Questions and Answers
What are concentric contractions?
Isotonic contractions in which muscle shortens and does work like picking up a book.
What are eccentric contractions?
Isotonic contractions in which muscle generates force as it lengthens.
What does isometric mean in muscle contraction?
No movement; no shortening of muscle; cannot move a load.
What is muscle tone?
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What role does phosphorylation play in muscle contraction?
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What is Anaerobic Respiration?
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What occurs during Aerobic Respiration?
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What leads to muscle fatigue?
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What are the requirements for the resting state of muscles?
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What factors determine the force of muscle contraction?
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What characterizes slow oxidative fibers?
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What are fast glycolytic fibers?
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What happens during aerobic exercise?
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What is disuse atrophy?
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What is peristalsis?
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What are varicosities in smooth muscle?
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Describe the NMJ of smooth muscle.
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What does the sarcoplasmic reticulum of smooth muscle lack?
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What characterizes smooth muscle contraction?
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How is smooth muscle contraction regulated?
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What is the definition of excitability?
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What does contractibility mean?
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Define extensibility.
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What is meant by elasticity in muscle tissue?
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Which of the following describes smooth muscle?
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What characterizes cardiac muscle?
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What are the main functions of muscle tissue?
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What is the composition of skeletal muscle?
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Define direct attachment of muscle.
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What is an indirect attachment of muscle?
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What is a tendon?
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What is an aponeurosis?
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What does the term 'origin' refer to in muscle attachment?
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Define epimysium.
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What is the function of the perimysium?
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Describe the endomysium.
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What is a fascicle?
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What does sarcolemma refer to?
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Define sarcoplasm.
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What are myofibrils?
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What are glycosomes?
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What is the function of the sarcoplasmic reticulum?
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Describe the H Zone.
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What does the M Line represent?
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What is a Z disc?
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Define sarcomere.
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What are myofilaments?
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What are thick filaments primarily composed of?
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What are thin filaments primarily composed of?
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What are intermediate (desmin) filaments?
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What is the composition of myofilaments?
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Describe myosin's structure.
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What happens during a cross bridge formation?
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What does actin provide in muscle cells?
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Define regulatory proteins in thin filaments.
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What does the elastic filament do?
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What is the function of T Tubule?
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What does the Z line signify?
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What is the A band?
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What is the I band?
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What does the sliding filament theory describe?
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What is the neuromuscular junction?
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What is required for skeletal muscle fiber contraction?
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What are synaptic vesicles?
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Describe the neuromuscular junction process.
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What is excitation-contraction coupling?
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Define power stroke.
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What happens during muscle recovery?
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What is a twitch?
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What is a graded muscle response?
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What is wave or temporal summation?
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Define unfused or incomplete tetanus.
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What is complete tetanus?
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What does treppe refer to?
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What is isotonic contraction?
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Study Notes
Muscle Tissue Characteristics
- Excitability: Muscle tissue can respond to stimuli, primarily nervous impulses.
- Contractibility: Muscles can shorten and thicken when stimulated.
- Extensibility: Muscles have the ability to stretch beyond their normal length.
- Elasticity: Muscles can return to their original shape and size after being stretched or contracted.
Types of Muscle
- Smooth Muscle: Involuntary muscle found in the walls of hollow organs; elongated cells without striations.
- Cardiac Muscle: Striated, branched muscle with intercalated disks; it is involuntary.
- Skeletal Muscle: Long, striated muscle cells arranged in parallel; voluntary and multinucleated.
Functions of Muscle Tissue
- Movement and locomotion
- Maintaining posture
- Stabilizing joints
- Generating heat through muscle activity
Structure of Skeletal Muscle
- Composed of muscle fibers, blood vessels, nerve fibers, and connective tissue. Requires continuous oxygen and nutrient delivery.
- Direct Attachment: Epimysium of muscle fuses with the periosteum of bone or perichondrium of cartilage.
- Indirect Attachment: Tendons connect muscle to bone, extending beyond the muscle.
- Tendons: Rope-like extensions of connective tissue, while Aponeurosis is a flat sheet-like structure.
Connective Tissue Sheaths
- Epimysium: Dense connective tissue surrounding the entire muscle.
- Perimysium and Fascicles: Fascicles are bundles of muscle fibers wrapped in perimysium.
- Endomysium: Wispy connective tissue sheath surrounding individual muscle fibers.
Muscle Fiber Components
- Sarcolemma: Plasma membrane of a muscle cell.
- Sarcoplasm: Cytoplasm containing glycosomes (glycogen storage) and myoglobin (oxygen storage).
- Myofibrils: Rod-like structures that account for muscle cell volume, containing sarcomeres (contractile units) and myofilaments.
Myofilaments
- Thick Filaments: Composed of myosin, extending the entire length of the A band.
- Thin Filaments: Consists of actin, extending across the I band.
- Cross Bridge: Myosin heads link thick and thin filaments during contraction.
Sarcomere Structure
- Z Disc: Midline interruption of I band; connects thin filaments.
- H Zone: Lighter region in the A band, bisected by the M line.
- Sliding Filament Theory: Thin filaments slide over thick filaments during contraction, shortening the muscle.
Excitation-Contraction Coupling
- Action potential generation leads to muscle contraction through calcium release from the sarcoplasmic reticulum.
- Calcium binds to troponin, allowing myosin heads to attach to actin for contraction.
Muscle Contraction Types
- Twitch: Rapid, jerky response; a single contraction follows a single stimulus.
- Graded Muscle Response: Variations in muscle movement strength, influenced by stimulus frequency and intensity.
- Wave Summation: Successive stimuli cause a stronger contraction due to incomplete relaxation.
- Tetanus: Sustained muscle contraction occurs when stimuli frequency increases.
Muscle Contraction Energy Sources
- Aerobic Respiration: Generates high ATP through glycolysis and complete breakdown in mitochondria; requires continuous oxygen.
- Anaerobic Respiration: Glycolysis leads to lactic acid accumulation in the absence of oxygen; generates less ATP quickly.
- Phosphorylation: Creatine phosphate supplies phosphate to regenerate ATP quickly for short-term energy.
Muscle Fatigue and Recovery
- Fatigue: Occurs when ATP usage exceeds production, leading to lactic acid buildup and ionic imbalances.
- Recovery: Requires replenishing oxygen, converting lactic acid, resynthesizing glycogen, ATP, and creatine phosphate.
Muscle Characteristics
- Muscle Tone: Even at rest, muscles maintain slight tension to stabilize joints and posture.
- The force of muscle contractions depends on the number of crossbridges, stimulated fibers, fiber sizes, and stimulation frequency.### Muscle Physiology Basics
- Muscle contraction strength increases with the number of stimulated fibers.
- Larger muscle fibers generate stronger contractions, influenced by training and genetics.
- Muscle fiber size can be modified through exercise, though individuals are born with a predetermined number of fibers.
- Faster stimulation leads to stronger muscle contractions until optimal stretch is reached; excessive stretching hinders contraction.
- Optimal overlap of thick and thin filaments (A) ensures effective contraction, while partial overlap (B) still allows for some contraction.
Muscle Fiber Types
-
Slow Oxidative Fibers
- Contract slowly, utilize aerobic pathways for ATP production, high endurance, and rich in mitochondria.
- Resilient to fatigue but have less power due to slower ATPase activity.
-
Fast Oxidative Fibers
- Contract rapidly, also use aerobic pathways, resistant to fatigue.
- Characteristics include a rich supply of myoglobin and capillaries, allowing for quick ATP production.
-
Fast Glycolytic Fibers
- Rely on anaerobic pathways, produce less ATP quickly, and tire rapidly.
- Characterized by large diameter and minimal mitochondria; suited for brief, intense activities.
Exercise Effects on Muscle
-
Aerobic Exercise
- Increases mitochondrial numbers and myoglobin synthesis in muscle fibers.
- Primarily enhances slow oxidative fibers, contributing to endurance through angiogenesis (new capillary formation).
-
Resistance Exercise
- Focuses on anaerobic pathways and intensively loads muscles.
- More significantly increases muscle fiber size than aerobic exercise, promoting hypertrophy.
- Can convert some fast oxidative fibers to fast glycolytic fibers.
Muscle Atrophy
- Disuse atrophy occurs when muscles weaken and shrink due to inactivity.
- Prolonged disuse can lead to muscle tissue converting to fibrous connective tissue.
Smooth Muscle Structure
- Smooth muscle fibers are smaller than skeletal fibers and lack connective tissue sheaths except for the endomysium.
- Organized in layers: longitudinal for dilation and circular for constriction of tubes.
- Features no motor end plates or structured neuromuscular junctions; uses varicosities to release neurotransmitters.
Smooth Muscle Physiology
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Peristalsis
- Smooth muscle layers contract and relax alternately, propelling contents through organ lumens.
-
Varicosities
- Enlarged nerve fibers release neurotransmitters into synaptic clefts during smooth muscle activation.
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Sarcoplasmic Reticulum
- Lacks sarcomeres and T-tubules; instead, features caveoli for calcium concentration.
- Myofilaments consist of both thick and thin components, arranged diagonally, and lack troponin.
Smooth Muscle Contraction
- Triggered by neurotransmitter-induced action potentials that release calcium.
- Calcium interacts with calmodulin, activating myosin light chain kinase to facilitate muscle contraction.
- Involves calcium influx from both caveoli and extracellular space, leading to myosin activation and fiber shortening.
Regulation of Smooth Muscle Activity
- Controlled by autonomic nerve neurotransmitters causing excitation or inhibition.
- Influenced by chemical factors, such as oxytocin in labor and histamine during inflammation.
- Somatic motor neurons release solely acetylcholine as a neurotransmitter.
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Description
Explore key concepts from Chapter 9 of Human Anatomy and Physiology with these flashcards. Each card provides essential definitions of important terms, including excitability, contractibility, extensibility, and elasticity. Master these concepts for a deeper understanding of muscle function.