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What are three additional important roles of skeletal muscle besides producing movement?
What are three additional important roles of skeletal muscle besides producing movement?
What is the primary function of the sarcolemma in muscle fibers?
What is the primary function of the sarcolemma in muscle fibers?
Which band in a myofibril contains only thin filaments?
Which band in a myofibril contains only thin filaments?
What is the structure that serves as the contractile unit of a muscle fiber?
What is the structure that serves as the contractile unit of a muscle fiber?
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What is the composition of the A band in a myofibril?
What is the composition of the A band in a myofibril?
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Which property gives skeletal muscle its striated appearance?
Which property gives skeletal muscle its striated appearance?
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Where is the M line located within the H zone of a myofibril?
Where is the M line located within the H zone of a myofibril?
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What is the primary neurotransmitter that stimulates skeletal muscle at the neuromuscular junction?
What is the primary neurotransmitter that stimulates skeletal muscle at the neuromuscular junction?
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What type of filaments make up the thick filaments in skeletal muscle?
What type of filaments make up the thick filaments in skeletal muscle?
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What occurs immediately after the calcium channels open in the axon terminal of the motor neuron?
What occurs immediately after the calcium channels open in the axon terminal of the motor neuron?
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What happens to the membrane potential of the sarcolemma when enough acetylcholine is released?
What happens to the membrane potential of the sarcolemma when enough acetylcholine is released?
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What is the term for the gap between the nerve and muscle cell at the neuromuscular junction?
What is the term for the gap between the nerve and muscle cell at the neuromuscular junction?
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In the process of muscle stimulation, which ion diffuses into the axon terminal first?
In the process of muscle stimulation, which ion diffuses into the axon terminal first?
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Which statement is true regarding the nerve and muscle cell interaction?
Which statement is true regarding the nerve and muscle cell interaction?
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What role do sodium ions play after the binding of acetylcholine to the sarcolemma receptors?
What role do sodium ions play after the binding of acetylcholine to the sarcolemma receptors?
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What is the result of more sodium ions entering the muscle cell than potassium ions leaving during depolarization?
What is the result of more sodium ions entering the muscle cell than potassium ions leaving during depolarization?
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What occurs first when a nerve impulse reaches the axon terminal of a motor neuron?
What occurs first when a nerve impulse reaches the axon terminal of a motor neuron?
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What substance is contained within the synaptic vesicles at the axon terminal?
What substance is contained within the synaptic vesicles at the axon terminal?
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What is the role of calcium ions (Ca2+) in the events at the neuromuscular junction?
What is the role of calcium ions (Ca2+) in the events at the neuromuscular junction?
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What is the correct sequence of events that occurs at the neuromuscular junction?
What is the correct sequence of events that occurs at the neuromuscular junction?
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What structure does ACh bind to after its release in the neuromuscular junction?
What structure does ACh bind to after its release in the neuromuscular junction?
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Where does the nerve impulse reach before calcium channels open?
Where does the nerve impulse reach before calcium channels open?
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What happens to ACh after it binds to its receptors on the muscle fiber?
What happens to ACh after it binds to its receptors on the muscle fiber?
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Which of the following NOT a component involved in the neuromuscular junction?
Which of the following NOT a component involved in the neuromuscular junction?
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What happens to the thin filaments during muscle contraction?
What happens to the thin filaments during muscle contraction?
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Which of the following statements best describes graded responses in skeletal muscle?
Which of the following statements best describes graded responses in skeletal muscle?
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How can graded responses in a skeletal muscle be achieved?
How can graded responses in a skeletal muscle be achieved?
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What characterizes a muscle twitch?
What characterizes a muscle twitch?
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What occurs when muscle impulses are delivered at a rapid rate?
What occurs when muscle impulses are delivered at a rapid rate?
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What is the effect of stimulating more muscle fibers at once?
What is the effect of stimulating more muscle fibers at once?
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What is the role of ATP in muscle contraction?
What is the role of ATP in muscle contraction?
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Which of the following accurately describes the all-or-none principle of muscle fiber contraction?
Which of the following accurately describes the all-or-none principle of muscle fiber contraction?
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What is the primary action of supination in the forearm?
What is the primary action of supination in the forearm?
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Which term describes the movement of turning the sole of the foot laterally?
Which term describes the movement of turning the sole of the foot laterally?
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What role does a fixator play in muscle movements?
What role does a fixator play in muscle movements?
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Which movement involves the thumb touching the tips of the other fingers?
Which movement involves the thumb touching the tips of the other fingers?
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What defines plantar flexion in terms of foot movement?
What defines plantar flexion in terms of foot movement?
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What happens during pronation of the forearm?
What happens during pronation of the forearm?
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Which muscle type is specifically responsible for opposing a prime mover?
Which muscle type is specifically responsible for opposing a prime mover?
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What does inversion refer to in foot movements?
What does inversion refer to in foot movements?
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Study Notes
Muscle Functions
- Skeletal muscles maintain posture, stabilize joints, and generate heat in addition to producing movement.
Microscopic Anatomy of Skeletal Muscle
- The sarcolemma is the specialized plasma membrane of a muscle cell.
- Myofibrils are long organelles within muscle cells; their light (I) and dark (A) bands create the striated appearance.
- The I band contains only thin filaments and is interrupted by the Z disc.
- The A band contains the entire length of thick filaments; it includes the lighter H zone and the M line in its center.
- The sarcomere, the contractile unit of a muscle fiber, is the structural and functional unit of skeletal muscle. It's composed of myofilaments (thick = myosin; thin = actin).
Motor Units
- A motor unit consists of one motor neuron and all the muscle fibers it stimulates. Axon terminals branch to innervate multiple muscle fibers within a motor unit.
Neuromuscular Junction and Action Potential
- The neuromuscular junction is where a motor neuron's axon terminal meets a muscle fiber's sarcolemma.
- Acetylcholine (ACh) is the neurotransmitter that stimulates skeletal muscle.
- The synaptic cleft is the gap between nerve and muscle.
- Nerve impulse arrival triggers calcium ion entry into the axon terminal, causing ACh release.
- ACh binds to sarcolemma receptors, increasing sodium ion permeability; more sodium ions enter than potassium ions leave, causing depolarization.
Events at the Neuromuscular Junction
- A nerve impulse reaching the axon terminal opens calcium channels, allowing calcium ions to enter.
- This causes synaptic vesicles to release ACh into the synaptic cleft.
- ACh diffuses across, binds to sarcolemma receptors, and initiates depolarization.
Contraction of a Skeletal Muscle as a Whole
- Muscle fiber contraction is "all-or-none".
- Graded responses result from varying the frequency or number of stimulated muscle cells.
- A muscle twitch is a single, brief contraction, not typical of normal function.
- Summation of contractions occurs with rapid stimulation, producing sustained contraction.
Special Movements
- Dorsiflexion and plantar flexion refer to upward and downward movements of the foot, respectively.
- Inversion turns the sole of the foot medially; eversion turns it laterally.
- Supination is lateral forearm rotation (palm anterior, radius and ulna parallel).
- Pronation is medial forearm rotation (palm posterior, radius and ulna crossed).
- Opposition is the thumb's movement to touch other finger tips.
Interactions of Skeletal Muscles in the Body
- Muscles pull, not push. Opposing muscle groups lie on opposite sides of joints.
- The prime mover is the main muscle responsible for a movement.
- Antagonists oppose prime movers.
- Synergists aid prime movers or reduce undesirable movements.
- Fixators stabilize the origin of a prime mover.
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Description
Test your knowledge on the functions and microscopic anatomy of skeletal muscles. Explore topics such as motor units and the neuromuscular junction, and understand how these components work together to enable movement and maintain posture. Dive deep into the intricacies of muscle fiber structure and function.
