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Chapter 10: Skeletal Muscle Tissue - Coggle Diagram

- - - - Muscle Tone
        Constant, low-level contraction of muscles
  - - - Sheaths of Skeletal Muscle Fibers
        
        Several sheaths of connective tissue hold the fibers of a skeletal muscle together
        
        From external to internal:
        
        Epimysium
        
        Perimysium
        
        Endomysium
        
        Continuous with each other
        
        Form tendons together
        
        Provide a muscle with natural elasticity
        
        Carry then blood vessels & nerves that serve the muscle fibers
        
        Epimysium
        
        Outer layer of dense irregular connective tissue
        
        Surrounds the whole skeletal muscle
        
        Perimysium
        
        Fibrous/dense connective tissue
        
        Surrounds each fascicle
        
        Muscle fibers within each skeletal muscle are separated into groups (fascicles)
        
        Endomysium
        
        Loose connective tissue
        
        Surrounds each muscle fiber within a fascicle
        
        Tendons
        
        All 3 sheaths converge to form the tendon
        
        Tendon: connective tissue structure that joins skeletal muscles to bones
        
        Nerves & Blood Vessels
        
        Each skeletal muscle is supplied by 1 nerve, 1 artery & 1 or more veins
        
        Nerves & vessels branch repeatedly in the intramuscular connective tissue
        
        Smallest branches serve individual muscle fibers
        
        Rich blood supply to muscles reflects high demand for nutrients & oxygen by contracting muscle fibers
        
        Motor Neurons
        
        Nerve cells that innervate muscle fibers
        
        The axon of a motor neuron branches to inner several fibers in a skeletal muscle
        
        Motor Unit
        
        Composed of a motor neuron & all the muscle fibers it innervates
        
        When motor neuron fires, all the skeletal muscle fibers in the motor unit contract together
        
        Muscles that require very fine control have few muscle fibers per motor unit
        
        Bulky, weight-bearing muscles that require less precise control have more muscle fibers per motor unit
        
        Size & number of motor units depends on the muscle
        
        Recruitment
        
        Addition of motor units to accomplish a movement
        
        For a small force, a small # of motor units are stimulated
        
        For a bigger force, additional motor units are recruited
        
        Neuromuscular Junction
        
        Each muscle fiber in a skeletal muscle is served by a nerve ending
        
        Signals the fiber to contract
        
        Point where the nerve ending & fiber meet is called the neuromuscular junction
        
        Terminal Boutons/Axon Terminals
        
        Cluster of enlargements at the end of the axon that stores neurotransmitters
        
        Contains vesicles that relate neurotransmitter when a nerve impulse reaches the terminals
        
        Neurotransmitter at the neuromuscular junction is acetylcholine
        
        Neurotransmitter diffuses across synaptic cleft & binds to receptor molecules on sarcolemma
        
        Separated from the sarcolemma of the muscle fiber via the synaptic cleft
      - Muscle Attachments
        
        Location on a bone where a muscle connects to the bone
        
        Extends from 1 bone to another
        
        Crosses at least 1 moveable joint
        
        When the muscle contracts, it causes 1 of the bones to move while the other bone is fixed
        
        Origin
        
        Attachment on the less movable bone is the origin
        
        Insertion
        
        Attachment on the more movable bone is the insertion
        
        When muscle contracts, its insertion is pulled toward the origin
        
        Usually, in the limbs, the origin is the more proximal attachment of the muscle & the insertion is the more distal attachment
        
        Attach via strong fibrous connective tissues that extend into the fibrous periosteum of the bone
        
        Many muscles span 2 or more joints
        
        Biarticular/multijoint muscles
        
        Types of Muscle Attachments
        
        Direct/Fleshy Attachments
        
        The attaching strands of connective tissue are super short; intercostals
        
        Muscle fascicles appear to be directly attached to the bone
        
        Indirect Attachments
        
        The connective tissue extends well beyond the end of the muscle fibers
        
        Forms a cordlike tendon or a flat sheet called an aponeurosis; biceps
        
        More common than direct attachments
        
        Most muscles have tendons
        
        Raised bone markings (tubercles, trochanters & crests) are often present where tendons meet bones
        
        Most tendons & aponeuroses attach to bones
        
        Some attach to skin, cartilage, sheets of fascia or raphe
      - Striations
        
        Result from the internal structure of long, rod-shaped organelles called myofibrils
        
        Myofibrils
        
        Unbranched cylinders that make up 80+% of sarcoplasm
        
        Specialized contractile organelles unique to muscle tissue
        
        Contain myofilaments, mitochondria & glycosomes
        
        Composed of repeating segments called sarcomeres
        
        Sarcomeres
        
        Basic unit of contraction in skeletal muscle
        
        Boundaries at the 2 ends of each sarcomere are called Z discs/lines
        
        Myofilaments
        
        Actin Filaments
        
        Attached to each Z disc & extending toward the center of the sarcomere
        
        Fine/thin filaments
        
        Composed primarily of the contractile protein actin
        
        Troponin & tropomyosin (2 regulatory proteins) are found on the thin filament
        
        Control the interaction of actin with the thick filaments
        
        Troponin
        
        Globular protein with 3 binding sites, 1 for actin, tropomyosin, and for calcium
        
        Attaches the tropomyosin strand to the actin molecule
        
        Tropomyosin
        
        Forms a thin strand that spirals around the actin molecule
        
        Myosin Filaments
        
        In the center of the sarcomere & overlapping the inner ends of the thin filaments
        
        Cylindrical bundle
        
        Thick filaments
        
        Consist largely of myosin molecules
        
        Contain ATPase enzymes that break apart ATP to release energy needed for muscle contraction
        
        Both ends of a thick filament are studded with globular myosin heads
        
        Titin
        
        Springlike molecule in sarcomeres that resists overstretching
        
        Found in the elastic filaments of the sarcomere
        
        Extend from Z disc to the thick filament & run within the thick filament to attach to the M line
        
        2 basic functions:
        
        Holds the thick filaments in place in the sarcomere
        
        Contributes to muscle elasticity
        
        Contraction
        Cross bridge cycling/Sliding filament theory
        
        Ca2+ binds to troponin on actin
        
        Troponin pulls tropomyosin away from myosin binding sites
        
        Allows cross bridge between myosin & actin
        
        Power stroke causes myosin head to swivel & pull actin towards the center
        
        ADP & Pi released
        
        ATP binds to myosin head, causing it to release actin
        
        ATPase on myosin filament produces ADP + Pi
        
        Energy released rechecks myosin head
        
        Relaxation
        1) Termination of the nerve signal
        
        Terminates the release of Ach (Acetylcholine) by acetylcholinesterase
        2) Na+ gates close in sarcolemma
        3) Ca2+ channels close in SR
        4) Ca2+ pumped back into SR with ATP
        5) Troponin releases tropomyosin back into blocking position
        6) Muscle cell relaxes
        
        Sarcoplasmic Reticulum
        
        Elaborate, smooth endoplasmic reticulum
        
        Mostly runs longitudinally & surrounds each myofibril
        
        Regulates intracellular calcium levels
        
        Storage for Ca2+
        
        Types of Muscle Contractions
        
        Isotonic Contractions
        
        Myofilaments are able to slide past each other during contractions
        
        The muscle shortens & movement occurs
        
        Ex: bending the knee, lifting weights, smiling
        
        Isometric Contractions
        
        Muscle filaments are trying to slide, but the muscle is pitted against an immovable object
        
        Tension increases, but muscles don't shorten
        
        Ex: pushing your palms together in front of you
      - Muscle Classification
        
        Functional Groups
        
        Prime Movers
        Provide the major force for producing a specific movement
        
        Antagonists
        Oppose/reverse a particular movement
        
        Synergists
        
        Work cooperatively to achieve a certain action
        
        Add force to a movement
        
        Reduce undesirable/unnecessary movement
        
        Fixators
        
        Synergists that immobilize a bone/muscle's origin
        
        Naming of Skeletal Muscles
        
        Location of Muscle
        Bone/body region associated with the muscle
        
        Shape of Muscle
        Ex: deltoid = triangle
        
        Relative Size
        
        Maximus: largest
        
        Minimus: smallest
        
        Longus: long
        
        Bervis: short
        
        Direction of Fibers
        
        Rectus: fibers run straight
        
        Tranversus
        
        Oblique: fibers run at angles to an imaginary defined axis
        
        Number of origins
        
        Ex: Biceps (2 origins), triceps (3 origins)
        
        Location of Attachments
        
        Named according to point of origin or insertion
        
        Action
        
        Flexor or extensor
        
        Muscles that flex or extend
    - - Visceral Muscle
        
        Cardiac & smooth muscle tissue are called visceral muscle
        
        Both occur in the visceral organs
        
        Both are innervated by involuntary division of nervous system