FASCIA, MUSCLES, TENDONS

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FASCIA, MUSCLES, TENDONS
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Skeletal Muscle Structure

• Origin
• Proximal attachment
• Insertion
• Distal attachment
• Tendons
• Peritendineum
• Aponeurosis

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Skeletal Muscle Hierarchy

• Myofilament
• Thick filaments
• Myosin
• Thin filaments
• Actin
• Myofibril
• Bundle of myofilaments
• Segmentally arranged into sarcomeres

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Skeletal Muscle Hierarchy

• Myofiber
• Made up of many myofibrils
• Multinucleated in skeletal muscles
• muscle cell
• Fascicle
• Bundle of myofibers
• Muscle
• Composed of several to several hundred
  fascicles

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Connective Tissues

• Endomysium
• Surrounds a myofiber
• Perimysium
• Surrounds a fascicle

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Connective Tissues

• Epimysium
• Covers entire muscle
• Blends in with deep fascia
• Connective tissue supports provide physical
  support and a pathway for nerves and vessels.

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Myofilaments

• Actin myofilaments (F-actin)
• Polymers of G-actin
• Tropomyosin
• Troponin
• Myosin filaments
• ATPase

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Sarcomeres

• Z-line (Z-actin)
• Composed of Z-actin
• Marks ends of Z-actin
• I bands
• Part of a sarcomere composed entirely of actin

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Sarcomeres

• A band
• Part of a sarcomere composed of both actin and
  myosin
• H band
• Part of a sarcomere composed entirely of myosin

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Sliding Filament Theory

• During a contraction
• I band and H band shorten
• A band remains the same length
• Sliding occurs when ATPase heads of myosin attach
  to actin via troponin and swivel.

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Myofiber

• Sarcoplasmic reticulum
• Equivalent to endoplasmic reticulum of most
  cells.
• T-tubules
• Tubular extensions of the muscle fiber
  membrane that extend down into the cytoplasm
  (saracoplasm).
• Conduct action potential from cell membrane
  surface to interior.

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Myofiber

• Cisternae
• Saccular extensions of the sarcoplasmic
  reticulum that release calcium ions in response
  to action potential.
• Calcium ions trigger sliding of myosin and
  actin filaments, resulting in a contraction.

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Myofiber Type

• The myofiber type (red or white) depends on
  innervation.
• All myofibers in a motor unit are of the same
  type.

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Dark (red) Fibers

• Fatigue resistant
• Contract slowly (slow twitch)
• Rely on oxidative phosphorylation
• Have a large number of mitochondria
• Have a high concentration of myoglobin
• Have a low concentration of ATPase

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Light (white) Fibers

• Fatigue easily
• Contract rapidly (fast twitch)
• Rely on glycolysis
• Have a small number of mitochondria
• Have a low concentration of myoglobin
• Have a high concentration of ATPase

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Neuromuscular Junctions

• Components
• Presynaptic membrane
• Terminal end of motor neuron.
• Synaptic cleft
• Postsynaptic membrane
• Sarcolemma (cell membrane of myofiber)

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Motor Unit

• Consists of a motor neuron and all the myofibers
  it innervates
• Units for fine control have fewer fibers
• Units for gross control have many fibers

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Muscle Classification

• Fiber arrangement
• Shape
• Origin and insertion
• Function

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Fiber Arrangement

• Straight
• Example rectus abdominis
• Fusiform
• Example biceps brachii
• Unipennate
• Example palmar interosseous muscles
• Bipennate
• Example dorsal interosseous muscles
• Multipennate
• Example deltoid muscle

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Muscle Shape

• Deltoid
• Trapezius

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Muscle Origin/Insertion

• Coracobrachialis
• Sternocleidomastoid

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Muscle Function

• Pronater teres
• Extensor digitorum

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Contraction

• Definition
• A contraction is a muscles response to a
  stimulus.
• Types of contraction
• Isotonic (the length of the muscle changes)
• Concentric (length decreases)
• Eccentric (length increases)
• Isometric (the length of the muscle stays the
  same)

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Types of Action

• Agonist (prime mover)
• A muscle that primarily carries out the
  desired action.
• Antagonist
• A muscle that opposes the agonist.
• Synergist
• A muscle that eliminates the unwanted action
  of the agonist.

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Types of Action

• Fixator
• A muscle that stabilizes the origin of another
  muscle.
• Note a single muscle can be all the above at one
  time or another.

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Insufficiency

• Refers to the inability of a multijoint muscle to
  maximally contract simultaneously over all joints
  crossed.
• Active
• Refers to the agonist
• Passive
• Refers to the antagonist

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Smooth Muscle

• Synonyms
• Visceral
• Involuntary
• Found in
• Walls of visceral tubes (intestines, etc.)
• Associated with hair follicles
• Around glandular structures
• In walls of blood vessels

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Smooth Muscle Characteristics

• Bundles of sheets of individual cells.
• Not striated (smooth).
• Cells are primarily elongated and tapered.
• Mononucleated.

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Smooth Muscle Characteristics

• Nuclei are centrally located in each cell.
• Does not conduct action potential.
• Cells connected by gap junctions.
• Not under voluntary control.

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Cardiac Muscle Tissue

• Found only in walls of heart.
• Characteristics
• Striated (sarcomeres)
• Mononucleated cells
• May branch
• Intercalated discs
• Sites of transfer of stimulus between adjacent
  cells.

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