Chapter 3: Myology
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Learning Objectives
• Compare and contrast the three types of muscle tissue in the
human body.
• Discuss the five functions of skeletal muscle.
• Compare and contrast parallel and pennate fiber arrangements
and give an example of each.
• Identify the six factors that make up muscle names. Give
examples using each factor.
• Explain the contribution of each of the five properties of
skeletal muscle tissue to human movement.
• Identify the major macroscopic and microscopic structures of
muscle tissue and describe the function of each.
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Learning Objectives (cont’d)
• List the events that lead to a skeletal muscle contraction and
identify all chemicals necessary in the process.
• Discuss the factors that influence the amount of force produced
by a muscle.
• Compare and contrast slow twitch, fast twitch, and
intermediate muscles fibers.
• Compare and contrast isometric and isotonic muscle
contractions.
• Compare and contrast concentric and eccentric muscles
contractions.
• Discuss the functional interrelationships between agonist,
synergist, and antagonist muscles.
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Learning Objectives (cont’d)
• Identify the major skeletal muscles of the human body.
• Identify the components of a lever and give an example of
each type of lever in the human body.
• Identify and describe the anatomical structures of
proprioception in the human body.
• Define and demonstrate active, passive, and resisted range of
motion.
• Explain the purpose of performing active, passive, and resisted
range of motion.
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Types of Muscle Tissue
• Smooth Muscle (involuntary)
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In walls of hollow organs, vessels, & respiratory passageways;
functions in digestion, reproduction, circulation, & breathing
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Has no striations (visible alternating dark & light fibers)
• Cardiac Muscle (involuntary)
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Makes up wall of heart; creates pulsing action to circulate blood
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Unique in that electrical impulse travels from cell to cell
• Skeletal Muscle (voluntary)
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Connected to bones; produces movement at joints
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Types of Muscle Tissue (cont’d)
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Skeletal Muscle Functions
• Motion: Primary function is to exert pull on bones,
creating motion
• Posture: Maintain upright posture against gravity
• Protection: Protect underlying structures in areas where
bones do not
• Thermogenesis: Produce body heat
• Vascular Pump: Help propel circulation of lymph &
venous blood via contractions of skeletal muscles
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Fiber Direction and Naming Muscles
• Parallel Arrangements
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Fibers equal in length that do not intersect
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Enables entire muscle to shorten equally & in same direction;
maximizes range of motion
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Fusiform: thick central belly with tapered ends (brachialis,
biceps brachii)
–
Circular: fiber arrangements surround an opening to form a
sphincter; designed to contract & close passages or relax & open
them (orbicularis oris, sphincter ani)
–
Triangular: broad at base, converging to single point; fanshaped arrangement allows diverse actions (pectoralis major,
trapezius)
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Fiber Direction and Naming Muscles
(cont’d)
• Pennate Arrangements
–
Feather-shaped, with shorter fibers intersecting a central tendon
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Maximize number of fibers in an area, cross-sectional area, &
force production
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Unipennate: Fibers run obliquely from one side of central
tendon; look like half a feather (tibialis posterior, biceps femoris)
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Bipennate: Fibers run obliquely along both sides of central
tendon; look like a full feather (rectus femoris)
–
Multipennate: Multiple tendons with oblique muscle fibers on
both sides; produce least amount of force (deltoid)
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Fiber Direction and Naming Muscles
(cont’d)
• Naming Muscles
–
Fiber Direction
• Oblique (slanting): external oblique
• Rectus (straight): rectus abdominis
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Location
• Brachii (arm): biceps brachii
• Femoris (thigh): rectus femoris
• Pectoralis (chest): pectoralis major
• Abdominus (abdomen): rectus abdominus
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Fiber Direction and Naming Muscles
(cont’d)
• Naming Muscles
–
Action
• Flexor: flexor carpi radialis
• Extensor: extensor digitorum
• Pronator: pronator teres
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Size
• Major/minor: pectoralis major & minor
• Maximus/medius/minimus: gluteus maximus, etc.
• Longus/brevis/tertius: peroneus longus, etc.
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Fiber Direction and Naming Muscles
(cont’d)
• Naming Muscles
–
Shape
• Trapezoid: trapezius
• Delta: deltoid
• Saw-shaped: serratus anterior
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Number of Heads
• Biceps (2 heads): biceps brachii
• Triceps (3 heads): triceps brachii
• Quadriceps (4 heads): quadriceps (4 anterior thigh muscles)
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Skeletal Muscle Properties
• Extensibility
–
Ability to stretch without sustaining damage
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Allows muscles to lengthen when relaxed
• Elasticity
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Ability to return to original shape after lengthening or
shortening
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Maintains a specific shape & geometry in muscles despite
malleable nature
• Excitability
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Ability to respond to a stimulus by producing electrical signals
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Allows muscle to contract & function
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Skeletal Muscle Properties (cont’d)
• Conductivity
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Ability to propagate electrical signals, including action potentials
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Allows action potential to be transmitted along muscle cell,
activating tissue & initiating muscle contraction
• Contractility
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Ability to shorten & thicken, thus producing force, in response to
a specific stimulus
–
Allows force production & movement
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Anatomy of Skeletal Muscle Tissue
• Macroscopic Anatomy
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Connective tissue wrappings support, protect, & separate
portions of muscle & whole muscles
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Fibers: individual muscle cells
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Endomysium: sheath of connective tissue enveloping fibers
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Fascicles: bundles of grouped muscle fibers
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Perimysium: layer of connective tissue enveloping fascicles
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Epimysium: layer of deep fascia enveloping bundle of fascicles
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Musculotendinous junction: point where epimysium
converges to form a tendon
–
Muscle belly: portion of muscle between tendons
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Anatomy of Skeletal Muscle Tissue
(cont’d)
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Anatomy of Skeletal Muscle Tissue
(cont’d)
• Microscopic Anatomy
–
Sarcolemma: cell membrane; regulates chemical transport into
& out of fiber
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Sarcoplasm: a gelatinous substance surrounding structures
within fiber; cytoplasm of muscle cells
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Nuclei: structures within a fiber that contain functional
information for cell & control its operations
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Myofibrils: specialized contractile proteins that make skeletal
muscle tissue appear striated; two filaments: thin & thick
–
Sarcomere: functional unit of muscle fiber; their shortening
causes contraction
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Anatomy of Skeletal Muscle Tissue
(cont’d)
• Microscopic Anatomy
–
Mitochondria: produce adenosine triphosphate (ATP), a
compound that stores energy needed for muscle contraction
–
Transverse tubules: network of tubules that run at right angles
to sarcomeres & transmit nerve impulses from sarcolemma to
cell interior
–
Sarcoplasmic reticulum: network of fluid-filled chambers that
covers each myofibril like a lacy sleeve; stores calcium ions
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Physiology of Muscle Contraction
• Steps Involved in Initiating Muscle Contraction
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1. A neuron sends electrical signal (action potential) down axon
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2. Signal reaches ends of axon branches, stimulates release of
neurotransmitter acetylcholine (ACh)
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3. ACh molecules cross synaptic cleft & bind with receptors in
sarcolemma
–
4. A muscle action potential travels along sarcolemma & down
transverse tubules
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Physiology of Muscle Contraction (cont’d)
• Neuromuscular junction
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Physiology of Muscle Contraction (cont’d)
• Sliding Filament Theory
–
1. Action potential travels to sarcoplasmic reticulum & releases
calcium ions into sarcoplasm
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2. Calcium ions bind with troponin, moving aside tropomyosin
protein strands covering binding sites on actin filament
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3. Myosin heads are charged with energy from breakdown of ATP
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4. Energy binds myosin heads to active receptor sites on actin
filament, making connections called cross-bridges
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5. Ratcheting action (power stroke) occurs as myosin heads pull
sarcomere together, shortening the strand
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6. Myosin heads bind more ATP, providing energy needed to
release hold on actin strand; process creates contractions
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Physiology of Muscle Contraction (cont’d)
• Events of muscle contraction
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Physiology of Muscle Contraction (cont’d)
• Sliding filament mechanism
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Physiology of Muscle Contraction (cont’d)
• Factors Affecting Force Production
–
Motor unit recruitment
• Motor neuron: neuron responsible for initiating motion
• Motor unit: motor neuron & all fibers it controls
• Few fibers = fine movement, less power; many fibers = no
fine movement, greater power
• One muscle is typically composed of multiple motor units
• Body can control amount of force by varying number & size of
motor units recruited
• Summation: process of recruiting more & more motor units
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Physiology of Muscle Contraction (cont’d)
• Motor unit
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Physiology of Muscle Contraction (cont’d)
• Factors Affecting Force Production
–
Cross-Sectional Area
• As myofibrils become larger, muscles increase in crosssectional area & can generate more force
–
Fiber Arrangement
• Pennate fiber arrangements generate more total force than
parallel fiber arrangements
–
Muscle Length
• Shortened muscles have decreased ability to produce force
• Muscles at resting length can produce greatest force
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Physiology of Muscle Contraction (cont’d)
• Length-tension relationship
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Skeletal Muscle Fiber Types
• Slow Twitch Fibers
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Contract slowly but are resistant to fatigue
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Rely on aerobic energy production
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Used for long-duration activities (walking, jogging)
• Fast Twitch Fibers
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Contract rapidly & powerfully but fatigue quickly
–
Larger in diameter than slow twitch fibers due to having more
myofilaments
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Rely on anaerobic energy production
–
Used for short-duration activities (sprinting, lifting)
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Skeletal Muscle Fiber Types (cont’d)
• Intermediate Fibers
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Have characteristics of both slow twitch & fast twitch fibers
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May adapt to body’s demands
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“Reservists” waiting to be called up when & where need arises
• Distribution of Fiber Types
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Intermingled & genetically determined
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Those with higher concentration of slow twitch fibers have longer,
leaner muscles & predisposition to endurance activities
–
Those with higher concentration of fast twitch fibers have larger,
thicker muscles & predisposition for sprinting or body building
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Types of Muscle Contractions
• Isometric Contractions
–
Tension is generated in muscle, but muscle length & joint angle
don’t change (pushing against an immovable object)
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Used to stabilize joints
• Isotonic Contractions
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Change muscle length & create movement
–
Two types
• Concentric: muscle shortens (lifting a book off a table)
• Eccentric: muscle lengthens (slowly lowering book to table)
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Muscle Relationships
• Agonists
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Create joint movement (prime movers)
• Synergists
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Assist agonist in creating movement
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Stabilize, steer, or contribute to a particular joint movement
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Muscles that have same action or actions are considered
synergists
• Antagonists
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Perform opposite actions of agonist (i.e., flexion/extension)
–
Critical for proper posture & controlling & finishing movements
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Muscles of the Human Body
• A. Anterior view.
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Muscles of the Human Body (cont’d)
• B. Posterior view.
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Levers in the Human Body
• A. First-class levers. B. Second-class levers. C. Thirdclass levers.
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Proprioception
• Proprioception: overall awareness of body position
• Types of Proprioceptors
–
Muscle Spindles: distributed throughout skeletal muscle &
monitor changes in tissue length
–
Golgi Tendon Organs: woven into connective tissue in tendons
& monitor changes in muscle tension
–
Vestibular Apparatus: located in inner ear & provides feedback
about head position
–
Mechanoreceptors: specialized nerve endings that deform in
response to pressure & indicate position & movement of
associated structures
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Range of Motion
• Range of motion: extent of movement possible at a
joint
• Active Range of Motion
–
Client moves a given body part through its possible motions
independently
• Passive Range of Motion
–
Client rests while therapist moves joint through its possible
movements
• Resisted Range of Motion
–
Client meets resistance from practitioner in attempting to
produce movement at a joint
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