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Questions and Answers
What is the role of calcium in the excitation-contraction coupling of cardiac muscle?
What is the role of calcium in the excitation-contraction coupling of cardiac muscle?
- Propagates the action potential to dyads
- Binds to myofibrils during contraction (correct)
- Causes relaxation by returning to the sarcoplasmic reticulum
- Generates action potential in pacemaker cells
How does the length of the contractile cell action potential in cardiac muscle prevent tetanus?
How does the length of the contractile cell action potential in cardiac muscle prevent tetanus?
- By having a prolonged refractory period (correct)
- By propagating action potentials slowly
- By inhibiting the binding of calcium to myofibrils
- By releasing an insufficient amount of calcium
How does the resting sarcomere length in cardiac muscle compare to optimal length?
How does the resting sarcomere length in cardiac muscle compare to optimal length?
- It varies depending on muscle contractility
- It is greater than optimal length
- It is at optimal length
- It is less than optimal length (correct)
What differentiates cardiac muscle from skeletal muscle regarding contraction?
What differentiates cardiac muscle from skeletal muscle regarding contraction?
Which statement best describes the excitation-contraction coupling of skeletal muscle?
Which statement best describes the excitation-contraction coupling of skeletal muscle?
What effect does the blood filling in the ventricles have on cardiac muscle?
What effect does the blood filling in the ventricles have on cardiac muscle?
What type of muscle fiber has physiological and histological features intermediate between the other two types?
What type of muscle fiber has physiological and histological features intermediate between the other two types?
Which type of cells in the heart are responsible for initiating action potentials?
Which type of cells in the heart are responsible for initiating action potentials?
What is the function of intercalated disks in cardiac muscle cells?
What is the function of intercalated disks in cardiac muscle cells?
What is the primary role of pacemaker cells in the heart's conduction system?
What is the primary role of pacemaker cells in the heart's conduction system?
Which component is significantly less developed in cardiac muscle cells compared to skeletal muscle fibers?
Which component is significantly less developed in cardiac muscle cells compared to skeletal muscle fibers?
What percentage of myocardial cells are made up of pacemaker cells in the heart?
What percentage of myocardial cells are made up of pacemaker cells in the heart?
What is the correct sequence of events at the neuromuscular junction for skeletal muscle contraction?
What is the correct sequence of events at the neuromuscular junction for skeletal muscle contraction?
What is the result of calcium binding to the myofibrils during skeletal muscle contraction?
What is the result of calcium binding to the myofibrils during skeletal muscle contraction?
What happens when calcium is released from the myofibrils during skeletal muscle relaxation?
What happens when calcium is released from the myofibrils during skeletal muscle relaxation?
What occurs when action potentials are propagated down the somatic motor neuron at the neuromuscular junction?
What occurs when action potentials are propagated down the somatic motor neuron at the neuromuscular junction?
What role do nicotinic receptors play at the motor-end plate during skeletal muscle contraction?
What role do nicotinic receptors play at the motor-end plate during skeletal muscle contraction?
What is the effect of the end plate potential spreading across the muscle fiber during skeletal muscle contraction?
What is the effect of the end plate potential spreading across the muscle fiber during skeletal muscle contraction?
What happens at the end of the power stroke in muscle contraction?
What happens at the end of the power stroke in muscle contraction?
In skeletal muscle, what induces a conformational change in the thin filament allowing myosin heads to cross-bridge with actin?
In skeletal muscle, what induces a conformational change in the thin filament allowing myosin heads to cross-bridge with actin?
Which statement best describes an isotonic contraction?
Which statement best describes an isotonic contraction?
What is the role of afterload in the force-velocity relationship in muscle contraction?
What is the role of afterload in the force-velocity relationship in muscle contraction?
What happens during temporal summation in muscle contraction?
What happens during temporal summation in muscle contraction?
In skeletal muscle, what is the primary function of spatial summation?
In skeletal muscle, what is the primary function of spatial summation?
At what stage does ATP binding destabilize the myosin-actin interaction in muscle contraction?
At what stage does ATP binding destabilize the myosin-actin interaction in muscle contraction?
What defines the length-tension relationship in muscle mechanics?
What defines the length-tension relationship in muscle mechanics?
Which type of muscle tissue makes up approximately 30-45% of the total body weight?
Which type of muscle tissue makes up approximately 30-45% of the total body weight?
What is the function of the perimysium in skeletal muscle organization?
What is the function of the perimysium in skeletal muscle organization?
Which protein wraps around actin filaments and covers the myosin-binding sites in sarcomeres?
Which protein wraps around actin filaments and covers the myosin-binding sites in sarcomeres?
What is the function of troponin-I (Tn-I) in sarcomeres during muscle contraction?
What is the function of troponin-I (Tn-I) in sarcomeres during muscle contraction?
Where are triads located in skeletal and cardiac muscle cells?
Where are triads located in skeletal and cardiac muscle cells?
In skeletal muscle, what is the primary function of nebulin and titin?
In skeletal muscle, what is the primary function of nebulin and titin?
Which region of the sarcomere contains only thick (myosin) filaments?
Which region of the sarcomere contains only thick (myosin) filaments?
What is the primary function of the endomysium in skeletal muscle organization?
What is the primary function of the endomysium in skeletal muscle organization?
Which organelle serves as a major store for calcium in muscle cells?
Which organelle serves as a major store for calcium in muscle cells?
What is the primary function of transverse tubules (T-tubules) in muscle cells?
What is the primary function of transverse tubules (T-tubules) in muscle cells?
Study Notes
Skeletal Muscle Organization
- Skeletal muscles make up 30-45% of total body weight
- Under voluntary control and mostly attached to bones
- Functions: produce skeletal movement, maintain posture and body position, protect internal organs, and generate heat
- Three connective tissue layers: epimysium, perimysium, and endomysium
- Each skeletal muscle fiber has a sarcolemma (cell membrane), transverse tubules (T-tubules), and a sarcoplasmic reticulum (SR)
Sarcomere Structure
- Sarcomeres are the contractile units of skeletal and cardiac muscle
- A-band contains thick (myosin) and thin filaments (actin)
- I-band contains only thin filaments
- Z-line anchors thin filaments to the sarcolemma
- H-zone contains only thick filaments
- Sarcomeres shorten during muscle contraction
Actin Filaments
- Actin chains are intertwined with troponin and tropomyosin proteins
- Actin has a myosin-binding site
- Troponin and tropomyosin regulate muscle contraction
Myosin Filaments
- Myosin molecules form a protein chain with a head and a tail
- Myosin head has a heavy chain (HC) and a light chain (LC)
- Heavy chain contains an ATP binding site and a binding site for actin
- Elastic hinge region allows the head to swivel and move (power stroke)
Excitation-Contraction Coupling
- Excitation-contraction coupling is the process in which an action potential causes calcium concentration to increase in the cytosol, leading to contraction of the muscle
- Steps: excitation, coupling, contraction, and relaxation
- Calcium binds to troponin and tropomyosin, allowing myosin heads to cross-bridge with actin
Neuromuscular Junction
- The neuromuscular junction is the synapse between a motor neuron and a muscle fiber
- Sequence of events: action potential propagation, calcium influx, ACh release, binding to nicotinic receptors, and muscle contraction
Muscle Contraction and Relaxation
- Muscle twitch: one cycle of excitation-contraction coupling
- Types of contraction: isometric (no shortening) and isotonic (shortening with constant tension)
- Types of isotonic contractions: concentric (shortening) and eccentric (lengthening)
- Length-tension relationship: the relationship between fiber length and force produced
- Force-velocity relationship: the velocity of shortening as a product of changes in afterload
Cardiac Muscle
- The heart is a hollow muscular pump that pumps blood throughout the vasculature
- Ventricular muscle cells: striated muscle cells with two nuclei, rich in mitochondria, and less developed SR
- Cells are connected end-to-end by gap junctions, forming a functional syncytium
- Pacemaker cells initiate action potentials necessary for cardiac muscle contraction
Excitation-Contraction Coupling in Cardiac Muscle
- Similar to skeletal muscle, but with differences in SR and calcium release
- No tetanus in cardiac muscle due to the length of the contractile cell action potential
- Graded contractions possible due to the heart's ability to increase contractile force under changing conditions
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Description
Test your knowledge on the muscle contraction process. From myosin releasing ADP to ATP binding destabilizing the myosin-actin interaction, each step is crucial for muscle fiber shortening.
