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Questions and Answers
What percentage of total body weight do skeletal muscles typically make up in males?
What percentage of total body weight do skeletal muscles typically make up in males?
Which property of muscle refers to its ability to respond to a stimulus?
Which property of muscle refers to its ability to respond to a stimulus?
Which of the following describes the ability of a muscle to shorten with force?
Which of the following describes the ability of a muscle to shorten with force?
What is the main characteristic that defines voluntary muscles?
What is the main characteristic that defines voluntary muscles?
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What property of muscle allows it to recoil to its original resting length after being stretched?
What property of muscle allows it to recoil to its original resting length after being stretched?
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What occurs when action potentials cease during muscle relaxation?
What occurs when action potentials cease during muscle relaxation?
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Which statement is true regarding motor units?
Which statement is true regarding motor units?
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How does the number of muscle fibers in a motor unit affect muscle control?
How does the number of muscle fibers in a motor unit affect muscle control?
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What is the relationship between motor unit recruitment and contraction strength?
What is the relationship between motor unit recruitment and contraction strength?
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Which type of muscles is likely to have more muscle fibers per motor unit?
Which type of muscles is likely to have more muscle fibers per motor unit?
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What type of muscle tissue is characterized by having multiple nuclei that are peripherally located and is under voluntary control?
What type of muscle tissue is characterized by having multiple nuclei that are peripherally located and is under voluntary control?
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Which muscle tissue type comprises the walls of hollow organs and blood vessels?
Which muscle tissue type comprises the walls of hollow organs and blood vessels?
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What structure in cardiac muscle facilitates communication between cells?
What structure in cardiac muscle facilitates communication between cells?
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What is the role of the autonomic nervous system in muscle tissue?
What is the role of the autonomic nervous system in muscle tissue?
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What is the primary structural unit of skeletal muscle?
What is the primary structural unit of skeletal muscle?
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Which connective tissue layer surrounds individual muscle fibers?
Which connective tissue layer surrounds individual muscle fibers?
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What characteristic distinguishes smooth muscle from other types of muscle?
What characteristic distinguishes smooth muscle from other types of muscle?
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What type of muscle is classified as involuntary and striated?
What type of muscle is classified as involuntary and striated?
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Which of the following is NOT a characteristic of muscle fibers?
Which of the following is NOT a characteristic of muscle fibers?
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What symbol represents the smallest functional unit of muscle contraction?
What symbol represents the smallest functional unit of muscle contraction?
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Which layer of connective tissue surrounds a bundle of muscle fibers known as a fascicle?
Which layer of connective tissue surrounds a bundle of muscle fibers known as a fascicle?
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What is the primary function of the sarcoplasmic reticulum in muscle cells?
What is the primary function of the sarcoplasmic reticulum in muscle cells?
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Which component is primarily responsible for the striated pattern seen in skeletal muscle?
Which component is primarily responsible for the striated pattern seen in skeletal muscle?
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How are muscle fibers adapted for their function?
How are muscle fibers adapted for their function?
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What is the role of satellite cells in muscle repair?
What is the role of satellite cells in muscle repair?
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Which type of muscle fibers typically experience reduced mass with aging?
Which type of muscle fibers typically experience reduced mass with aging?
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What happens to myostatin levels and satellite cell quantity with age?
What happens to myostatin levels and satellite cell quantity with age?
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What is the primary function of the agonist muscle during movement?
What is the primary function of the agonist muscle during movement?
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Which part of the muscle is referred to as the belly?
Which part of the muscle is referred to as the belly?
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In relation to muscle attachment, what is an origin?
In relation to muscle attachment, what is an origin?
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What is the function of myostatin?
What is the function of myostatin?
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What can endurance training help mitigate in aging individuals?
What can endurance training help mitigate in aging individuals?
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What defines the load in a lever system involving muscles?
What defines the load in a lever system involving muscles?
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Which of the following describes a muscle spasm?
Which of the following describes a muscle spasm?
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What is the primary role of myofibrils in muscle fibers?
What is the primary role of myofibrils in muscle fibers?
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Which structure corresponds to the light bands observed in skeletal muscle?
Which structure corresponds to the light bands observed in skeletal muscle?
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What causes the shortening of I bands during muscle contraction?
What causes the shortening of I bands during muscle contraction?
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What is the function of titin in muscle fibers?
What is the function of titin in muscle fibers?
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How do the A bands change during contraction according to the sliding filament theory?
How do the A bands change during contraction according to the sliding filament theory?
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What role does the troponin-tropomyosin system play in muscle contraction?
What role does the troponin-tropomyosin system play in muscle contraction?
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During muscle relaxation, how does tropomyosin affect the binding sites on actin?
During muscle relaxation, how does tropomyosin affect the binding sites on actin?
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What happens to crossbridge cycling when calcium ions are released into the muscle?
What happens to crossbridge cycling when calcium ions are released into the muscle?
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What is the H zone in skeletal muscle Anatomy?
What is the H zone in skeletal muscle Anatomy?
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What is the significance of the Z line within the sarcomere?
What is the significance of the Z line within the sarcomere?
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Which component is primarily responsible for the contraction of skeletal muscle fibers?
Which component is primarily responsible for the contraction of skeletal muscle fibers?
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What is the primary function of M lines in sarcomeres?
What is the primary function of M lines in sarcomeres?
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What is formed when ATP binds to myosin during the crossbridge cycle?
What is formed when ATP binds to myosin during the crossbridge cycle?
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What happens to the length of the sarcomere during muscle contraction?
What happens to the length of the sarcomere during muscle contraction?
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What is the main purpose of muscle tone in skeletal muscles?
What is the main purpose of muscle tone in skeletal muscles?
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What condition results in decreased muscle tone and flaccid muscles?
What condition results in decreased muscle tone and flaccid muscles?
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Which type of muscle fibers are considered slow-twitch?
Which type of muscle fibers are considered slow-twitch?
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What characterizes fast-twitch muscle fibers (Type IIX)?
What characterizes fast-twitch muscle fibers (Type IIX)?
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What happens to the reflexes during hypertonia?
What happens to the reflexes during hypertonia?
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Which statement is true regarding the role of the brain and spinal cord in muscle tone?
Which statement is true regarding the role of the brain and spinal cord in muscle tone?
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What distinguishes isometric contractions from isotonic contractions?
What distinguishes isometric contractions from isotonic contractions?
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What is a characteristic of type II A muscle fibers?
What is a characteristic of type II A muscle fibers?
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What effect does hypertonia have on muscle reflexes?
What effect does hypertonia have on muscle reflexes?
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What role do satellite cells play in skeletal muscles?
What role do satellite cells play in skeletal muscles?
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Which type of muscle contraction involves a change in muscle length while generating force?
Which type of muscle contraction involves a change in muscle length while generating force?
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What is the primary fiber type responsible for endurance activities?
What is the primary fiber type responsible for endurance activities?
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What distinguishes spastic paralysis from flaccid paralysis?
What distinguishes spastic paralysis from flaccid paralysis?
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In which type of muscle fibers would you find an abundance of mitochondria and rich capillary supply?
In which type of muscle fibers would you find an abundance of mitochondria and rich capillary supply?
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Which condition describes an increased muscle tone resulting in stiff and rigid muscle?
Which condition describes an increased muscle tone resulting in stiff and rigid muscle?
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Study Notes
Support and Movement 3: Muscular System
- Muscle is one of four basic tissue types in the human body
- Skeletal muscles comprise 40% of male body weight, about 32% of female body weight
- Muscle tissues perform a variety of functions
- Skeletal muscles are voluntary, controlled consciously via nervous system
- Cardiac and smooth muscles are involuntary, controlled by autonomic nervous system
Outline
- Skeletal Muscles Structure
- Mechanisms of Contraction
- Contractions of Skeletal Muscle
- Motor Unit
- Types of skeletal muscle
Properties of Muscle
- Contractility: Ability of muscle to shorten with force
- Excitability: Capacity of muscle to respond to a stimulus
- Extensibility: Muscle can be stretched to its normal resting length, and beyond, to a limited degree
- Elasticity: Ability of muscle to recoil to original resting length after stretched
Classification of Muscle
- Voluntary (skeletal): actions directed by thoughts via nervous system.
- Involuntary (cardiac and smooth): actions directed by autonomic nervous system
Types of Muscle Tissue
-
Skeletal muscle:
- Attached to bones
- Multiple, peripheral nuclei
- Striated, voluntary, and involuntary (reflexes)
-
Smooth muscle:
- Walls of hollow organs, vessels, glands, skin
- Single, central nuclei
- Not striated, involuntary, with gap junctions (visceral smooth)
-
Cardiac muscle:
- Heart
- Single, central nuclei
- Striated, involuntary, with intercalated disks
Skeletal Muscle Structure
- Most distinctive feature is striations and multinucleate nature
- Muscle fibers are muscle cells ensheathed by thin connective tissue (endomysium)
- The plasma membrane is called sarcolemma
- Muscle fibers are similar to other cells, but are multinucleate and striated
Skeletal Muscle Structure (Connective Tissue)
- Fibrous connective tissue from tendons forms sheaths (epimysium) that extend around and into muscle
- Inside the muscle, connective tissue divides muscle into columns called fascicles
- Connective tissue around fascicles is called perimysium
Skeletal Muscle Structure (Internal)
- Muscle fibers are muscle cells
- Ensheathed by thin connective tissue layer called endomysium
- Plasma membrane is called sarcolemma
- Muscle fibers are similar to other cells except are multinucleate and striated
Mechanisms of Contraction
- The sliding filament theory of muscle contraction describes how thin filaments (actin) slide past thick filaments (myosin), shortening the sarcomere.
- This process requires energy (ATP)
Structure of Muscle Fiber
- Each fiber contains myofibrils
- Myofibrils contain myofilaments (thick and thin filaments)
- Thick and thin filaments give rise to striations
Structure of Myofibril
- A band- is dark, corresponds to the length of thick filaments.
- I band- spans the distance between the A bands of successive sarcomeres
- H zone- light area in the center of A band where actin and myosin don't overlap
- Z disc- at center of I band where actins attach
Sarcomeres
- The contractile units in skeletal muscle.
- Structural elements are M lines (anchor myosin); titin attaches myosin to Z disc.
Sliding Filament Theory of Contraction
- Thin (actin) filaments slide over thick (myosin) filaments, shortening the sarcomere and producing muscle shortening.
- The lengths of the filaments do not change; the filaments slide past each other.
Cross-Bridge Cycle
- A series of steps demonstrating how ATP powers the movement of the myosin head relative to actin.
- The cycle involves cross-bridge attachment, myosin head pivoting, cross-bridge detachment, and myosin reactivation.
Control of Contraction
- Troponin-tropomyosin system controls cross-bridge attachment to actin.
- In relaxed muscle, tropomyosin blocks binding sites on actin.
Summary of the sliding filament theory of contraction
- A myofibril shortens by movement of the insertion toward the origin of the muscle.
- Sarcomere shortening is achieved by sliding of the myofilaments.
- Sliding of the filaments occurs via asynchronous myosin cross-bridge power strokes.
- Length of the filaments remains constant.
- A bands remain constant in length.
Excitation-Contraction Coupling (NMJ)
- Motor neuron ending at sarcolemma where a motor end plate (NMJ) occurs.
- ACh binds to receptors, triggering an action potential.
- Action potential propagates down T tubules opening calcium release channels
- Ca²+ activates the contraction mechanism
- Relaxation: Ca²+ pumped back into sarcoplasmic reticulum
Relationship of the Action Potential
- The action potential triggers an increase in intracellular Ca²+, leading to muscle contraction.
Muscle Relaxation
- Action potentials cease.
- Ca²+-ATPase pumps return Ca²⁺ into the SR.
- No more Ca²⁺ is available to bind to troponin C.
Motor Unit
- A motor neuron and all the muscle fibers it innervates.
- Number of muscle fibers per motor unit varies with degree of fine control.
- Contraction strength results from motor unit recruitment.
Muscle Tone
- Skeletal muscle exhibits muscle tone (tension) at rest.
- Involuntary contractions of motor units maintained by neurons in the brain and spinal cord.
- Important in maintaining posture and support
- Flaccid condition occurs when motor neurons are damaged or cut, reducing muscle tone
Muscle Tone Imbalance
- Hypotonia: decreased or lost muscle tone. Muscles loose, flattened.
- Hypertonia: increased muscle tone. Tendon reflexes and pathologic reflexes may occur, rigidity.
Types of Muscle Contractions
- Reflexive: involuntary
- Tonic: Maintenance of steady tension (muscle tone).
- Isometric: Muscle changes tension but not length.
-
Isotonic: Muscle changes length but not tension
- Concentric: Muscle shortens whilst generating force; muscle length decreases
- Eccentric: Muscle lengthens whilst generating force; muscle length increases.
Types of Skeletal Muscle
-
Type I (Slow oxidative):
- Adapted to contract slowly, without fatigue
- Utilizes mostly aerobic metabolism
- High in myoglobin content, rich capillary supply and many mitochondria
- Gives fibers red color
- Have small motor neurons
-
Type II (Fast glycolytic):
- Adapted to contract rapidly; fatigues quickly
- Utilizes mostly anaerobic metabolism
- Low in myoglobin content, poor capillary supply and few mitochondria
- Gives fibers white color
- Have larger motor units
-
Type IIA (Fast oxidative- glycolytic):
- Intermediate characteristics between Type I and Type IIX
Muscle Repair
- Skeletal muscles have stem cells (satellite cells) located near muscle fibers
- Satellite cells fuse to damaged muscle cells repair damage or fuse with each other to form new muscle fibers
- Myostatin inhibits satellite cells
Muscle Decline With Aging
- Reduced muscle mass (primarily type II fibers)
- Reduction in capillary blood supply
- Fewer satellite cells, increased myostatin production
Production of Movement by Muscles
- Muscle attachments include insertion and origin points; belly
- Biceps brachii is an example: origin, insertion, nerve supply, and actions
How Skeletal Muscles Produce Movements
- Lever system and leverage: rigid structures moving around fixed points (fulcrum)
- Effort causes movement, load opposes movement
Muscle Shapes
- Parallel, fusiform, parallel with tendinous bands, convergent, unipennate, bipennate, multipennate, and circular muscles.
Nomenclature (How muscles are named)
- Shape, Size, Location, Action, Attachment
Homeostatic Imbalance Disorders
-
Abnormal contractions
- Spasm: involuntary contraction of a single muscle → spasms in a group.
- Cramp: prolonged periods of muscle use, inadequate blood flow → painful
- Spasmodic twitching
- Tremor: rhythmic involuntary muscle movements
-
Exercise-induced muscle damage
- Delayed onset muscle soreness (DOMS), 12-48 hours after exercise, swelling, stiffness, accompanied by soreness, microscopic muscle damage
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Description
Test your knowledge on skeletal muscle physiology with this quiz. Questions cover topics like muscle properties, motor units, and muscle control mechanisms. Ideal for students studying human anatomy and physiology.
