MUSCLE TISSUE

Cards (48)

  • Muscle tissue

    Differentiated cells that possess contractile filaments, classified according to morphology and function, contraction may be voluntary or involuntary
  • General functional characteristics of muscle

    • Posture maintenance
    • Movement
    • Joint stabilization
    • Heat generation
  • Special functional characteristics of muscle

    • Contractility (shorten and generate pulling force)
    • Excitability (respond to stimuli)
    • Extensibility (stretch with contraction of opposing muscle)
    • Elasticity (recoil passively after stretch)
  • Isotonic
    Type of muscle contraction. Muscle Tension using the same weight.
  • Isometric
    Type of muscle contraction. Muscle Tension developed without changing the
  • Types of muscle tissue

    • Skeletal
    • Cardiac
    • Smooth
  • Skeletal muscle

    • Attach to and move skeleton, 40% of body weight, fibers are multinucleated, visible striations, voluntary
  • Cardiac muscle

    • Found only in heart wall, myocardium, striated, involuntary
  • Smooth muscle

    • Found in hollow visceral organs, no visible striations, involuntary
  • Skeletal muscle structure

    1. Myofibril
    2. Muscle fiber
    3. Muscle fascicle
    4. Skeletal muscle (organ)
  • Skeletal muscle general concepts and structure
    • Multinucleated, cytoplasm is sarcoplasm, plasma membrane is sarcolemma. Sarcolemma forms deep tubular invaginations (T-tubules), consists largely of myofibrils, sarcoplasmic reticulum is a modified smooth ER, T-tubules and sarcoplasmic reticulum form a triad
  • Skeletal muscle myofibrils

    • Composed of contractile proteins (myofibrils), myofibrils are divided into segments called sarcomeres (contractile/functional units), composed of alternating thick (myosin) and thin (F-Actin) filaments (collectively known as myofilaments), Z line/disc marks sarcomere boundary
  • Skeletal muscle proteins

    • Contractile proteins (e.g. Actin and Myosin - generate force during contraction)
    • Regulatory proteins (e.g. Troponin and Tropomyosin - switch the contraction process on and off)
    • Structural proteins (e.g. Titin and Dystrophin - align the thick and thin filaments properly, provide elasticity and extensibility, link the myofibrils to the sarcolemma)
  • Skeletal muscle contraction

    1. Action potential at NMJ transmitted along T-tubules to terminal cisterna of SR, release of calcium
    2. Ca++ binds to troponin, myosin heads bind to actin, creating cross bridges
    3. Cross bridges pull on thin filaments, sarcomere shortens
    4. Ca++ goes back into sarcoplasmic reticulum, contraction stops
  • Skeletal muscle microscopic appearance

    • Cells are elongated, do not branch, larger diameter, nucleus is multinucleated, flattened and peripherally located, myoblasts are embryonic cells that fuse to develop muscle fibers
  • Skeletal muscle fiber microscopic appearance

    • Myofibrils are striated with distinct myofilaments (actin & myosin), alternating light and dark bands, dark bands (A bands) are anisotropic/birefringent, light bands (I bands) are isotropic/do not alter polarized light
  • Skeletal muscle distribution

    • Widely distributed, attached to entire skeletal system of the body, external urethral & external anal sphincter, tongue (although unattached to skeletal system), upper 1/3 of the esophagus (lower part is involuntary smooth muscle)
  • Types of skeletal muscle

    • Red/Slow (Type I)
    • Red/Fast (Type IIa)
    • White/Fast (Type IIb)
  • Cardiac muscle

    • Bundles form thick myocardium, cardiac muscle cells are single cells (not called fibers), auto rhythmicity (each cell beats separately even without stimulation), involuntary activation (like smooth muscle), very fatigue resistant
  • Cardiac muscle microscopic appearance

    • Spherical centrally located nucleus (branches have no nucleus), with intercalated discs of Eberth (serve as junction between cardiac cells), elongated branches with numerous areolar CT, myofibrils striated with distinct actin & myosin
  • Cardiac muscle ultrastructure

    • T-tubules are larger, located at Z-disk, sarcoplasmic reticulum is poorly defined, contributes to dyads, dyads consist of one T-tubule and one terminal cisterna of SR
  • Muscle types

    • Skeletal
    • Cardiac
    • Smooth
  • Skeletal muscle

    • Long cylindrical shape
    • Multiple peripheral nuclei
    • Striated
    • Triad at A-I junction
    • Voluntary contraction
  • Cardiac muscle

    • Branched shape
    • Single central nucleus
    • Striated
    • Dyad at Z disc
    • Involuntary contraction
  • Smooth muscle

    • Short spindle shape
    • Single central nucleus
    • No striations
    • Caveola and some ER
    • Gap junctions
    • No sarcomeres
    • Involuntary contraction
  • Smooth muscle contraction is initiated by the calcium-activated phosphorylation of myosin rather than calcium binding to troponin
  • Smooth muscle contraction

    1. Intracellular calcium binds with calmodulin
    2. Calmodulin-myosin light-chain kinase complex phosphorylates myosin
    3. Activates myosin ATPase
  • Smooth muscle contraction involves the interaction of sliding actin and myosin filaments, similar to skeletal muscle
  • Smooth muscle is very fatigue resistant
  • Smooth muscle contraction is slow and sustained
  • Smooth muscle is involuntary and cannot be consciously controlled
  • Functions of smooth muscle

    • Alter activity of various body parts to meet their specific needs
    • Contraction of urinary bladder
    • Move food through intestines (peristalsis)
    • Peristaltic movement to move feces down digestive system
    • Contraction in trachea and bronchi to decrease airway size
    • Constriction and dilation of blood vessels to regulate blood pressure
    • Constriction, accommodation and dilation of pupil
    • Uterine contraction during birthing
    • Expulsion of glandular contents
    • Arrector pili muscle causes "goosebumps" for thermoregulation
  • Smooth muscle is distributed in the eye, respiratory tubes, urinary organs, reproductive organs, digestive tubes, walls of blood vessels, and skin
  • Cardiac muscle is responsible for generating and conducting electrical impulses for the heart, causing the heart to contract and pump blood throughout the body
  • Components of the cardiac conduction system

    • Sinoatrial (SA) node
    • Atrioventricular (AV) node
    • Bundle of His
    • Left and right bundle branches
    • Purkinje fibers
  • Sinoatrial (SA) node

    Regulates heart rate and rhythm
  • Atrioventricular (AV) node

    Delays cardiac impulses from SA node to allow atria to contract and empty first, then relays impulses to the atrioventricular bundle
  • Atrioventricular bundle of His

    Carries cardiac impulses down the septum to the ventricles via the Purkinje fibers
  • Left and right bundle branches
    Carry nerve impulses that cause contraction of the left and right ventricles respectively
  • Purkinje fibers

    Modified cardiac muscle cells specialized for conduction, trigger waves of contraction through both ventricles simultaneously