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Questions and Answers
What initiates the process of excitation-contraction coupling in muscle fibers?
What initiates the process of excitation-contraction coupling in muscle fibers?
- Generation of an action potential at the myoneural junction (correct)
- Release of neurotransmitters at the synapse
- Activation of myofibrils by calcium
- Spreading of calcium throughout the muscle fiber
Which structure is responsible for the rapid release of calcium during excitation-contraction coupling?
Which structure is responsible for the rapid release of calcium during excitation-contraction coupling?
- T-tubules
- Terminal cisternae of the triads (correct)
- Mitochondria
- Endoplasmic reticulum
What role does calcium play in the process of muscle contraction?
What role does calcium play in the process of muscle contraction?
- It directly contracts the muscle fibers
- It initiates the production of ATP
- It binds to myofibrils and triggers shortening (correct)
- It inhibits muscle relaxation
What happens to calcium concentration around myofibrils when depolarization of the sarcolemma ceases?
What happens to calcium concentration around myofibrils when depolarization of the sarcolemma ceases?
What is the primary component of the A-bands in myofibrils?
What is the primary component of the A-bands in myofibrils?
What is the diameter of myosin filaments mentioned in the content?
What is the diameter of myosin filaments mentioned in the content?
At which junction do the longitudinal sarcotubules terminate?
At which junction do the longitudinal sarcotubules terminate?
What are myofibrils primarily composed of?
What are myofibrils primarily composed of?
What is the role of satellite cells in muscle tissue?
What is the role of satellite cells in muscle tissue?
At what age is Gower’s Sign often apparent in individuals with muscle issues?
At what age is Gower’s Sign often apparent in individuals with muscle issues?
Which of the following best describes atrophy in muscle tissue?
Which of the following best describes atrophy in muscle tissue?
What type of cells primarily form myotubes during muscle development?
What type of cells primarily form myotubes during muscle development?
What is the primary function of mitochondria (sarcosomes) in muscle tissue?
What is the primary function of mitochondria (sarcosomes) in muscle tissue?
Muscle fibers can increase in size due to which process?
Muscle fibers can increase in size due to which process?
The thickness of muscle fibers can vary considerably within the same muscle. What usually causes this variance?
The thickness of muscle fibers can vary considerably within the same muscle. What usually causes this variance?
What are myofibrils primarily composed of?
What are myofibrils primarily composed of?
What type of muscle tone do smooth muscles in the walls of blood vessels maintain under normal circumstances?
What type of muscle tone do smooth muscles in the walls of blood vessels maintain under normal circumstances?
Which hormones are known to cause vasoconstriction in smooth muscles?
Which hormones are known to cause vasoconstriction in smooth muscles?
What is the role of postganglionic autonomic nerve fibers in relation to smooth muscle?
What is the role of postganglionic autonomic nerve fibers in relation to smooth muscle?
How do changes in estrogen levels affect uterine smooth muscle?
How do changes in estrogen levels affect uterine smooth muscle?
What is the effect of bradykinin and prostaglandin on smooth muscle tone?
What is the effect of bradykinin and prostaglandin on smooth muscle tone?
Which part of the digestive tract contains striated muscle?
Which part of the digestive tract contains striated muscle?
What is the main function of smooth muscle at the pylorus?
What is the main function of smooth muscle at the pylorus?
What happens to the length of the A-bands during the contraction and relaxation cycle?
What happens to the length of the A-bands during the contraction and relaxation cycle?
In which part of the digestive system are villi present?
In which part of the digestive system are villi present?
What are the segments of myofibrils between successive Z-lines called?
What are the segments of myofibrils between successive Z-lines called?
What happens to smooth muscle cells during anesthesia according to the clinical significance mentioned?
What happens to smooth muscle cells during anesthesia according to the clinical significance mentioned?
Which type of motor units contract more slowly due to containing red fibers?
Which type of motor units contract more slowly due to containing red fibers?
Which of the following correctly describes the structure of myofibrils in muscle tissue?
Which of the following correctly describes the structure of myofibrils in muscle tissue?
What type of muscle is found in the walls of the respiratory passages from the trachea to the alveolar ducts?
What type of muscle is found in the walls of the respiratory passages from the trachea to the alveolar ducts?
What type of mitochondria are found in the subsarcolemmal region?
What type of mitochondria are found in the subsarcolemmal region?
Which property of red fibers allows them to be very resistant to fatigue?
Which property of red fibers allows them to be very resistant to fatigue?
How does smooth muscle in the large intestine primarily function?
How does smooth muscle in the large intestine primarily function?
What is a consequence of smooth muscle cell migration in atherosclerosis?
What is a consequence of smooth muscle cell migration in atherosclerosis?
What structural feature bisects each I-band?
What structural feature bisects each I-band?
How are the slender, paired mitochondria positioned in relation to Z-lines?
How are the slender, paired mitochondria positioned in relation to Z-lines?
Which fibers are identified as the largest among all fiber types?
Which fibers are identified as the largest among all fiber types?
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Study Notes
Excitation-Contraction Coupling
- Initiated at the myoneural junction with the generation of an action potential traveling along the sarcolemma and T-tubules.
- Action potential activates calcium release from the sarcoplasmic reticulum at the T-tubules and terminal cisternae interface.
- Calcium binds to myofibrils in the sarcoplasm, initiating muscle shortening.
- Upon cessation of nerve impulse, calcium is actively transported back into terminal cisternae, resulting in muscle relaxation.
Myofibrils Structure
- Myofibrils consist of smaller myofilaments, primarily myosin and actin.
- Myosin filaments measure 1.5 μm in length and 15 nm in diameter, located in A-bands.
- Sarcotubules within myofibrils connect with terminal cisternae at A-I junctions, creating triads essential for muscle function.
- Sarcomeres, defined by segments between Z-lines, contain A-bands and I-bands which define contraction cycles.
Muscle Development and Repair
- Myoblasts, the embryonic precursors, fuse to form myotubes, leading to differentiated muscle fibers.
- Muscle fibers can undergo hypertrophy (increase in size) and atrophy (decrease in size).
- Satellite cells assist in muscle repair but skeletal muscle has limited regenerative ability in adults.
- Gower’s Sign is observed in children with muscle weakness, reflecting impaired ability to rise from the ground.
Mitochondrial Organization
- Mitochondria cluster around myofibrils to supply ATP necessary for muscle contraction, arranged in longitudinal columns within sarcoplasm.
- Mitochondria are abundant near Z-lines, positioned to maximize energy availability during muscle activity.
Muscle Fiber Types
- White fibers (fast-twitch) are the largest muscle fiber type, adapted for powerful and rapid contractions.
- Red fibers (slow-twitch) contract more slowly, are resistant to fatigue, and effective for maintaining posture.
Smooth Muscle Physiology
- Shortening in smooth muscle occurs through a sliding mechanism similar to that in striated muscle, involving actin and myosin filaments.
- Innervation is provided by post-ganglionic autonomic nerve fibers that influence contraction via synaptic contacts.
- Vascular smooth muscle maintains muscle tone, modulated by hormones like norepinephrine and bradykinin, influencing vasoconstriction and vasodilation.
Clinical Relevance of Smooth Muscle
- Migration of smooth muscle cells in atherosclerosis contributes to plaque formation, affecting vascular health.
- During anesthesia, smooth muscles can become immobile, complicating respiration, highlighting the importance of proper intubation techniques.
Tissues Involving Muscle Types
- Esophagus has striated muscle; smooth muscle is prominent in the pyloric sphincter, stomach, and intestines.
- Smooth muscle is also found in respiratory passages, unable to gain structure in alveoli, essential for maintaining airway function.
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