Oxidative Metabolism in Cardiac Muscle
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Questions and Answers

What is the enzyme responsible for phosphorylating creatine in the muscle?

  • Creatine synthase
  • Creatine phosphatase
  • Creatine kinase
  • Creatine phosphokinase (correct)

    • What is the source of energy that reconstitutes the ATP molecule?

  • Fermentation
  • Glycolysis
  • Phosphocreatine (correct)
  • Oxidative metabolism

    • What is the byproduct of glycolysis that accumulates in the muscle?

  • Pyruvate
  • Glucose
  • Lactate (correct)
  • Alanine

    • What is the rate of ATP formation by glycolysis compared to oxidative metabolism?

    <p>2.5 times faster</p> Signup and view all the answers

    What is the purpose of phosphocreatine in muscle contraction?

    <p>To regenerate ATP quickly</p> Signup and view all the answers

    Where is creatine produced from amino acids?

    <p>Liver</p> Signup and view all the answers

    What is the characteristic of glycolysis that allows muscle contraction to be sustained without oxygen delivery from the blood?

    <p>It is an anaerobic process</p> Signup and view all the answers

    What is the purpose of glycolysis in the muscle?

    <p>To release energy and produce pyruvic acid and lactic acid</p> Signup and view all the answers

    What occurs when the frequency of muscle contractions reaches a critical level?

    <p>The successive contractions fuse together</p> Signup and view all the answers

    What is the ideal length for a skeletal muscle to operate with the greatest active tension?

    <p>When the muscle is close to its resting length</p> Signup and view all the answers

    What happens when the frequency of muscle contractions increases?

    <p>The strength of contraction rises progressively</p> Signup and view all the answers

    What is the term for a contraction of maximal strength where successive contractions fuse together?

    <p>Tetanization</p> Signup and view all the answers

    What determines the amount of tension generated during a muscle contraction?

    <p>The number of cross-bridge interactions</p> Signup and view all the answers

    What happens to the muscle contraction strength when the muscle is shortened or stretched?

    <p>It diminishes</p> Signup and view all the answers

    What is the relationship between the length of a muscle before contraction and the tension it can develop?

    <p>Length-tension relationship</p> Signup and view all the answers

    What happens when a muscle fiber is stimulated rapidly?

    <p>It does not have a chance to relax at all</p> Signup and view all the answers

    What percentage of energy used for contraction is attributed to oxidative metabolism?

    <p>95%</p> Signup and view all the answers

    What is the primary source of energy for cardiac muscle?

    <p>Fatty acids</p> Signup and view all the answers

    What is the percentage of cytoplasm volume occupied by mitochondria in cardiac fibers?

    <p>40%</p> Signup and view all the answers

    What is the storage form of fatty acids in cardiac muscle?

    <p>Lipid droplets</p> Signup and view all the answers

    What is the approximate percentage of energy that comes from glucose and lactate in cardiac muscle?

    <p>10-30%</p> Signup and view all the answers

    What happens to cardiac cells after 30 seconds of O2 deprivation?

    <p>They stop contracting</p> Signup and view all the answers

    For what duration can cardiac muscle rely on carbohydrates for energy?

    <p>Short periods</p> Signup and view all the answers

    What is the percentage of skeletal muscle fibers occupied by mitochondria?

    <p>2%</p> Signup and view all the answers

    What determines the number of cross-bridge interactions in a muscle?

    <p>The degree of overlap between thick and thin filaments</p> Signup and view all the answers

    What is the optimal condition for muscle contraction?

    <p>When the muscle is at its optimal resting length</p> Signup and view all the answers

    What occurs when a muscle is too shortened?

    <p>Muscle contraction cannot progress</p> Signup and view all the answers

    What is the primary function of the calcium pump in the SR?

    <p>To remove calcium ions from the cytosol</p> Signup and view all the answers

    What is the purpose of rephosphorylation of ADP in muscle tissue?

    <p>To allow contraction to continue</p> Signup and view all the answers

    What are the three sources of energy for muscle contraction?

    <p>ATP, glycolysis, and oxidative phosphorylation</p> Signup and view all the answers

    What is the type of response seen in muscle fibers when exposed to a threshold stimulus?

    <p>All-or-none response</p> Signup and view all the answers

    What determines the strength of contraction in the body?

    <p>The number of motor units recruited and the frequency of stimulation</p> Signup and view all the answers

    What is the result of muscle contraction when the sarcomere is in the optimal resting length?

    <p>Maximal tension is achieved</p> Signup and view all the answers

    What is the term for the time between a stimulus to the motor neuron and the subsequent contraction of the innervated muscle?

    <p>Latent period</p> Signup and view all the answers

    What is the consequence of limited ATP in muscle tissue?

    <p>Rephosphorylation of ADP must occur</p> Signup and view all the answers

    What occurs when another action potential comes before the complete relaxation of a muscle twitch?

    <p>Summation</p> Signup and view all the answers

    What is the term for a single contraction and relaxation cycle produced by an action potential within the muscle fiber itself?

    <p>Twitch</p> Signup and view all the answers

    What is the type of summation that occurs when the number of motor units recruited increases?

    <p>Multiple fiber summation</p> Signup and view all the answers

    What is the term for the state of muscle contraction where the muscle contracts at a maximum frequency?

    <p>Tetanus</p> Signup and view all the answers

    What is the characteristic of muscle contraction that is controlled in the body by changing the number of motor units recruited and/or the frequency of stimulation?

    <p>Strength of contraction</p> Signup and view all the answers

    Study Notes

    Oxidative Metabolism

    • Responsible for 95% of energy used for contraction
    • Combines O2 with end products of glycolysis (e.g. lactate) and other energy sources (proteins, lipids, carbohydrates) to produce ATP
    • Main energy source for cardiac muscle, derived from oxidative metabolism of fatty acids
    • Mitochondria make up 40% of cytoplasm volume in cardiac fibers (compared to 2% in skeletal muscle fibers)
    • Numerous lipid droplets containing triglycerides (storage form of fatty acids) found in cardiac muscle
    • Only 10-30% of energy comes from glucose and lactate; glycogen granules are found in cardiac muscle
    • Cardiac cells stop contracting after 30 seconds of O2 deprivation

    Phosphocreatine (Creatine Phosphate)

    • Creatine produced from amino acids in liver, phosphorylated in muscle by enzyme creatine phosphokinase to produce phosphocreatine
    • Carries high-energy phosphate bond similar to ATP bonds
    • Used to reconstitute ATP molecule; cleavage of phosphocreatine releases energy used to bond new phosphate ion to ADP to reconstitute ATP
    • Small amount of phosphocreatine found in muscle

    Glycolysis

    • Enzymatic breakdown of carbohydrates (glucose and glycogen) to produce pyruvic acid and lactic acid, releasing energy
    • Energy used to reconstitute both ATP and phosphocreatine
    • Can occur in absence of oxygen; muscle contraction can be sustained for over a minute without O2 delivery from blood
    • Rate of ATP formation by glycolysis is 2.5 times faster than ATP formation by oxidative metabolism
    • Many end products accumulate, including lactate

    Muscle Physiology

    Muscle Strength and Length-Tension Relationship

    • Muscle contraction strength controlled by changing number of motor units recruited and/or frequency of stimulation
    • All-or-none response: muscle fiber contracts maximally or not at all
    • Strength of contraction can be separated into twitch, summation, and tetanus
    • Twitch: single contraction and relaxation cycle produced by action potential within muscle fiber
    • Summation: occurs in two ways: multiple fiber summation (increased number of motor units recruited) and frequency summation (increased frequency of stimulation)
    • Tetanus: contraction of maximal strength resulting from rapid successive contractions
    • Latent period: time between stimulus to motor neuron and subsequent contraction of innervated muscle

    Length-Tension Relationship

    • Skeletal muscles operate with greatest active tension when close to ideal length (often resting length)
    • Length-tension relationship: relation between length of muscle before contraction and tension generated during contraction
    • Optimal length for maximal force generation varies for each muscle
    • Muscle fibers can contract forcefully when stimulated over a relatively narrow range of resting lengths

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    Muscle Physiology Lecture Notes PDF

    Description

    This quiz covers the process of oxidative metabolism in cardiac muscle, including the sources of energy and the production of ATP.

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