Muscular System

  • There are three types of muscles, all animals have some form of muscle most of which are smooth and striated

    • Striated (skeletal): Composed of fascicles of several muscle fibers.
    • Each fiber is made up of bundles of myofibrils of actin and myosin myofilaments.
    • The actin and myosin of the myofilaments are arranged into contractile units called sarcomeres which is what makes it look striated
    • Cells have multiple nuclei
    • Smooth
    • Cardiac: Found only in the hearts of vertebrates
    • Striated with branched cells, adjacent cells are connected with intercalated discs that contain gap junctions which enable the heart to function as a unit
    • Cells have one nuclei
    • Involuntary action that is partially controlled within the heart
    • Cells do not fatigue

  • Neuromuscular Junction: Where somatic nerves synapses with muscle fibres

  • Acetylcholline leaves nerves and binds to receptors in muscles. This opens sodium ion channels which spread into the cell. T-tubules release calcium ion which binds to troponin exposing myosin binding sites on actin and allows muscles to contract

  • Motor Unit: A group of fibres controlled by one nerve. More precise movements requires more motor units, less precise movements requires more fibres per neuron.

  • Muscles are antagonistic

  • Origin: attachement to bone that is stationary

  • Insertion: attachement to bone that moves

  • Isotonic: muscle tension doesn’t change, size does, ex. lifting weights

  • Isometric: Muscle tension changes, muscle size does not, ex. holding an object at your side

  • Striated muscle evolved to enable complex movements requiring greater nervous system control. It can generate faster movements and more force than smooth muscles

  • Striated and skeletal muscles are used in locomotion and posture, their action is voluntary and contraction can be fast or slow

  • Arthropods only have striated muscles

  • Skeletal muscles can be stimulated to contract by electrical impulses

  • Twitch: A quick contraction and then relaxes

  • When a second impulse is delivered immediately after the first and creates a summation

  • Increasing frequency of impulses decreases the relaxion period between twitches and increases the strength of a contraction

  • Tetanus: A smooth sustained contraction which is achieved after a particular frequency of stimuli

  • Slow-twitch: Lots of capillaries, many mitochondria, numerous respiratory enzymes, lots of myoglobin

  • Red fibers: More myoglobin, operates aerobically and can sustain activity for a long time without fatigue

  • Fast-twitch: Fewer capillaries and mitochondria, less myoglobin

  • White fibres: Less myoglobin, can operate anaerobically and are adapted for rapid generation of power, lack endurance

  • A band (dark): is overlapping thick (myosin) and thin (actin) filaments.

  • H band: shortens as myosin and actin move along one another also the thick filaments only.

  • Z line: is the end of each sarcomere.

  • I band (light): is thin (actin) filaments only