor neurons activated, allowing for gradation of movement |
| what happens when stimulus intensity is increased? | recruit more motor units to increase tension, fibers and associated neurons have different thresholds |
| minimum voltage or stimulus intensity required to activate all of the motor units | maximal voltage |
| the effect where a series of stimulations result in a series of corresponding contractions that increases in amplitude until it reaches a steady state. stimulus is fixed | treppe |
| from resting state, initial muscle contraction strength in response to the first stimulus may only be _________of peak muscle performance | 50% |
| what two factors contribute to treppe? | 1. tension from actin-myosin interaction in response to first stimulation is applied to overcome series elastic component 2. increased Ca2+ in sarcoplasm from series of contractions |
| when frequency is increased and tension is measured. Tension keeps increasing at first then the ferquency is rapid enough that the muscle contraction strength reaches maximum value and no relaxation happens because Ca2+ remains high in the sarcoplasm | tetanic contraction |
| tetanization is_______________ | maximal sustained contration |
| what causes muscle cramps | hyper-excitability of motor neurons |
| if next stimulus is delivered before Ca2+ is cleared from the sarcoplasm, summation can lead to ____________ | tetanic contraction |
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rusulali97
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