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Questions and Answers
Which type of muscle is responsible for voluntary control?
Which type of muscle is responsible for voluntary control?
What is the primary location of cardiac muscle tissue?
What is the primary location of cardiac muscle tissue?
How is the contraction of smooth muscle typically controlled?
How is the contraction of smooth muscle typically controlled?
Which of the following is NOT a function of skeletal muscle?
Which of the following is NOT a function of skeletal muscle?
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Which muscle type contains intercalated discs?
Which muscle type contains intercalated discs?
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What characterizes isotonic contractions?
What characterizes isotonic contractions?
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Which of the following is an example of an isometric contraction?
Which of the following is an example of an isometric contraction?
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What is the primary purpose of muscle tone?
What is the primary purpose of muscle tone?
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During which type of contraction do muscle filaments attempt to slide but cannot due to an immovable object?
During which type of contraction do muscle filaments attempt to slide but cannot due to an immovable object?
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Muscle tone results from the systematic stimulation of which of the following?
Muscle tone results from the systematic stimulation of which of the following?
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What is the primary role of an antagonist muscle in movement?
What is the primary role of an antagonist muscle in movement?
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Which type of muscle is responsible for reducing unwanted or excess motion in a joint?
Which type of muscle is responsible for reducing unwanted or excess motion in a joint?
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What is the function of a fixator muscle during movement?
What is the function of a fixator muscle during movement?
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Which muscle type primarily leads the movement in a given action?
Which muscle type primarily leads the movement in a given action?
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Which of the following statements is true about synergist muscles?
Which of the following statements is true about synergist muscles?
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What is one of the primary functions of skeletal muscle, aside from producing movement?
What is one of the primary functions of skeletal muscle, aside from producing movement?
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Which property of skeletal muscle refers to its ability to respond to stimuli?
Which property of skeletal muscle refers to its ability to respond to stimuli?
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What is the role of myofibrils within muscle cells?
What is the role of myofibrils within muscle cells?
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What does the term 'extensibility' refer to in the context of skeletal muscle?
What does the term 'extensibility' refer to in the context of skeletal muscle?
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Which component of skeletal muscle gives it a striated appearance?
Which component of skeletal muscle gives it a striated appearance?
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What does 'contractility' refer to in skeletal muscles?
What does 'contractility' refer to in skeletal muscles?
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In the case of a dislocated shoulder, which role of skeletal muscles is primarily compromised?
In the case of a dislocated shoulder, which role of skeletal muscles is primarily compromised?
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Which property of skeletal muscle allows it to return to its resting length after being stretched?
Which property of skeletal muscle allows it to return to its resting length after being stretched?
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What initiates the attachment of myosin heads to actin in muscle contraction?
What initiates the attachment of myosin heads to actin in muscle contraction?
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Which of the following describes the 'all-or-none' principle of muscle fiber contraction?
Which of the following describes the 'all-or-none' principle of muscle fiber contraction?
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How is energy provided for the sliding process during muscle contraction?
How is energy provided for the sliding process during muscle contraction?
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What occurs during the pivoting of the cross bridge in muscle contraction?
What occurs during the pivoting of the cross bridge in muscle contraction?
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What is one way that graded responses in skeletal muscle contraction can be achieved?
What is one way that graded responses in skeletal muscle contraction can be achieved?
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What happens to muscle fibers in a skeletal muscle during different intervals of stimulation?
What happens to muscle fibers in a skeletal muscle during different intervals of stimulation?
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What is the result of multiple cross bridges attaching and detaching during muscle contraction?
What is the result of multiple cross bridges attaching and detaching during muscle contraction?
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What is the significance of calcium ions in muscle contraction?
What is the significance of calcium ions in muscle contraction?
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What is the main role of a fixator muscle?
What is the main role of a fixator muscle?
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Which muscle group primarily produces extension at a joint?
Which muscle group primarily produces extension at a joint?
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What action do muscles crossing on the medial side of a joint produce?
What action do muscles crossing on the medial side of a joint produce?
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An example of a muscle that produces flexion is?
An example of a muscle that produces flexion is?
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Which of the following muscles is an antagonist to the pectoralis major?
Which of the following muscles is an antagonist to the pectoralis major?
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Which muscle action is produced by muscles that cross the lateral side of a joint?
Which muscle action is produced by muscles that cross the lateral side of a joint?
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In the context of muscle actions, what does a muscle crossing on the anterior side generally produce?
In the context of muscle actions, what does a muscle crossing on the anterior side generally produce?
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What is true about muscles crossing the knee and ankle joints in terms of their actions?
What is true about muscles crossing the knee and ankle joints in terms of their actions?
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Study Notes
Introduction
- Skeletal muscles require stimulation from motor neurons (nerve cells) to contract.
- A motor unit is one motor neuron and all the skeletal muscle cells it stimulates.
Muscle Types
- Skeletal muscles are surrounded and bundled by connective tissues—Endomysium surrounds individual muscle fibers Perimysium surrounds fascicles (bundles) of muscle fibers. Epimysium surrounds the entire skeletal muscle. Fascia is on the outside of the epimysium that blends with deep fascia.
- Skeletal, Cardiac, and Smooth muscles have different characteristics, structures, and functions; they are also grouped within the body by CT coverings,
- The epimysium of skeletal muscle blends with connective tissue attachment.
- Tendons are cordlike structures mostly made of collagen fibers.
- Aponeuroses are sheetlike structures of fibrous tissue.
Muscle Tissue Characteristics
- Irritability/Responsiveness: the ability to receive and respond to a stimulus.
- Contractility: the ability to forcibly shorten when stimulated.
- Extensibility: the ability to be stretched.
- Elasticity: the ability to recoil and resume resting length.
Microscopic Anatomy of Skeletal Muscle
- Sarcolemma: specialized plasma membrane.
- Myofibrils: long organelles inside muscle cells.
- Light (I) Bands and Dark (A) bands give the muscle its striated (banded) appearance and are important parts of the Sarcomere.
- Sarcoplasmic Reticulum (SR): specialized smooth endoplasmic reticulum that surrounds the myofibrils and stores and releases calcium.
Sarcomeres
- Contractile unit of skeletal muscle cells.
- Composed of thick (myosin) and thin (actin) filaments, organized in repeating units
- Thick filaments: composed of the protein myosin, ATPase enzymes to split ATP to release energy, and possess projections (myosin heads).
- Thin filaments: composed of the contractile protein actin, are anchored to the Z disc. At rest, the band lacks actin filaments called the H zone.
Muscle Contraction
- Sliding Filament Theory describes myosin heads pulling on actin filaments causing the muscle cell to shorten, requiring Ca2+ and ATP; with AP stopping Ca supply for the final step.
- Action potentials travel deep into the muscle fiber along membranous tubules (T-tubules), stimulating the SR to release Ca2+, triggering binding of myosin to actin, and initiating filament sliding. Contraction occurs and continues as long as calcium ions are available
- Cells return to their resting state; regulatory proteins returning to their resting shape, blocking myosin-binding sites.
Muscle Functions
- Skeletal muscle has three roles beyond movement: maintaining posture and body position, stabilizing joints, and generating heat.
Neuromuscular Junction
- Synapse: association site of the axon terminal, of the motor neuron and the sarcolemma of a muscle.
- Neurotransmitter: chemical released by nerves upon arrival of nerve impulses in the axon terminal.
- Acetylcholine (ACh): neurotransmitter that stimulates skeletal muscle.
- Synaptic cleft: gap between nerve and muscle filled with interstitial fluid.
Contraction of a Skeletal Muscle as a Whole
- Graded responses: different degrees of skeletal muscle shortening in response to different stimuli, by changing the frequency and number of muscle cells stimulated in one moment.
- Summation of contractions: as more action potentials occur and the muscle doesn't have time to completely relax between, the muscle will begin to have stronger force with each new contraction.
- Tetanus: if stimulation is very rapid, the muscle contractions will fuse into a smooth, sustained contraction.
- Muscle force depends on the number of fibers stimulated. When all motor units are active and stimulated, the muscle contraction is as strong as it can get.
Providing Energy for Muscle Contraction
- ATP is the primary source of energy for muscle contraction.
- Three pathways regenerate ATP: direct phosphorylation of ADP by creatine phosphate, aerobic respiration, and anaerobic glycolysis and lactic acid formation.
Muscle Fatigue and Oxygen Deficit
- If muscle activity is strenuous and prolonged, muscle fatigue occurs.
- Factors contributing to fatigue: ion imbalances, oxygen deficit, and lack of energy (ATP) supply, lactic acid accumulation.
- After exercise, the oxygen deficit is repaid by rapid, deep breathing to restore oxygen and ATP levels.
Types of Muscle Contractions
- Isotonic contractions: muscle shortens and movement occurs.
- Isometric contractions: muscle filaments try to slide, but the muscle is pitted against an immovable object, and tension increases but muscles do not shorten.
Muscle Tone
- State of continuous partial contractions of a muscle.
- Result of systematic stimulation of different motor units at different intervals
Effect of Exercise on Muscles
- Aerobic exercise results in stronger, more flexible muscles with greater resistance to fatigue, improved metabolism, and better functioning of the nervous system.
- Resistance exercise, like weightlifting, increases muscle size and strength. Individual muscle fibers enlarge.
Naming Skeletal Muscles
- Direction of muscle fibers (e.g., rectus).
- Relative size of muscle (e.g., maximus).
- Location of muscle (e.g., temporalis).
- Number of origins (e.g., triceps).
- Location of origin and insertion (e.g., sterno-cleido-mastoid).
- Shape of muscle (e.g., deltoid).
- Action of muscle (e.g., flexor, extensor).
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Description
Test your knowledge on muscle physiology, including types of muscles, their functions, and contractions. This quiz covers key concepts related to skeletal, cardiac, and smooth muscles, as well as their roles in movement. Prepare to challenge your understanding of muscle tone, isotonic and isometric contractions, and more.
