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Questions and Answers
What is the role of the antagonist muscle in skeletal movement?
What is the role of the antagonist muscle in skeletal movement?
What triggers skeletal muscle excitation?
What triggers skeletal muscle excitation?
Which structure is the smallest functional unit of skeletal muscle?
Which structure is the smallest functional unit of skeletal muscle?
What function do motor neurons serve in muscle movement?
What function do motor neurons serve in muscle movement?
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In the sliding filament model, which process occurs during muscle contraction?
In the sliding filament model, which process occurs during muscle contraction?
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What percentage of total body mass do skeletal muscles constitute?
What percentage of total body mass do skeletal muscles constitute?
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Which skeletal muscle shape is characterized by fibers arranged in a diagonal direction onto a tendon?
Which skeletal muscle shape is characterized by fibers arranged in a diagonal direction onto a tendon?
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What is the primary function of skeletal muscles?
What is the primary function of skeletal muscles?
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Which connective tissue layer surrounds the entire skeletal muscle?
Which connective tissue layer surrounds the entire skeletal muscle?
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Which term describes muscles that are under voluntary control?
Which term describes muscles that are under voluntary control?
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In which skeletal muscle shape do fibers run parallel to each other?
In which skeletal muscle shape do fibers run parallel to each other?
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Which of the following types of skeletal muscle has fibers arranged in multiple rows of diagonal orientation?
Which of the following types of skeletal muscle has fibers arranged in multiple rows of diagonal orientation?
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What type of muscle contains the perimysium layer that surrounds fascicles?
What type of muscle contains the perimysium layer that surrounds fascicles?
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Which type of skeletal muscle fiber is primarily associated with high fatigue resistance?
Which type of skeletal muscle fiber is primarily associated with high fatigue resistance?
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What is the primary energy regeneration method for Type IIB skeletal muscle fibers?
What is the primary energy regeneration method for Type IIB skeletal muscle fibers?
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What occurs when a motor neuron stops releasing ACh at the neuromuscular junction?
What occurs when a motor neuron stops releasing ACh at the neuromuscular junction?
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Which of the following characteristics is true for Type IIA muscle fibers?
Which of the following characteristics is true for Type IIA muscle fibers?
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Which physiological function is primarily served by muscle tone?
Which physiological function is primarily served by muscle tone?
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Which condition is characterized by a state of continuous muscle contraction due to ATP depletion?
Which condition is characterized by a state of continuous muscle contraction due to ATP depletion?
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Which muscle fiber type is known for having low fatigue resistance?
Which muscle fiber type is known for having low fatigue resistance?
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What is the main source of energy for Type I skeletal muscle fibers?
What is the main source of energy for Type I skeletal muscle fibers?
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Study Notes
Skeletal Muscle Overview
- Skeletal muscles are attached to bones by tendons
- They produce body movements relative to each other
- They are voluntary, meaning you control when and how they work
- The majority of muscles in the body are skeletal
- They make up 30-40% of total body mass
- Composed of integrated tissues: skeletal muscle fibers, blood vessels, nerve fibers, and connective tissue
Behavioral Goals
- Define skeletal muscle
- Illustrate skeletal muscle function
- Classify skeletal muscles by shape
- Relate skeletal muscle facts to pathological conditions
- Describe skeletal muscle structure
- Explain skeletal muscle contraction mechanism
- Explain energy source consumption
- Discuss muscle conditions (contracture, fatigue, and tone)
Muscle Functions
- Body movement (e.g., limb movement)
- Maintaining body position (e.g., erector spinae)
- Supporting internal organs (e.g., pelvic diaphragm)
- Regulating materials (e.g., sphincters of the digestive tract)
- Temperature regulation
Muscle Origins and Insertions
- Origin: bony attachment at the stationary end of the muscle
- Belly: the thicker, middle region of the muscle between origin and insertion
- Insertion: bony attachment to the mobile end of the muscle
Skeletal Muscle Shapes
- Circular: surrounding openings (e.g., orbicularis oris)
- Convergent: wider origin, narrower insertion (e.g., pectoralis major)
- Parallel: fibers parallel to each other (e.g., sartorius)
- Fusiform: spindle-shaped, wider belly (e.g., biceps brachii)
- Unipennate: fibers arranged diagonally to a tendon (e.g., extensor digitorum longus)
- Bipennate: two rows of fibers facing opposite directions (e.g., rectus femoris)
- Multipennate: multiple rows of fibers converging on multiple tendons (e.g., deltoid)
Skeletal Muscle Structure
- Epimysium: outer connective tissue layer surrounding the entire muscle
- Perimysium: surrounds bundles of muscle fibers (fascicles)
- Endomysium: surrounds individual muscle fibers
- Fascicle: bundle of muscle fibers
- Sarcolemma: muscle fiber membrane
- Sarcoplasm: cytoplasm of the muscle fiber
- Sarcomere: smallest contractile unit of a muscle fiber
- Myofibrils: thread-like protein filaments within the muscle fiber
- Myofilaments: actin and myosin filaments within myofibrils
Skeletal Muscle Movement
- Prime mover: muscle primarily responsible for a movement
- Antagonist: muscle that opposes the prime mover
- Synergist: muscle that assists the prime mover
Ordinary Body Movements
- Flexion: bending a joint
- Extension: straightening a joint
- Rotation: turning a joint
- Abduction: moving a limb away from the midline
- Adduction: moving a limb toward the midline
- Circumduction: circular movement of a limb
How Skeletal Muscles Move
- Sensory neurons: detect stimuli and transmit signals to the central nervous system
- Motor neurons: carry signals from the central nervous system to muscles to cause movement
Neuromuscular Junction
- Synaptic connection between a motor neuron and a muscle fiber
- Site for action potential transmission from nerve to muscle
Skeletal Muscle Excitation
- Triggered by signaling from the nervous system at the neuromuscular junction
- Acetylcholine (ACh) diffuses across the synaptic cleft
- ACh binds to ACh receptors within the sarcolemma
- Sodium (Na+) ions enter the muscle fiber, depolarizing the membrane
- Calcium (Ca++) is released from the sarcoplasmic reticulum
Skeletal Muscle Contraction (Cross-Bridge)
- Myosin heads split ATP and become reoriented
- Myosin heads bind to actin, forming cross-bridges
- Myosin heads rotate, pulling actin filaments
- ATP binds to myosin, detaching it from actin
Sliding Filament Model of Contraction
- Thin filaments (actin) are pulled past thick filaments (myosin)
- Sarcomeres shorten, leading to muscle contraction
Providing Energy for Contraction
- Direct phosphorylation: creatine phosphate (CP) to ADP
- Anaerobic mechanism: glycolysis and lactic acid formation
- Aerobic mechanism: oxidative phosphorylation
Types of Skeletal Muscle Fibers
- Type I (slow oxidative): slow contraction, high resistance to fatigue, aerobic metabolism, red color
- Type IIA (fast oxidative-glycolytic): fast contraction, moderate resistance to fatigue, aerobic and anaerobic metabolism, red color
- Type IIB (fast glycolytic): fast contraction, low resistance to fatigue, anaerobic metabolism, white color
Muscle Relaxation
- Motor neuron stops releasing ACh
- Muscle fiber repolarizes
- Calcium (Ca++) is actively transported back into the sarcoplasmic reticulum
- Actin-binding sites are shielded
- Loss of ability to form cross-bridges
Muscle Tone
- Slight, ongoing muscle contraction even when not actively moving
- Maintains posture and stabilizes joints
Muscle Contracture
- Continuous muscle contraction due to ATP depletion
- Actin filaments fail to detach from myosin heads
Muscle Fatigue
- Depletion of ATP or glycogen
- Blood interruption
- Reduced oxygen levels
- Impaired signaling from nerves to muscles
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Description
Test your knowledge of skeletal muscles, their functions, and structures in this comprehensive quiz. Explore topics such as muscle classification, contraction mechanisms, and related pathological conditions. Perfect for students learning about human anatomy and physiology.
