Podcast
Questions and Answers
Which of the following scenarios would most likely involve the predominant use of fast glycolytic (Type IIb) muscle fibers?
Which of the following scenarios would most likely involve the predominant use of fast glycolytic (Type IIb) muscle fibers?
- A cyclist riding at a moderate intensity for an extended period.
- A marathon runner maintaining a steady pace for several hours.
- A weightlifter performing a single, maximal lift. (correct)
- A yoga instructor holding a static pose for several minutes.
Smooth muscle contraction relies on troponin to initiate cross-bridge formation, similar to skeletal muscle contraction.
Smooth muscle contraction relies on troponin to initiate cross-bridge formation, similar to skeletal muscle contraction.
False (B)
Explain how the absence of ATP would prevent muscle relaxation, even if calcium ions were actively being pumped back into the sarcoplasmic reticulum.
Explain how the absence of ATP would prevent muscle relaxation, even if calcium ions were actively being pumped back into the sarcoplasmic reticulum.
ATP is required for the detachment of myosin from actin. Without ATP, the cross-bridges remain bound, preventing relaxation.
In smooth muscle, calcium ions bind to ______, leading to the activation of a kinase enzyme that initiates muscle contraction.
In smooth muscle, calcium ions bind to ______, leading to the activation of a kinase enzyme that initiates muscle contraction.
Match the muscle fiber type with its primary energy source during sustained activity:
Match the muscle fiber type with its primary energy source during sustained activity:
During muscle contraction, what is the direct role of ATP hydrolysis?
During muscle contraction, what is the direct role of ATP hydrolysis?
The A-band in a sarcomere decreases in length during muscle contraction as the actin filaments slide over the myosin filaments.
The A-band in a sarcomere decreases in length during muscle contraction as the actin filaments slide over the myosin filaments.
Explain why a buildup of lactic acid during intense exercise can lead to muscle fatigue.
Explain why a buildup of lactic acid during intense exercise can lead to muscle fatigue.
The ______ is the area within the sarcomere that contains only myosin filaments and is visible when the muscle is relaxed.
The ______ is the area within the sarcomere that contains only myosin filaments and is visible when the muscle is relaxed.
Match the following components of muscle tissue with their respective functions:
Match the following components of muscle tissue with their respective functions:
What would be the immediate consequence if the enzyme acetylcholinesterase were inhibited at the neuromuscular junction?
What would be the immediate consequence if the enzyme acetylcholinesterase were inhibited at the neuromuscular junction?
Cardiac muscle relies on external nerve stimulation for each contraction.
Cardiac muscle relies on external nerve stimulation for each contraction.
Describe the role of troponin and tropomyosin in preventing continuous muscle contraction when calcium levels are low.
Describe the role of troponin and tropomyosin in preventing continuous muscle contraction when calcium levels are low.
The process by which an action potential in the muscle fiber leads to the release of calcium ions from the sarcoplasmic reticulum is known as ______.
The process by which an action potential in the muscle fiber leads to the release of calcium ions from the sarcoplasmic reticulum is known as ______.
Match the type of muscle tissue with its unique structural feature:
Match the type of muscle tissue with its unique structural feature:
Why is the presence of ATP necessary for muscle relaxation?
Why is the presence of ATP necessary for muscle relaxation?
Increasing the frequency of motor neuron stimulation always results in complete tetanus, where the muscle achieves a state of maximal and sustained contraction with no relaxation.
Increasing the frequency of motor neuron stimulation always results in complete tetanus, where the muscle achieves a state of maximal and sustained contraction with no relaxation.
Explain why rigor mortis occurs after death in terms of ATP availability and muscle contraction.
Explain why rigor mortis occurs after death in terms of ATP availability and muscle contraction.
The neurotransmitter released at the neuromuscular junction that initiates muscle contraction is ______.
The neurotransmitter released at the neuromuscular junction that initiates muscle contraction is ______.
Match the type of muscle tissue with its primary function:
Match the type of muscle tissue with its primary function:
Which of the following events directly triggers the release of calcium ions from the sarcoplasmic reticulum in skeletal muscle?
Which of the following events directly triggers the release of calcium ions from the sarcoplasmic reticulum in skeletal muscle?
Smooth muscle cells have sarcomeres, which give them a striated appearance similar to skeletal and cardiac muscle.
Smooth muscle cells have sarcomeres, which give them a striated appearance similar to skeletal and cardiac muscle.
Explain how the length-tension relationship affects the force a muscle can generate.
Explain how the length-tension relationship affects the force a muscle can generate.
The regulatory protein that blocks myosin-binding sites on actin when calcium levels are low is ______.
The regulatory protein that blocks myosin-binding sites on actin when calcium levels are low is ______.
Match the zone/band of the sarcomere with its compositional change during muscle contraction:
Match the zone/band of the sarcomere with its compositional change during muscle contraction:
What is the function of the calcium ATPase pump in muscle relaxation?
What is the function of the calcium ATPase pump in muscle relaxation?
Increasing the number of activated motor units will decrease the force of muscle contraction.
Increasing the number of activated motor units will decrease the force of muscle contraction.
Describe how the arrangement of actin and myosin filaments within a sarcomere contributes to the striated appearance of skeletal muscle.
Describe how the arrangement of actin and myosin filaments within a sarcomere contributes to the striated appearance of skeletal muscle.
The connection between a motor neuron and a muscle fiber is called the ______.
The connection between a motor neuron and a muscle fiber is called the ______.
Match each muscle type with its type of control:
Match each muscle type with its type of control:
Which statement accurately describes the role of the Z-line in a sarcomere?
Which statement accurately describes the role of the Z-line in a sarcomere?
Smooth muscle fatigue occurs more rapidly than skeletal muscle fatigue due to its higher energy requirements.
Smooth muscle fatigue occurs more rapidly than skeletal muscle fatigue due to its higher energy requirements.
Explain how the sodium-potassium pump contributes to maintaining the resting membrane potential in muscle cells and its importance for muscle excitability.
Explain how the sodium-potassium pump contributes to maintaining the resting membrane potential in muscle cells and its importance for muscle excitability.
The ability of muscle tissue to return to its original length after stretching is known as ______.
The ability of muscle tissue to return to its original length after stretching is known as ______.
Match the term with its accurate definition related to muscle contraction.
Match the term with its accurate definition related to muscle contraction.
Which of these properties is NOT a characteristic that differentiates muscle tissue from other cell types?
Which of these properties is NOT a characteristic that differentiates muscle tissue from other cell types?
Skeletal muscles are primarily responsible for controlling the movement of internal organs and blood vessels?
Skeletal muscles are primarily responsible for controlling the movement of internal organs and blood vessels?
Within muscle tissue, what is the name given to the cytoplasm and the cell membrane, respectively?
Within muscle tissue, what is the name given to the cytoplasm and the cell membrane, respectively?
The functional unit of a muscle fibre responsible for contraction composed of actin and myosin proteins is called a ________
The functional unit of a muscle fibre responsible for contraction composed of actin and myosin proteins is called a ________
Match the muscle tissue types with their primary characteristics:
Match the muscle tissue types with their primary characteristics:
Which statement accurately describes the arrangement of contractile filaments within a sarcomere?
Which statement accurately describes the arrangement of contractile filaments within a sarcomere?
During muscle contraction, the length of both actin and myosin filaments decreases, resulting in the shortening of the sarcomere?
During muscle contraction, the length of both actin and myosin filaments decreases, resulting in the shortening of the sarcomere?
Explain the role of the myosin head in muscle contraction, including its binding sites and enzymatic activity.
Explain the role of the myosin head in muscle contraction, including its binding sites and enzymatic activity.
The energy required for the power stroke during muscle contraction is provided by the hydrolysis of _______, while the detachment of the myosin head from actin requires the binding of _______.
The energy required for the power stroke during muscle contraction is provided by the hydrolysis of _______, while the detachment of the myosin head from actin requires the binding of _______.
Match the following statements with whether they are associated with muscle tension or muscle load:
Match the following statements with whether they are associated with muscle tension or muscle load:
What is the primary function of the motor neuron in initiating muscle contraction?
What is the primary function of the motor neuron in initiating muscle contraction?
A single action potential in a motor neuron always results in a maximal, sustained contraction of all muscle fibres within its motor unit?
A single action potential in a motor neuron always results in a maximal, sustained contraction of all muscle fibres within its motor unit?
Describe the sequence of events at the neuromuscular junction that leads to muscle fibre depolarization.
Describe the sequence of events at the neuromuscular junction that leads to muscle fibre depolarization.
The enzyme __________ is responsible for breaking down acetylcholine in the synaptic cleft, which terminates the signal and allows the muscle fibre to relax
The enzyme __________ is responsible for breaking down acetylcholine in the synaptic cleft, which terminates the signal and allows the muscle fibre to relax
Each of the following descriptions lists a component of a muscle, match the component to its correct function:
Each of the following descriptions lists a component of a muscle, match the component to its correct function:
Which of the following correctly explains the role of tropomyosin and troponin in skeletal muscle contraction?
Which of the following correctly explains the role of tropomyosin and troponin in skeletal muscle contraction?
An increase in intracellular calcium levels always leads to muscle contraction regardless of the presence of ATP or the position of tropomyosin?
An increase in intracellular calcium levels always leads to muscle contraction regardless of the presence of ATP or the position of tropomyosin?
Explain the two distinct roles of ATP in muscle contraction.
Explain the two distinct roles of ATP in muscle contraction.
In excitation-contraction coupling, the action potential in the T-tubule membrane causes the DHP receptors to trigger the opening of __________ channels in the sarcoplasmic reticulum, leading to calcium release
In excitation-contraction coupling, the action potential in the T-tubule membrane causes the DHP receptors to trigger the opening of __________ channels in the sarcoplasmic reticulum, leading to calcium release
Match the following statements with whether they are associated with low or high cytosolic calcium, in relaxed or activated muscle:
Match the following statements with whether they are associated with low or high cytosolic calcium, in relaxed or activated muscle:
What happens during the latent period of muscle contraction?
What happens during the latent period of muscle contraction?
During concentric contraction, muscle tension is less than the load?
During concentric contraction, muscle tension is less than the load?
Describe the role of titin in the sarcomere and its impact on muscle function.
Describe the role of titin in the sarcomere and its impact on muscle function.
The A band of the sarcomere contains __________ filaments, while the I band contains __________ filaments.
The A band of the sarcomere contains __________ filaments, while the I band contains __________ filaments.
For each muscle fiber type, match its corresponding role:
For each muscle fiber type, match its corresponding role:
Which of the following best describes the function of the $Ca^{2+}$-ATPase pump in muscle relaxation?
Which of the following best describes the function of the $Ca^{2+}$-ATPase pump in muscle relaxation?
After death, rigor mortis occurs because the myosin heads are permanently bound to actin filaments due to the lack of ATP to unbind them?
After death, rigor mortis occurs because the myosin heads are permanently bound to actin filaments due to the lack of ATP to unbind them?
Briefly explain what role the Z-lines play in muscle contraction and relaxation.
Briefly explain what role the Z-lines play in muscle contraction and relaxation.
Motor neurons form specialized junctions with muscle fibres called __________, across which __________ is released to initiate muscle contraction.
Motor neurons form specialized junctions with muscle fibres called __________, across which __________ is released to initiate muscle contraction.
Match the type of muscle contraction wth the statement that best describes the scenario:
Match the type of muscle contraction wth the statement that best describes the scenario:
How does the frequency of action potentials in a motor neuron affect the force of muscle contraction?
How does the frequency of action potentials in a motor neuron affect the force of muscle contraction?
Smooth muscle cells are striated due to the highly regular arrangement of contractile filaments into sarcomeres?
Smooth muscle cells are striated due to the highly regular arrangement of contractile filaments into sarcomeres?
Describe the role of troponin in the mechanism of muscle contraction, including calcium binding and conformational changes.
Describe the role of troponin in the mechanism of muscle contraction, including calcium binding and conformational changes.
Changes in ______ ______ in the skeletal muscle cell will determine the number of cross-bridges that form, directly affecting the force of muscle contraction.
Changes in ______ ______ in the skeletal muscle cell will determine the number of cross-bridges that form, directly affecting the force of muscle contraction.
Match the definitions to the corresponding type of filaments present in a sacromere:
Match the definitions to the corresponding type of filaments present in a sacromere:
Which of the following structural changes occurs within the sarcomere during muscle contraction, supporting the sliding filament theory?
Which of the following structural changes occurs within the sarcomere during muscle contraction, supporting the sliding filament theory?
Muscle tension refers to the passive resistance of a muscle to stretching, while load is the force generated by the muscle contraction?
Muscle tension refers to the passive resistance of a muscle to stretching, while load is the force generated by the muscle contraction?
Describe the role of the transverse tubules (T-tubules) in excitation-contraction coupling within skeletal muscle fibres.
Describe the role of the transverse tubules (T-tubules) in excitation-contraction coupling within skeletal muscle fibres.
The process of excitation-contraction coupling relies on an ______ ______ that depolarizes the motor endplate in the muscle fibre
The process of excitation-contraction coupling relies on an ______ ______ that depolarizes the motor endplate in the muscle fibre
Match each of following terms with a function:
Match each of following terms with a function:
Which statement best describes the primary role of ATP in muscle contraction?
Which statement best describes the primary role of ATP in muscle contraction?
The shortening of myosin during muscle contraction primarily drives the sliding filament theory.
The shortening of myosin during muscle contraction primarily drives the sliding filament theory.
Describe the critical event initiated by the action potential that directly leads to the release of Calcium ions ($Ca^{2+}$) from the sarcoplasmic reticulum.
Describe the critical event initiated by the action potential that directly leads to the release of Calcium ions ($Ca^{2+}$) from the sarcoplasmic reticulum.
The ______ is defined as the force created by a contracting muscle, while the ______ is the weight or force that opposes muscle contraction.
The ______ is defined as the force created by a contracting muscle, while the ______ is the weight or force that opposes muscle contraction.
Which of the following statements accurately describes the structural arrangement within a sarcomere during muscle contraction, according to the sliding filament theory?
Which of the following statements accurately describes the structural arrangement within a sarcomere during muscle contraction, according to the sliding filament theory?
In skeletal muscle, a motor neuron forms multiple synapses with a single muscle fiber, allowing for a greater degree of control over contraction.
In skeletal muscle, a motor neuron forms multiple synapses with a single muscle fiber, allowing for a greater degree of control over contraction.
Explain the crucial roles of ATP (adenosine triphosphate) in muscle contraction, focusing on the specific interactions with myosin and the stages of the cross-bridge cycle.
Explain the crucial roles of ATP (adenosine triphosphate) in muscle contraction, focusing on the specific interactions with myosin and the stages of the cross-bridge cycle.
The influx of ______ ions into the muscle fiber triggers the release of acetylcholine.
The influx of ______ ions into the muscle fiber triggers the release of acetylcholine.
Match the following muscle fiber components with their function in muscle contraction:
Match the following muscle fiber components with their function in muscle contraction:
Which of the following is the most accurate description of the role of T-tubules in excitation-contraction coupling?
Which of the following is the most accurate description of the role of T-tubules in excitation-contraction coupling?
Smooth muscle contraction is primarily regulated by the troponin-tropomyosin complex, similar to skeletal muscle.
Smooth muscle contraction is primarily regulated by the troponin-tropomyosin complex, similar to skeletal muscle.
Describe the structural differences between actin and myosin filaments and how these differences facilitate muscle contraction.
Describe the structural differences between actin and myosin filaments and how these differences facilitate muscle contraction.
The enzyme ______ catalyzes the breakdown of acetylcholine in the synaptic cleft, terminating its effect on the motor endplate.
The enzyme ______ catalyzes the breakdown of acetylcholine in the synaptic cleft, terminating its effect on the motor endplate.
According to the sliding filament theory, what happens to the H zone during muscle contraction?
According to the sliding filament theory, what happens to the H zone during muscle contraction?
The 'latent period' in muscle contraction refers to the time it takes for calcium ions to bind to troponin and initiate cross-bridge cycling.
The 'latent period' in muscle contraction refers to the time it takes for calcium ions to bind to troponin and initiate cross-bridge cycling.
Describe the role of ryanodine receptors in excitation-contraction coupling.
Describe the role of ryanodine receptors in excitation-contraction coupling.
The force created by a contracting muscle is termed ______, while the opposing force is termed ______.
The force created by a contracting muscle is termed ______, while the opposing force is termed ______.
Which of the following is responsible for generating the power stroke during muscle contraction?
Which of the following is responsible for generating the power stroke during muscle contraction?
The A band of the sarcomere shortens during muscle contraction due to the movement of myosin filaments.
The A band of the sarcomere shortens during muscle contraction due to the movement of myosin filaments.
Which of the following features distinguishes smooth muscle from skeletal muscle?
Which of the following features distinguishes smooth muscle from skeletal muscle?
Smooth muscle relies primarily on the sarcoplasmic reticulum (SR) as its sole source of calcium ions for contraction.
Smooth muscle relies primarily on the sarcoplasmic reticulum (SR) as its sole source of calcium ions for contraction.
Which metabolic adaptation allows skeletal muscle to continue functioning during short periods of oxygen deprivation?
Which metabolic adaptation allows skeletal muscle to continue functioning during short periods of oxygen deprivation?
The process by which a voluntary action transitions into an automatic one through repeated execution primarily involves changes in the ______ control level of the motor hierarchy.
The process by which a voluntary action transitions into an automatic one through repeated execution primarily involves changes in the ______ control level of the motor hierarchy.
Match each fatigue mechanism with its primary site of impact:
Match each fatigue mechanism with its primary site of impact:
In smooth muscle, what is the immediate consequence of calcium binding to calmodulin?
In smooth muscle, what is the immediate consequence of calcium binding to calmodulin?
Skeletal muscle fatigue always results from a complete depletion of ATP within the muscle fibers.
Skeletal muscle fatigue always results from a complete depletion of ATP within the muscle fibers.
How does the arrangement of actin and myosin filaments in smooth muscle differ structurally from that in skeletal muscle, and how does this difference affect the contractile mechanism?
How does the arrangement of actin and myosin filaments in smooth muscle differ structurally from that in skeletal muscle, and how does this difference affect the contractile mechanism?
Which characteristic is most indicative of a fast glycolytic (Type IIx) skeletal muscle fiber?
Which characteristic is most indicative of a fast glycolytic (Type IIx) skeletal muscle fiber?
In the excitation-contraction coupling of smooth muscle, the influx of extracellular Ca2+ through ______-gated channels is often a crucial initial step that triggers further Ca2+ release from intracellular stores.
In the excitation-contraction coupling of smooth muscle, the influx of extracellular Ca2+ through ______-gated channels is often a crucial initial step that triggers further Ca2+ release from intracellular stores.
Which of the following statements accurately describes the role of caveolae in smooth muscle cells?
Which of the following statements accurately describes the role of caveolae in smooth muscle cells?
Creatine phosphate provides a sustainable, long-term source of ATP for prolonged muscle activity.
Creatine phosphate provides a sustainable, long-term source of ATP for prolonged muscle activity.
How do muscarinic receptors play a role in the contraction of smooth muscle, and what intracellular signaling pathways are involved?
How do muscarinic receptors play a role in the contraction of smooth muscle, and what intracellular signaling pathways are involved?
Why is the ability to sustain tension over a broad range of muscle lengths particularly important in smooth muscle?
Why is the ability to sustain tension over a broad range of muscle lengths particularly important in smooth muscle?
Unlike skeletal muscle, smooth muscle contraction relies on the enzyme ______ to phosphorylate myosin, enabling it to bind with actin and initiate cross-bridge cycling.
Unlike skeletal muscle, smooth muscle contraction relies on the enzyme ______ to phosphorylate myosin, enabling it to bind with actin and initiate cross-bridge cycling.
Match each type of muscle fiber with its primary characteristic:
Match each type of muscle fiber with its primary characteristic:
Which of the following statements best explains central fatigue?
Which of the following statements best explains central fatigue?
In both skeletal and smooth muscle, the binding of calcium to troponin directly initiates the cross-bridge cycle.
In both skeletal and smooth muscle, the binding of calcium to troponin directly initiates the cross-bridge cycle.
Describe the key differences in the sarcoplasmic reticulum (SR) between skeletal and smooth muscle cells, and explain how these differences impact the regulation of muscle contraction.
Describe the key differences in the sarcoplasmic reticulum (SR) between skeletal and smooth muscle cells, and explain how these differences impact the regulation of muscle contraction.
During high-intensity exercise, what is the primary mechanism by which glycolysis contributes to muscle fatigue?
During high-intensity exercise, what is the primary mechanism by which glycolysis contributes to muscle fatigue?
The hierarchical organization of motor control starts in the ______, proceeds through intermediate brainstem and spinal cord circuits, and culminates in the activation of motor neurons.
The hierarchical organization of motor control starts in the ______, proceeds through intermediate brainstem and spinal cord circuits, and culminates in the activation of motor neurons.
Match each muscle type with its description:
Match each muscle type with its description:
How does extracellular fluid contribute to the increase of calcium during smooth muscle excitation?
How does extracellular fluid contribute to the increase of calcium during smooth muscle excitation?
Slow twitch, type 1, fibers are fast oxidative
Slow twitch, type 1, fibers are fast oxidative
What is the definition of central fatique?
What is the definition of central fatique?
During muscle activity, what happens to energy?
During muscle activity, what happens to energy?
Central fatigue refers to a decrease in the ability of the ______ to send signals to the muscles.
Central fatigue refers to a decrease in the ability of the ______ to send signals to the muscles.
Link runner type to muscle fiber.
Link runner type to muscle fiber.
What type of channels are invovled in calcium entry?
What type of channels are invovled in calcium entry?
Muscles often run out of ATP during excercise.
Muscles often run out of ATP during excercise.
List three differences between slow oxidative fibers and fast oxidative fibers
List three differences between slow oxidative fibers and fast oxidative fibers
Which of these features is not involved in mechanisms of central fatigue?
Which of these features is not involved in mechanisms of central fatigue?
Activation of ______ receptors can stimulate G-protein coupled receptors, leading to the production of IP3 and DAG, which then impact calcium levels and contraction
Activation of ______ receptors can stimulate G-protein coupled receptors, leading to the production of IP3 and DAG, which then impact calcium levels and contraction
Match the function to the location or muscle.
Match the function to the location or muscle.
Which is not a difference between skeletal and smooth muscle?
Which is not a difference between skeletal and smooth muscle?
T-tubules is not needed for smooth muscle function.
T-tubules is not needed for smooth muscle function.
How do different percentages of muscle fiber types affect activites such as running?
How do different percentages of muscle fiber types affect activites such as running?
Which is true about voluntary movement?
Which is true about voluntary movement?
______ is stored during rest/recovery, and used during activity.
______ is stored during rest/recovery, and used during activity.
Match the function to central or peripheral fatigue
Match the function to central or peripheral fatigue
Flashcards
Muscle Tissue
Muscle Tissue
Specialized tissue with the ability to contract and generate force for movement.
Skeletal Muscle
Skeletal Muscle
Attached to bones, striated, and under voluntary control for movement and heat production.
Cardiac Muscle
Cardiac Muscle
Found in the heart, striated, involuntary, and responsible for pumping blood.
Smooth Muscle
Smooth Muscle
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Sarcoplasm
Sarcoplasm
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Sarcolemma
Sarcolemma
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Myofibrils
Myofibrils
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Sarcomere
Sarcomere
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Myosin
Myosin
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Actin
Actin
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Z-line
Z-line
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H-Zone
H-Zone
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A-Band
A-Band
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I-Band
I-Band
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Motor Neuron
Motor Neuron
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Neuromuscular Junction
Neuromuscular Junction
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Acetylcholine (ACh)
Acetylcholine (ACh)
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T-Tubules
T-Tubules
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Sarcoplasmic Reticulum (SR)
Sarcoplasmic Reticulum (SR)
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Sliding Filament Theory
Sliding Filament Theory
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Cross-Bridge Formation
Cross-Bridge Formation
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Power Stroke
Power Stroke
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Slow Oxidative Fibers (Type I)
Slow Oxidative Fibers (Type I)
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Fast Oxidative Fibers (Type IIa)
Fast Oxidative Fibers (Type IIa)
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Fast Glycolytic Fibers (Type IIb)
Fast Glycolytic Fibers (Type IIb)
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Calmodulin
Calmodulin
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Kinase Enzyme
Kinase Enzyme
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Muscle Fatigue
Muscle Fatigue
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Tropomyosin
Tropomyosin
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Troponin
Troponin
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Depolarization
Depolarization
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Excitation-Contraction Coupling
Excitation-Contraction Coupling
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Hydrolysis of ATP
Hydrolysis of ATP
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Muscle tension
Muscle tension
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Load
Load
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Action potential
Action potential
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Latent period
Latent period
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Cross-bridge cycling
Cross-bridge cycling
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Acetylcholinesterase
Acetylcholinesterase
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Smooth Muscle Cells
Smooth Muscle Cells
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Caveolae
Caveolae
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Source of Ca2+ in Smooth Muscle
Source of Ca2+ in Smooth Muscle
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Ca2+ Release in Smooth Muscle
Ca2+ Release in Smooth Muscle
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Smooth Muscle Contraction
Smooth Muscle Contraction
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Energy Use in Muscle
Energy Use in Muscle
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Central Fatigue
Central Fatigue
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Peripheral Fatigue
Peripheral Fatigue
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Slow Twitch Fibers
Slow Twitch Fibers
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Fast Twitch Fibers
Fast Twitch Fibers
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Motor Control Hierarchy
Motor Control Hierarchy
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Study Notes
- Muscle tissue contracts to generate force, enabling voluntary (skeletal) and involuntary (cardiac/smooth) movements.
- Muscle tissues possess different properties from other cells.
- Contraction is muscle tissue's specialization, resulting in becoming shorter and tighter, allowing movement.
Types of Muscle Tissue
- Skeletal muscle is attached to bones via tendons, has a striated appearance, and is under voluntary control.
- Skeletal muscle functions include movement, joint stabilization, heat production, organ protection, and control of body entrances/exits.
- Cardiac muscle is located in the heart, striated, with cells connected by intercalated discs, and is under involuntary control.
- Cardiac muscle pumps blood, maintains blood pressure via heartbeats.
- Smooth muscle is found in hollow organ walls, lacks striations and is under involuntary control.
- Smooth muscle regulates vessel diameter for circulation and moves substances in digestive, urinary, reproductive, and respiratory systems.
- Different muscle types have different structures and functions in the body.
- There are 3 types of muscle tissue in the body: skeletal, cardiac and smooth.
- Skeletal and cardiac muscle tissue is striated, while smooth muscle is non-striated.
Muscle Fiber Structure and Sarcomere
- A skeletal muscle is made of muscle fibers (cells), myofibrils, and sarcomeres.
- Muscle fibers contain sarcoplasm (cytoplasm), a sarcolemma (cell membrane), and myofibrils (contractile units).
- The sarcoplasm is the cytoplasm of a muscle cell with the cell membrane being the sarcolemma.
- Sarcomeres are the functional units within myofibrils.
- Each myofibril contains sarcomeres.
- Each sarcomere contains myosin and actin.
- Myosin (thick filament) consists of strands of protein with tiny hooks.
- Myosin has a tail and a head.
- Myosin heads stick out at an angle of 120 degrees, and myosin includes an ATPase site.
- Myosin heads have affinity for actin, and myosin tails have affinity for myosin.
- Actin (thin filament) comprise thinner strands that act as tracks for myosin.
- F-actin consists of helical filaments made of two strands of fibrous actin.
- F-actin is polymer of ~200 globular actins, called G-actins with myosin-head binding sites.
- Myosin and actin filaments overlap in the sarcomere, surrounded by each other.
- The Z-line marks the boundary of each sarcomere.
- The H-zone is the central region of the sarcomere containing only myosin, visible when the muscle is relaxed.
- The A-band spans the entire length of the myosin filaments and remains constant during contraction.
- The I-band contains only actin filaments and shortens during contraction.
- Skeletal muscle is striated, because of the highly regular arrangements of contractile filaments which overlap.
- Smooth muscle cells are elongated and smaller than skeletal muscle cells.
- Actin and myosin in smooth muscle overlap in an X-shape.
- Smooth muscle does not have sarcomeres or Z lines.
Muscle Contraction
- Muscle tension is the force created by a contracting muscle.
- Load is the weight or force opposing muscle contraction.
- A motor neuron stimulates a muscle fibre to contract.
- An action potential causes the muscle fibre to contract, which generates tension.
- Study of the sarcomere via electron microscopy led to the sliding filament theory of muscle contraction.
- During muscle contraction, Z-lines move closer to the center.
- Myosin bands do not change in length.
- Thin actin filaments slide toward the center of the sarcomere along thick myosin filaments during contraction.
How Muscle Contraction Happens: The Sliding Filament Theory
- A motor neuron sends an action potential (electrical signal).
- Acetylcholine (ACh) is released at the neuromuscular junction, binding to muscle cell receptors and allowing sodium ions to enter, which spreads an electrical signal.
- This process occurs at the motor endplate.
- Each axon forms a synapse with one or more muscle fibres, collectively known as the neuromuscular junction (NMJ).
- Neuronal action potential depolarizes the motor endplate in the muscle fibre.
- Action potential is released (ACh, neurotransmitter).
- ACh binds to nicotinic acetylcholine receptors (nAChR; ligand-gated ion channels), which causes the nAChRs to open.
- Sodium ions flow into the muscle fibre, causing local depolarisation of motor endplate.
- Action of acetylcholine is terminated by acetylcholinesterase, which breaks down ACh.
- Ligand-gated ion channels allow Na+ ions to flow through into the muscle.
- Excitation-contraction coupling involves the signal traveling along T-tubules, causing the sarcoplasmic reticulum (SR) to release calcium ions (Ca²⁺).
- The latent period is when the action potential happens.
- Calcium binds to troponin on actin, exposing myosin binding sites.
- Cross-bridge cycling involves myosin heads attaching to actin (cross-bridge formation).
- Myosin heads are bound to actin to form cross-bridges.
- The power stroke occurs when myosin heads pull actin filaments closer, requiring ATP.
- The Sliding Filament Theory can be viewed in action at https://www.youtube.com/watch?v=BVcgO4p88AA between 0m0sec – 0m40sec.
- ATP binds to myosin heads to release them from actin.
- ATP is used to re-cock myosin heads and pull the actin with it.
- Repeated cycles shorten the muscle, generating movement.
- Excitation-contraction coupling in smooth muscle has similarities to skeletal muscle as Ca2+ binding initiates contraction and cross-bridge cycling (of myosin and actin) produces contraction.
- Excitation-contraction coupling in smooth muscle differs to skeletal muscle in with the source, release , and use of Ca2+ in contraction
Cross-Bridge Cycling
- Cross-bridge cycling refers to the action of myosin, actin, troponin, tropomyosin, calcium, and ATP.
- ATP provides energy for cross-bridge cycling.
- ATP has two distinct roles in muscle contraction: binding to musing and hydrolisis.
- ATP binding to myosin disrupts the actin-myosin link.
- ATP hydrolysis produces energy for cross-bridge movement ('resets' the myosin head).
Muscle Relaxation
- Brain signals stop, and calcium ions are pumped back into the sarcoplasmic reticulum.
- Tropomyosin covers actin filaments, blocking myosin attachment, thus halting contraction.
Different Muscle Fiber Types
- Slow oxidative fibers (Type I) use oxygen aerobically for endurance, do not produce much power, and resist fatigue.
- Fast oxidative fibers (Type IIa) use oxygen, work faster, suitable for strength and endurance, and fatigue quicker than Type I.
- Fast glycolytic fibers (Type IIb) use glycolysis, contract quickly/powerfully, fatigue rapidly, suitable for short/explosive activities.
- Different types of physical activity lead to different percentages of muscle fibre types in skeletal muscle.
- There are different types of skeletal muscle fibre.
- Slow twitch fibers (ST I) are slow oxidative.
- Fast twitch fibers (FTa or FTb, or IIa/IIb) are fast oxidative / fast glycolytic.
- Muscle fibre types differ in metabolism, speed of rapid shortening, and resistance to fatigue.
- Muscle fibre types allow muscles to carry out different types of movement.
Smooth Muscle Contraction
- Smooth muscle contracts slowly and sustains contraction longer.
- Calmodulin (not troponin) controls contraction.
- Calcium binds to calmodulin, activating a kinase enzyme that phosphorylates myosin, enabling actin binding.
- This process is slower and more controlled than in skeletal muscle.
- Cytosolic Ca2+ associates with calmodulin to initiate contraction.
- SR (sarcoplasmic reticulum) is in caveolae, which are close to the sarcolemma.
- Contraction leads to quick depolarisation.
Muscle Fatigue
- Muscle fatigue occurs when the muscle cannot generate force.
- Causes include ATP depletion.
- Causes include lactic acid build up.
- Causes include ion imbalance.
- Smooth muscle resists fatigue due to lower energy use and prolonged contraction ability.
- Usually 30% of ATP available is used in strenuous exercise.
Muscle Contraction Overview:
- Actin and myosin filaments slide past each other (cross-bridge cycling).
- Myosin heads bind to actin.
- ATP provides energy.
- Calcium ions (Ca²⁺) control contraction.
- Troponin and tropomyosin regulate access to binding sites for myosin on actin.
- ATP binds to myosin heads, causing them to detach from actin (if previously bound).
- When ATP is hydrolyzed, the myosin head "re-energizes".
- Myosin then attaches to specific binding sites on the actin filament, forming a cross-bridge.
- Myosin heads pivot, pulling the actin filament during the power stroke.
Regulation:
- Tropomyosin blocks myosin-binding sites on actin.
- Troponin has a binding site for calcium.
- When calcium levels are low, tropomyosin blocks the myosin-binding sites on actin, preventing contraction.
- Rising calcium levels cause tropomyosin to shift, exposing the binding sites and allowing myosin to bind to actin.
What Triggers Contraction?
- The contraction is triggered by an increase in intracellular calcium (Ca²⁺).
- A motor neuron sends a signal (action potential) to the muscle fiber.
- Acetylcholine (ACh) is released.
- Action potential spreads along the muscle fiber and through the T-tubules.
- The sarcoplasmic reticulum (SR) releases calcium into the muscle fiber's cytoplasm.
- Calcium ions bind to troponin, which causes tropomyosin to shift, exposing the binding sites on actin for myosin.
- Troponin changes shape, which causes tropomyosin to move and expose the binding sites on actin.
- Once the action potential ends, calcium is pumped back into the sarcoplasmic reticulum (SR).
- As calcium levels drop, troponin goes back to its original shape, causing tropomyosin to block the binding sites on actin again.
ATP and Its Role:
- Binding to Myosin: When ATP binds to myosin, it breaks the bond between myosin and actin.
- Hydrolysis of ATP: ATP is broken down into ADP and inorganic phosphate (Pi), which provides the energy for the myosin head to move (reset) and perform the power stroke.
Excitation Contraction Coupling Relies On:
- T-tubule and sarcoplasmic reticulum.
- Linkage between the structures: Dihydropyridine (DHP) and ryanodine receptors.
- Increase in intracellular calcium.
- Ca2+ ATPase lowers intracellular calcium.
- Action occurs for Myosin, actin, troponin, tropomyosin, calcium and ATP between 0m40sec – 2m00.
- Action potential in T-tubule membrane causes SR Ca2+ release channels to open.
- Ryanodine receptors (foot structures) open Ca2+ release channels.
- Ca2+ is pumped back into the SR by Ca2+ ATPase.
- There needs increased intracellular Ca2+ for contraction.
- Source of Ca2+ sarcoplasmic reticulum (SR).
- SR membrane contains Ca2+ release channels that are voltage sensitive.
- Channels are closed at 'rest'.
- T-tubules are needed for quick depolarisation.
- There are no T-Tubules in smooth muscle cells.
Smooth Muscle Information
- In the smooth muscle, actin and myosin do not form sarcomeres
- Sarcoplasmic reticulum is situated close to the plasma membrane
- Calcium source can be extracellular and from the SR
- The sarcoplasmic reticulum is situated close to the plasma membrane
- Ca²⁺ enters from extracellular fluid and ligand-gated channels initial Ca2+ entry, which triggers voltage-gated Ca2+ channels allowing further Ca2+ entry
- “Second messenger” signalling in the cell triggers Ca2+ release from the sarcoplasmic reticulum
- This is by muscarinic ACh receptor stimulation, G-protein coupled receptors, and inosital
- If IP3/DAG is involved contraction of smooth muscle takes place.
- Smooth muscle uses Myosin light-chain kinase (MLCK), and calcium
Metabolism In Muscle
- ATP is available from multiple sources in muscle: creatine phosphate, glycogen, and fatty acids/amino acids
- Energy is stored during rest/recovery and used during activity
- Fatigue is not caused by a lack of ATP
- At rest energy is stored, while at peak activity energy is used
- During recovery, energy stores are re-built
Fatigue
- Central fatigue is a decrease in the ability of the central nervous system (CNS) to send signals to the muscles, leading to a reduction in voluntary activation and performance.
- Central fatigue relates to the motor cortex as mechanisms involve reduced neural drive, decreased frequency/synchronization of motoneurons, and impaired motivation/effort perception
- Peripheral fatigue refers to changes or impairments in the neuromuscular system, including the neuromuscular junction, muscle fibers, or muscle metabolism.
- Peripheral fatigue is caused by mechanisms such as muscle bioenergetics (e.g., ATP depletion, lactate accumulation), muscle damage, impaired excitation-contraction coupling, or neuromuscular transmission failure.
Control Of Movement
- The motor control hierarchy controls movement from the brain.
- Flexion and extension of antagonistic muscles moves joints.
- Voluntary movements involve conscious awareness and involuntary movements involve unconscious or automatic actions.
- Learned actions start as voluntary but gradually become automatic
- The brain controls most movement through something called the motor control hierarchy
- Movements are of two types
- Voluntary – conscious awareness
- Involuntary – unconscious or automatic
Additional Resources:
- Recommended reading: Human Physiology: An Integrated Approach by Dee Unglaub Silverthorn.
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