Muscular System

• Muscular System


  Muscles are responsible for all types of body movement
• Basic muscle types


  • Skeletal muscle
  • Cardiac muscle
  • Smooth muscle
• Physiological properties of muscles

  • Irritability or Excitability - to be stimulated
  • Contractility - to contract (shorten)
  • Extensibility - to be stretched
  • Elasticity - return to original position after being stretched
• Functions of muscles


  • Produce movement
  • Maintain posture
  • Stabilize joints
  • Generate heat
• Mobility


  • Gross movement - large, coordinated motions (walking, running, swimming)
  • Fine movement - smaller movements (writing, speaking, facial expressions)
• Stability

  • Muscle tendons stretch over joints and contribute to joint stability
  • Core muscles stabilize the body and assist in tasks
• Posture


  • Skeletal muscles help keep the body in the correct position
  • Good posture relies on strong, flexible muscles
  • Bad posture leads to joint and muscle pain
• Temperature regulation


  • Almost 85 percent of the heat a person generates comes from contracting muscles
  • Skeletal muscles increase activity to make heat when body heat falls below optimal levels
  • Smooth muscle in blood vessels contracts to maintain body heat
• Origin


  Heads of a muscle
• Insertion


  Slips of a muscle
• Skeletal muscle attachments


  • Epimysium - fibrous connective tissue layer
  • Perimysium - fibrous sheath enveloping fascicles
  • Endomysium - fine connective tissue sheath surrounding a muscle fiber
• Muscle structure


  • Muscle fibers composed of myofibrils
  • Myofibrils composed of thick filaments (myosin) and thin filaments (actin)
  • Filaments arranged in sarcomeres separated by Z discs
• Thick filaments


  Myosin filaments with ATPase enzymes
• Thin filaments


  Actin filaments
• Myosin and actin filaments overlap somewhat
• Sliding-filament theory


  Muscle contracts when thin filaments slide over thick filaments
• All-or-None Law - A muscle either contracts fully or not at all
• Motor unit


  One neuron and the muscle cells it stimulates
• Muscle contraction: Excitation-Contraction Coupling

  1. Liminal/Minimal stimulus

  2. Subliminal/Sub-minimal stimulus

  3. Threshold of stimulation
• Roles of muscles


  • Agonist - prime mover
  • Antagonist - action opposite to agonist
  • Stabilizers - fixate or stabilize the joint
  • Synergists - assist or guide
• Muscle twitch


  Single muscle contraction that lasts for a fraction of a second
• Tetanus


  Sustained contraction from rapid stimulation with no relaxation
• Summation


  Increasing the force of contraction of muscle fibers within the muscle
• Rigor mortis


  Body stiffness after death due to coagulation of protein
• Energy sources for muscle contraction

  • ATP - direct phosphorylation
  • Creatine phosphate - regenerates ATP
  • Aerobic respiration - glucose breakdown with oxygen
  • Anaerobic glycolysis - glucose breakdown without oxygen
• Muscle fatigue


  Inability to contract due to oxygen debt, lactic acid buildup, and lack of ATP
• Types of ordinary body movements

  • Flexion
  • Adduction
  • Extension
  • Rotation
  • Abduction
  • Circumduction
  • Dilation
  • Constriction
  • Supination
  • Pronation
• Factors used in naming skeletal muscles

  • Direction of muscle fibers
  • Relative size of the muscle
  • Location of the muscle
  • Number of origins
  • Location of origin and insertion
  • Shape of the muscle
  • Action of the muscle
• Muscle groups


  • Muscles of the head and neck
  • Trunk muscles
  • Muscles of the lower leg
• Muscular System

  Muscles are responsible for all types of body movement
• Basic muscle types

  • Skeletal muscle
  • Cardiac muscle
  • Smooth muscle
• Physiological properties of muscles

  • Irritability or Excitability - to be stimulated
  • Contractility - to contract (shorten)
  • Extensibility - to be stretched
  • Elasticity - return to original position after being stretched
• Functions of muscles

  • Produce movement
  • Maintain posture
  • Stabilize joints
  • Generate heat
• Mobility

  • Gross movement - large, coordinated motions (walking, running, swimming)
  • Fine movement - smaller movements (writing, speaking, facial expressions)
• Stability

  • Muscle tendons stretch over joints and contribute to joint stability
  • Core muscles stabilize the body and assist in tasks
• Posture

  • Skeletal muscles help keep the body in the correct position
  • Good posture relies on strong, flexible muscles
  • Bad posture leads to joint and muscle pain
• Temperature regulation

  • Almost 85 percent of the heat a person generates comes from contracting muscles
  • Skeletal muscles increase activity to make heat when body heat falls below optimal levels
  • Smooth muscle in blood vessels contracts/relaxes to maintain body temperature
• Origin

  Heads of a muscle
• Insertion

  Slips of a muscle
• Skeletal muscle attachments

  • Epimysium - fibrous connective tissue layer
  • Perimysium - fibrous sheath enveloping fascicles
  • Endomysium - fine connective tissue sheath surrounding a muscle fiber