Lecture 2

• Bones and joints


  For leverage and form framework, but cannot move the body
• Muscles


  Enable movement through alternating contraction (shortening) and relaxation
• 40 to 50% of total body weight is muscle tissue
• There are 640 muscles in the human body
• Functions of muscles


  • Movement
  • Generate force
  • Heat production
  • Protect bones and internal organs
• Types of muscle tissues


  • Skeletal muscle
  • Cardiac muscle
  • Smooth muscle
• Skeletal muscle tissue


  • Location: attached to the skeleton by tendons
  • Consists of numerous bundles of fibres (fasicles)
  • Each fasicle has numerous fibrils
• Cardiac muscle tissue


  • Location: within the heart
  • Microscopic anatomy: Striated, Uninucleated, Fibres are branched cells
  • Control: Involuntary muscles, Autorhythmicity, Influenced by hormones and neurotransmitters
• Smooth muscle tissue


  • Performs sustained contractions or alternating contraction and relaxation
• Functions of muscle tissue


  • Motion (walking, holding, head movements)
  • Stabilizing body positions
  • Regulating organ volume
  • Thermogenesis
• Motor neuron


  • Consists of the cell body, the axon and the synaptic terminals at the neuromuscular junction (NMJ)
  • Function: To deliver stimulus that causes muscle to contract
• Motor unit


  Consists of the motor neuron and all the muscle it innervates
• Properties in muscle cells

  • Excitability
  • Conductivity
  • Contractility
  • Elasticity
• Chemical synaptic transmission


  1. Action potential travels along the axon

  2. Neurotransmitter molecules released at synapse

  3. Neurotransmitter molecules bind to chemical receptor molecules on opposite neuron
• Physiology of muscle contraction

  1. Action potential arrives at axon terminal

  2. Calcium channels open and Ca2+ ions flow into motor neuron's cytosol

  3. Biochemical cascade causes neurotransmitter-containing vesicles to fuse to motor neuron's cell membrane

  4. Depolarization spreads across muscle fiber into transverse tubules

  5. Calcium ions released from sarcoplasmic reticulum, initiating muscle contraction

  6. Acetylcholinesterase degrades neurotransmitter, unhydrolysed neurotransmitter diffuses away
• Muscle tone


  A state of partial contraction throughout the whole muscle, helps maintain pressure, gives firm appearance
• Isotonic contraction


  Muscle + tendon length shortens, but tension remains the same
• Isometric contraction


  Muscle + tendon length remains the same, muscle can only shorten as much as the tendon stretches
• Muscle twitch


  Response of a muscle to one stimulus (nerve firing), a single stimulus–contraction–relaxation sequence
• Treppe


  Response of a muscle to a frequency of stimulation that results in a partial relaxation between contractions
• Extensibility


  Stretching of muscles without damage to tissue