Questions and Answers
What are body movements results from?
Alternating contraction and relaxation of muscles.
What is myology?
Scientific study of muscles.
What are the types of muscular tissue?
What is NOT a function of muscular tissue?
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What describes skeletal muscle tissue?
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Which muscle type is striated and involuntary?
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Each skeletal muscle is a separate organ composed of numerous cells called ____________.
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Match the following connective tissue components of skeletal muscle tissue:
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What is fibrosis?
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What happens during the sliding filament mechanism?
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What is the role of tropomyosin in muscle contraction?
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What does rigor mortis result from?
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What process begins with the SR releasing calcium ions?
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Which of the following is true about creatine phosphate?
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What does anaerobic respiration convert pyruvic acid to when oxygen levels are low?
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How long can anaerobic respiration provide enough energy for muscle activity?
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What is aerobic respiration primarily used for?
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What is produced when pyruvic acid enters the mitochondria during aerobic respiration? (Select all that apply)
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How many molecules of ATP are produced from one glucose molecule during aerobic respiration?
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What two sources of oxygen does muscle tissue utilize?
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What contributes to muscle fatigue?
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What is recovery oxygen uptake?
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What factors affect maximum muscle tension? (Select all that apply)
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What is a twitch contraction?
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What is the latent period in muscle contraction?
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During the contraction period, what binds to troponin?
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What occurs during the relaxation period of muscle contraction?
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What is the refractory period?
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What is muscle tone?
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What are the two types of muscle contractions? (Select all that apply)
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How do muscle fibers vary in content?
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What are the three main types of muscle fibers?
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What characteristics define slow oxidative fibers?
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What are fast glycolytic fibers known for?
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How can exercise affect muscle fiber composition?
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What is the principal tissue of the heart wall?
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What distinguishes cardiac muscle from skeletal muscle?
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What are the characteristics of smooth muscle tissue?
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How does aging affect skeletal muscle?
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Study Notes
Body Movements & Myology
- Body movements arise from muscle contractions, involving alternating cycles of shortening and relaxing of muscles.
- Myology is the scientific study dedicated to muscles.
Types of Muscular Tissue
- Three primary types exist: skeletal, cardiac, and smooth muscle.
Functions of Muscular Tissue
- Produces body movements, stabilizes body positions, facilitates movement of substances within the body, and generates heat.
Key Properties of Muscle Tissue
- Excitability: Ability to respond to stimuli and generate electrical signals.
- Contractility: Muscle tissue can shorten and thicken, exerting force.
- Extensibility: Muscle can be stretched without damage.
- Elasticity: Muscles return to their original shape post-contraction or extension.
Characteristics of Skeletal Muscle
- Composed of long cylindrical fibers with multiple nuclei, striated appearance due to light and dark bands, operates primarily under voluntary control with some subconscious regulation.
Characteristics of Cardiac Muscle
- Found only in the heart, with branched fibers and intercalated discs; contractions are involuntary and regulated by pacemaker tissue, exhibiting autorhythmicity.
Characteristics of Smooth Muscle
- Located in the walls of hollow organs (e.g., blood vessels, airways), non-striated with a single central nucleus, primarily involuntary.
Muscle Fibers
- Each skeletal muscle is made up of elongated muscle cells called fibers, which cannot divide post-fusion, leading to a predetermined number of fibers at birth.
Connective Tissue in Skeletal Muscle
- Comprises several layers: fascia (superficial and deep), epimysium, perimysium, endomysium, tendons, and aponeurosis.
Types of Fascia
- Superficial Fascia: Separates muscle from skin, containing areolar and adipose tissues for insulation and protection.
- Deep Fascia: Surrounds muscles, holds similar functions together, and allows free movement while supplying nerves and blood vessels.
Muscle Fiber Components
- Tendon: Connective tissue extending beyond muscle fibers, attaching muscles to bones.
- Aponeurosis: A broad, flattened tendon.
Somatic Motor Neurons
- Neurons that stimulate skeletal muscle contraction, with axons extending from the brain or spinal cord to muscle fibers.
Blood Capillaries
- Supply oxygen and nutrients while removing waste products generated by muscle metabolism.
Microscopic Anatomy of Skeletal Muscle
- Involves structures like myoblasts, sarcolemma, T-tubules, myofibrils, and sarcoplasmic reticulum, essential for muscle function and contraction.
Muscle Growth
- Hypertrophy refers to the enlargement of existing muscle fibers, while hyperplasia refers to the increase in the number of muscle fibers, stimulated by hormones like testosterone.
Sliding Filament Mechanism
- Myosin heads walk along thin filaments, pulling them toward the sarcomere's center, shortening the muscle.
Contraction Cycle Steps
- Involves steps like ATP hydrolysis, cross-bridge formation, power stroke, and myosin detachment, repeating as long as ATP and calcium are available.
Excitation-Contraction Coupling
- An increase in calcium ion levels triggers muscle contraction; a decrease stops it, with calcium pumps returning calcium to the sarcoplasmic reticulum.
Rigor Mortis
- Occurs post-death due to ATP depletion, causing myosin-actin cross-bridges to remain connected.
Length-Tension Relationship
- The strength of contraction is influenced by the sarcomere length pre-contraction, with optimal overlap necessary for forceful contractions.
Neuromuscular Junction Details
- The synapse between motor neurons and muscle fibers includes neurotransmitter release, receptor activation, and propagation of action potentials.
Muscle Metabolism
- ATP production in muscle fibers is crucial for contraction cycles, involving creatine phosphate, anaerobic and aerobic respiration, with adequate oxygen necessary for lengthy activities.
Creatine Phosphate Role
- A high-energy molecule synthesized from excess ATP, which rapidly regenerates ATP during initial muscle activity (approximately 15 seconds).
Anaerobic and Aerobic Respiration
- Anaerobic respiration generates ATP without oxygen, producing lactic acid as a byproduct, while aerobic respiration occurs using oxygen to completely oxidize pyruvic acid, yielding substantial ATP.### Oxygen and Muscle Metabolism
- Myoglobin and hemoglobin are both oxygen-binding proteins; myoglobin specifically releases oxygen in muscle cells.
- Aerobic respiration provides over 90% of ATP for activities lasting longer than 10 minutes, essential for prolonged effort.
Muscle Fatigue
- Muscle fatigue is characterized by the inability to maintain contraction after extended activity.
- Contributing factors include:
- Inadequate calcium ion release from the sarcoplasmic reticulum (SR).
- Depletion of creatine phosphate.
- Low oxygen levels.
- Decreased glycogen and nutrient availability.
- Buildup of lactic acid and adenosine diphosphate (ADP).
- Insufficient acetylcholine release by motor neurons.
Control of Muscle Tension
- Muscle tension varies based on multiple factors:
- Rate of nerve impulse arrival.
- Pre-contraction stretch amount.
- Availability of nutrients and oxygen.
- Size of the motor unit.
Motor Units
- A motor unit includes one motor neuron and the muscle fibers it regulates.
- Each motor neuron interfaces with around 150 muscle fibers.
- Fine movements are controlled by small motor units, while larger muscles have larger motor units.
- Examples of muscle fiber count per motor unit:
- Voice production: 2-3 fibers.
- Eye movements: 10-20 fibers.
- Arm and leg muscles: 2000-3000 fibers.
Twitch Contraction
- Twitch contraction is a brief muscle fiber response to an action potential, lasting from 20 to 200 milliseconds.
Muscle Contraction Phases
- Latent Period: A delay of about 2 milliseconds between stimulus and contraction as action potentials spread and calcium is released.
- Contraction Period: Calcium binds to troponin, exposing myosin-binding sites on actin; lasts 10-100 milliseconds.
- Relaxation Period: Calcium is reabsorbed into the SR, covering binding sites and allowing muscle relaxation, ranging from 10 ms (eye muscles) to 100 ms (leg muscles).
- Refractory Period: A phase post-contraction where fibers cannot respond to action potentials; 5 ms for skeletal muscles, 300 ms for cardiac muscles.
Muscle Tone
- Muscle tone refers to slight tension in muscles, maintaining firmness through weak contractions of motor units.
- Alternating activation of small motor units sustains muscle tone, preventing head droop.
Types of Contractions
- Isotonic: Tension stays constant while muscle length changes, like lifting an object.
- Isometric: Muscle length remains unchanged while tension increases, like holding an object steady.
Muscle Fiber Content
- Muscle fibers differ in myoglobin content:
- Red fibers: High myoglobin, dark in color, more mitochondria, and better blood supply.
- White fibers: Low myoglobin, lighter in color.
Three Main Types of Muscle Fibers
- Classified by contraction speed and fatigue resistance:
- Slow Oxidative (SO): Smallest, dark red, highly resistant to fatigue, suited for endurance.
- Fast Oxidative-Glycolytic (FOG): Intermediate size and resistance, good for walking and sprinting.
- Fast Glycolytic (FG): Largest, low myoglobin, quick fatigue, optimal for intense, short bursts of activity.
Distribution of Muscle Fiber Types
- Muscle fiber composition varies by activity type, genetic factors, and training:
- Postural muscles are primarily slow oxidative.
- Upper body muscles use more FG fibers for quick, strong movements.
- Leg muscles have mixed SO and FOG fibers for support and locomotion.
Exercise Impact on Muscle Tissue
- Genetic predispositions affect the ratio of FG to SO fibers.
- Aerobic exercise can convert some FG fibers to FOG fibers, improving endurance without significant muscle mass increase.
- Strength training can increase FG fiber size through hypertrophy.
Cardiac Muscle Tissue
- Found in the heart wall, characterized by mononucleation, striations, and a rich supply of mitochondria.
- Relies on aerobic respiration for ATP, using lactic acid from skeletal muscles.
Cardiac Muscle Structure
- Intercalated discs connect cardiac fibers, allowing for synchronized contractions.
- Cardiac tissue is autorhythmic, leading to continuous, rhythmic contractions lasting longer than skeletal muscle twitch.
Smooth Muscle Tissue
- Typically involuntary, found in walls of hollow organs, blood vessels, and airways.
- Fibers communicate via gap junctions and can respond to neurotransmitters and hormones.
Smooth Muscle Anatomy
- Lacks regular striations and sarcomeres; instead, filaments attach to dense bodies.
- Contains a small amount of stored calcium, leading to prolonged contraction duration.
Smooth Muscle Physiology
- Contractions are slower, lasting longer than skeletal muscle contractions, with calcium trigger responses.
- Can sustain muscle tone, crucial for maintaining pressure in various bodily systems.
Regeneration of Muscle Tissue
- Skeletal muscle has limited regenerative capacity, mainly through hypertrophy.
- Cardiac muscle can enlarge in response to increased workload, whereas smooth muscle can still divide.
Muscle Development
- Muscles originate from mesoderm, which organizes into somites during embryonic development.
- Somite cells differentiate into myotome (skeletal muscle), dermatome (connective tissue), and sclerotome (vertebrae).
Aging and Muscular Tissue
- Aging leads to a decline in skeletal muscle mass, strength, reflex speed, and flexibility.
- An increase in slow oxidative fibers may occur with age.
- Participating in aerobic and strength training can mitigate muscle performance decline.
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