FASCIA, MUSCLES, TENDONS

Skeletal Muscle Structure Origin: Proximal attachment Insertion: Distal attachment Tendons: Peritendineum Aponeurosis

Skeletal Muscle Hierarchy Myofilament: Thick filaments Myosin Thin filaments Actin Myofibril: Bundle of myofilaments Segmentally arranged into sarcomeres

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

Connective Tissues Endomysium: Perimysium: Surrounds a myofiber Surrounds a fascicle

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

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

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

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

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.

Myofiber Sarcoplasmic reticulum: T-tubules: 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.

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.

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

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

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

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

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

Muscle Classification Fiber arrangement Shape Origin and insertion Function

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

Muscle Shape Deltoid Trapezius

Muscle Origin/Insertion Coracobrachialis Sternocleidomastoid

Muscle Function Pronater teres Extensor digitorum

Contraction Definition: Types of contraction: A contraction is a muscle’s 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)

Types of Action Agonist (prime mover): Antagonist: Synergist: 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.

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.

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

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

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

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

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.