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Questions and Answers
What is the enzyme responsible for phosphorylating creatine in the muscle?
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?
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?
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?
What is the rate of ATP formation by glycolysis compared to oxidative metabolism?
What is the purpose of phosphocreatine in muscle contraction?
What is the purpose of phosphocreatine in muscle contraction?
Where is creatine produced from amino acids?
Where is creatine produced from amino acids?
What is the characteristic of glycolysis that allows muscle contraction to be sustained without oxygen delivery from the blood?
What is the characteristic of glycolysis that allows muscle contraction to be sustained without oxygen delivery from the blood?
What is the purpose of glycolysis in the muscle?
What is the purpose of glycolysis in the muscle?
What occurs when the frequency of muscle contractions reaches a critical level?
What occurs when the frequency of muscle contractions reaches a critical level?
What is the ideal length for a skeletal muscle to operate with the greatest active tension?
What is the ideal length for a skeletal muscle to operate with the greatest active tension?
What happens when the frequency of muscle contractions increases?
What happens when the frequency of muscle contractions increases?
What is the term for a contraction of maximal strength where successive contractions fuse together?
What is the term for a contraction of maximal strength where successive contractions fuse together?
What determines the amount of tension generated during a muscle contraction?
What determines the amount of tension generated during a muscle contraction?
What happens to the muscle contraction strength when the muscle is shortened or stretched?
What happens to the muscle contraction strength when the muscle is shortened or stretched?
What is the relationship between the length of a muscle before contraction and the tension it can develop?
What is the relationship between the length of a muscle before contraction and the tension it can develop?
What happens when a muscle fiber is stimulated rapidly?
What happens when a muscle fiber is stimulated rapidly?
What percentage of energy used for contraction is attributed to oxidative metabolism?
What percentage of energy used for contraction is attributed to oxidative metabolism?
What is the primary source of energy for cardiac muscle?
What is the primary source of energy for cardiac muscle?
What is the percentage of cytoplasm volume occupied by mitochondria in cardiac fibers?
What is the percentage of cytoplasm volume occupied by mitochondria in cardiac fibers?
What is the storage form of fatty acids in cardiac muscle?
What is the storage form of fatty acids in cardiac muscle?
What is the approximate percentage of energy that comes from glucose and lactate in cardiac muscle?
What is the approximate percentage of energy that comes from glucose and lactate in cardiac muscle?
What happens to cardiac cells after 30 seconds of O2 deprivation?
What happens to cardiac cells after 30 seconds of O2 deprivation?
For what duration can cardiac muscle rely on carbohydrates for energy?
For what duration can cardiac muscle rely on carbohydrates for energy?
What is the percentage of skeletal muscle fibers occupied by mitochondria?
What is the percentage of skeletal muscle fibers occupied by mitochondria?
What determines the number of cross-bridge interactions in a muscle?
What determines the number of cross-bridge interactions in a muscle?
What is the optimal condition for muscle contraction?
What is the optimal condition for muscle contraction?
What occurs when a muscle is too shortened?
What occurs when a muscle is too shortened?
What is the primary function of the calcium pump in the SR?
What is the primary function of the calcium pump in the SR?
What is the purpose of rephosphorylation of ADP in muscle tissue?
What is the purpose of rephosphorylation of ADP in muscle tissue?
What are the three sources of energy for muscle contraction?
What are the three sources of energy for muscle contraction?
What is the type of response seen in muscle fibers when exposed to a threshold stimulus?
What is the type of response seen in muscle fibers when exposed to a threshold stimulus?
What determines the strength of contraction in the body?
What determines the strength of contraction in the body?
What is the result of muscle contraction when the sarcomere is in the optimal resting length?
What is the result of muscle contraction when the sarcomere is in the optimal resting length?
What is the term for the time between a stimulus to the motor neuron and the subsequent contraction of the innervated muscle?
What is the term for the time between a stimulus to the motor neuron and the subsequent contraction of the innervated muscle?
What is the consequence of limited ATP in muscle tissue?
What is the consequence of limited ATP in muscle tissue?
What occurs when another action potential comes before the complete relaxation of a muscle twitch?
What occurs when another action potential comes before the complete relaxation of a muscle twitch?
What is the term for a single contraction and relaxation cycle produced by an action potential within the muscle fiber itself?
What is the term for a single contraction and relaxation cycle produced by an action potential within the muscle fiber itself?
What is the type of summation that occurs when the number of motor units recruited increases?
What is the type of summation that occurs when the number of motor units recruited increases?
What is the term for the state of muscle contraction where the muscle contracts at a maximum frequency?
What is the term for the state of muscle contraction where the muscle contracts at a maximum frequency?
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?
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?
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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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