HPP

• Skeletal muscle


  Attached to bones, striated, voluntarily controlled
• Cardiac muscle


  Located in the heart, striated, involuntarily controlled
• Smooth muscle


  Located in blood vessels and hollow organs, non-striated, involuntarily controlled
• Functions of the muscular system

  • Movement
  • Maintain posture
  • Respiration
  • Production of body heat
  • Communication
  • Heart beat
  • Contraction of organs and vessels
• Properties of muscles


  • Contractility - ability to shorten forcefully
  • Excitability - capacity to respond to a stimulus
  • Extensibility - ability to be stretched beyond normal resting length and still contract
  • Elasticity - ability to recoil to original resting length after being stretched
• Skeletal muscle


  • Constitutes approximately 40% of body weight
  • Many muscles attached to skeletal system
  • Some attached to skin or connective tissue sheets
  • Transverse bands/striations visible under microscope
  • Comprised of muscle, nerve, and connective tissue

  
• Connective tissue coverings of skeletal muscle

  • Epimysium - surrounds entire muscle
  • Perimysium - surrounds fascicles
  • Endomysium - surrounds individual muscle fibers

  
• Muscle fiber structure


  • Single cylindrical cell with multiple nuclei at periphery
  • Length 1-30 cm, diameter 0.15 mm
  • Sarcolemma has T-tubules that connect to sarcoplasmic reticulum
  • Sarcoplasmic reticulum has high Ca2+ concentration for contraction
  • Cytoplasm (sarcoplasm) contains myofibrils with actin and myosin filaments
• Motor neuron


  Nerve cell that stimulates muscle cells
• Neuromuscular junction


  Synapse where nerve fiber connects with muscle fiber
• Motor unit


  Group of muscle fibers stimulated by a single motor neuron
• Presynaptic terminal


  End of neuron axon fiber
• Synaptic cleft


  Space between presynaptic terminal and postsynaptic membrane
• Postsynaptic membrane


  Muscle fiber membrane (sarcolemma)
• Synaptic vesicle


  Vesicle in presynaptic terminal that stores and releases neurotransmitters
• Neurotransmitter


  Chemical that stimulates or inhibits postsynaptic cells
• Acetylcholine


  Neurotransmitter that stimulates skeletal muscles
• Muscle fibers are very energy-demanding cells
• Sources of energy for muscle contractions

  • Aerobic ATP production
  • Anaerobic ATP production
  • Conversion of creatine phosphate to ATP
  • Conversion of ADP to ATP and AMP
• Mechanisms of muscle fatigue

  • Acidosis and ATP depletion
  • Oxidative stress (buildup of reactive oxygen species)
  • Local inflammatory reactions
• Isometric contraction


  Increase in muscle tension with no change in length
• Isotonic contraction


  Change in muscle length with no change in tension
• Concentric contraction


  Isotonic contraction where muscle shortens as tension increases
• Eccentric contraction


  Isotonic contraction where muscle lengthens while maintaining tension
• Muscle tone


  Constant tension produced by muscles over long periods to maintain posture
• Smooth muscle


  • Non-striated, small spindle-shaped cells with one nucleus
  • Myofilaments not organized into sarcomeres
  • Comprise organs controlled involuntarily (except heart)
  • Stimulated by neurotransmitters, hormones, and other substances
• Cardiac muscle


  • Long, striated, branching cells with one nucleus per cell
  • Contraction is autorhythmic
• Muscle tone


  • Depends on a small percentage of all the motor units in a muscle being stimulated at any point in time, causing their muscle fibers to contract tetanically and out of phase with one another
• Smooth muscle cells


  Non-striated small, spindle-shaped muscle cells, usually with one nucleus per cell
• Smooth muscle


  • The myofilaments are not organized into sarcomeres
  • The cells comprise organs controlled involuntarily, except the heart
  • Neurotransmitter substances, hormones, and other substances can stimulate smooth muscle
• Cardiac muscle cells


  Long, striated, and branching, with usually only one nucleus per cell
• Cardiac muscle


  • Striated as a result of the sarcomere arrangement
  • Contraction is autorhythmic
  • Cells are connected to one another by specialized structures that include desmosomes and gap junctions called intercalated disks
  • Function as a single unit in that action potential in one cardiac muscle cell can stimulate action potentials in adjacent cells
• Tendon


  Connects skeletal muscle to bone
• Aponeuroses


  Broad, sheetlike tendons
• Retinaculum


  A band of connective tissue that holds down the tendons at each wrist and ankle
• Skeletal muscle attachments


  Have an origin and an insertion, with the origin being the attachment at the least mobile location and the insertion being the end of the muscle attached to the bone undergoing the greatest movement
• Belly


  The part of the muscle between the origin and the insertion
• Agonists


  A group of muscles working together
• Antagonists


  A muscle or group of muscles that oppose muscle actions
• Muscles are named according to

  • Location
  • Size
  • Shape
  • Orientation of fascicles
  • Origin and insertion
  • Number of heads
  • Function