muscular system

• Muscle Tissue


  Represents ~50% body mass in adult humans, can be divided into 3 types: skeletal, cardiac, smooth
• Muscle Types


  • Skeletal
  • Cardiac
  • Smooth
• Skeletal Muscle


  • Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement
  • Voluntary
• Smooth Muscle


  • Walls of hollow organs, blood vessels, eye, glands, skin
  • Some functions: propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow
  • In some locations, autorhythmic
  • Controlled involuntarily by endocrine and autonomic nervous systems
• Cardiac Muscle


  • Heart: major source of movement of blood
  • Autorhythmic
  • Controlled involuntarily by endocrine and autonomic nervous systems
• Muscle Naming Conventions


  • Location
  • Size
  • Shape
  • Orientation of fascicles
  • Origin and insertion
  • Number of heads
  • Function
• Functions of the Muscular System

  • Body posture
  • Support and protection
  • Sphincter control
  • Movement of food along GIT
  • Regulation of blood flow
  • Temperature regulation
• Characteristics of All Muscles

  • Excitability - responsive to stimuli
  • Contractility - ability to shorten forcibly when adequately stimulated
  • Extensibility - can extend beyond their resting/relaxed length
  • Elasticity - recoil and resume its resting length after stretching
• Muscle Cell Terminology

  • Muscle cell = myocyte or myofibre
  • Muscle cell cytoplasm = sarcoplasm
  • Muscle cell membrane/plasmalemma = sarcolemma
  • Endoplasmic reticulum = sarcoplasmic reticulum (SR)
• Muscle Cell Components


  • Cell membrane - sarcolemma
  • Cytoplasm - sarcoplasm
  • Nuclei, organelles
  • Full of myofibrils - actin/myosin
  • Many mitochondria
  • Extensive endoplasmic reticulum - sarcoplasmic reticulum
• Common Features of All Muscles

  • Actin and myosin - generate force for contraction
  • Calcium ions - needed for activation of contraction
  • Supply of ATP - generated via respiration: aerobic oxidative respiration, anaerobic glycolytic respiration
  • Stimulation - need an action potential from a neurone
• Actin

  • Actin subunits ("G actin") polymerise into long, filamentous or "F actin"
  • Two intertwined actin filaments
  • Active sites to which myosin head attaches in contraction
  • Regulatory proteins: Tropomyosin stabilises actin, Troponin binds actin, tropomyosin and calcium
• Myosin

  • Rod-like tail attached by flexible hinge to two globular heads
  • Tail - two intertwined helices
  • Globular heads link thick and thin filaments in contraction
  • Cross bridges - motors (force)
  • Actin and ATP-binding sites
  • Intrinsic ATPase activity
• Actin and Myosin Interaction
• Muscle Cell Design for Function

  • Smooth muscle cells
  • Cardiac muscle cells
  • Skeletal muscle cells
• Smooth Muscle Cells


  • Small - 100-200 µm in length
  • Spindle shaped cells arranged into sheets
  • Less regularly organised
  • No striations
  • Single nucleus
• Smooth Muscle


  • Sheets of smooth muscle cells arranged in sheets perpendicular to each other
  • Blood vessels: regulates lumen diameter - contributes to maintenance of blood pressure
• Smooth Muscle Contraction


  • Smooth muscle is stimulated by the ANS, hormones and in response to stretch
  • Slower contraction rate - longer duration than cardiac or skeletal muscle
• Cardiac Muscle - Gross Anatomy

  • Continually contracts at a steady rate
  • Can contract without stimulation - myogenic
  • Involuntary muscle - autonomic nervous system (ANS)
  • Branched cells
  • Small - 100 µm in length
  • Uni- or bi-nucleated
  • Striated
  • Intercalated disks
  • Aerobic oxidative metabolism
• Skeletal Muscle


  • >40% Body Mass
  • ~640 muscles
  • Body movement
  • Attached to the skeleton via tendons
  • Large cells
  • Voluntary control
  • Sporadic and continual contraction
• Fascicle


  Bundle of muscle fibres
• Muscle Movements


  Muscles and their tendons and bones act together as lever systems to move either parts of the body or the whole body
• Lever Classes


  • Class I - Fulcrum between force and weight
  • Class II - Weight is between fulcrum and pull
  • Class III - Pull located between fulcrum and weight
• Myofibre/Myocyte


  Muscle cell containing myofilaments
• Myofilament


  Contractile units called SARCOMERES
• Sarcomere


  • Basic functional unit of muscle fiber; smallest part that can contract
  • Z disk: filamentous network of protein, serves as attachment for actin myofilaments
  • I bands: lighter-staining regions, each containing a Z disk and extend to ends of myosin myofilaments
  • A bands: central dark-staining region; overlapping actin and myosin myofilaments (except at center)
  • H zone: region in A band where actin and myosin do not overlap
  • M line: middle of H zone; delicate filaments holding myosin in place
  • Titin filaments: elastic chains of amino acids; make muscles extensible and elastic
• Sliding Filament Theory


  Mechanism of skeletal muscle contraction