Chapter 11 Muscular System

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					Human Biology- Bio 107
Chapter 6: The Muscular System

I. Types and Functions of Muscles

  A. Types of muscle

    1. Skeletal muscle- tubular, multinucleated, striated, voluntary
    2. Smoothmuscle- fusiform, uninucleated, non-striated, involuntary
    3. Cardiac muscle- striated, branched, uninucleated, involuntary

  B. Functions of Skeletal Muscles:

    1. support
    2. movement
    3. body temperature
    4. aid movement in blood and lymph vessels
    5. protect internal organs, stabilize joints

  C. All muscles have three fundamental features:
    1. excitability (contract in response to chemical/electrical signals)
    2. contractibility (shorten)
    3. relaxation (lengthen)

  D. ~600 Skeletal Muscles in the Body-        Fig 6.2
       contraction causes movement

    1. basic structure     Fig 6.3, 6.4, 6.5

       a. muscles made up of bundles of muscle fibers (fascicles)
          (a muscle fiber is a muscle cell)
       b. covered with CT (fascia)
          1. tendons- CT that extends beyond muscle to connect it to bones
       c. fascicle is made up of muscle fibers (cells)
       d. origin- on stationary bone
       e. insertion- on the bone that gets moved

    2. Muscles Work in Pairs       Fig 6.1

       a. prime mover- does most of work
      b. synergists- groups of muscles that work together
      c. antagonists- groups of muscles that work in opposition to on another
         biceps: triceps
      d. when muscles shorten, bones are moved
      e. When a muscle contracts (shortens) the insertion is pulled toward
         the origin.

    3. Naming Muscles- based on several characteristics

      a. size
      b. shape
      c. location
      d. direction of fibers
      e. attachment
      f. number of attachments
      g. action

II. Mechanism of Skeletal Muscular Muscle Fiber Contraction

  A. Muscle Cell structure     Fig 6.5, 6.6, 6.7, 6.8

    1. muscle fiber (muscle cell)
    2. sarcoplasm- cytoplasm
    3. sarcolemma- plasma membrane
    4. sacroplasmic reticulum- endoplasmic reticulum
    5. T- tubule- an extension of the sarcolemma
       a. extends into the muscle fiber
       b. passes impulses to sarcoplasmic reticulum
    6. myofibril- a bundle of microfilaments that contract
    7. microfilaments- actin and myosin filaments whose structure and
       function account for muscle contractions and striations

  B. Myofibrils- cylindrical, run length of the muscle fiber

    1. sarcomere- contractile unit of a muscle fiber consisting of two kinds of
       a. Actin filament (thin filament)
          1. actin proteins with troponin and tropomysin attached
       b. Myosin filament (thick filament)
          1. contains numerous myosin filaments- shaped like a golf club
      c. Z disk- protein fibers to which actin filaments are attached
         1. sarcomere runs form one Z disk to another
      d. A band- dark region where actin and myosin filaments overlap
      e. I band- where only actin filaments exist
      f. H band- where only myosin filaments exist

    Myosin filaments slide along actin filaments allowing the sarcomere to
    contract (The H zone disappears)

  C. Innervation     Fig 6.9

    1. Muscle fibers are innervated by motor neurons
    2. Motor unit- a motor neuron and all the muscle fibers innervated by it
    3. Neuromuscular junction-
       a. Axon bulb- end of motor neuron
       b. synaptic cleft- separates bulb from sarcolemma

  D. Muscle contraction        Fig 6.6, 6.7, 6.8
    1. Nerve impulse travels down neuron and arrives at bulb
       a. triggers release of a neurotransmitter
          1. acetylcholine (ACh)
    2. ACh binds to proteins on the sarcolemma
    3. generates “impulse” that travels down sarcolemma and into T-tubules
    4. Stimulus triggers Ca2+ release from sarcoplasmic reticulum
       a. Ca2+ floods into the sarcoplasm
    5. Ca2+ binds to troponin molecules on the actin filament
       a. causes tropomysin molecules to move exposing binding sites on actin
    6. Head of myosin filament binds to active site of the actin (cross bridge)
       a. ATP allows the head of myosin filament to bend and reattach to a
          new site on the actin filament
    6. Sarcomeres (and subsequently the myofibrils) contract

  See Table 6.2

III. Whole Muscle Contraction

  A. Laboratory Observations

    1. myogram- visual pattern of the mechanical force of contraction
    2. Muscle twitch- complete cycle of muscle contraction and relaxation
       Fig 6.10
       a. latent period
       b. contraction period
       c. relaxation period

    3. Muscle must reach a threshold stimulus to contract
       a. summation- as stimulation frequency increases, muscle contraction
          increases in intensity
       b. tetanus- sustained muscular contraction
          1. continues until fatigue

  B. Recruitment and Strength Contraction
    1. each motor neuron will stimulate several muscle fibers (motor unit)
    2. may vary from few to 1000’s
    3. fine motor control comes from motor units that stimulate fewer fibers

IV. Energy for Muscle Contraction Table 6.1

A. Quick Sources of Energy:

  1. Stored ATP
     a. stored in very limited amounts

  2. Stored Creatine Phosphate
     a. stored in a resting muscle
     b. immediate form of ATP

  2. Stored Glycogen (Glycolysis of glucose)
     a. Anaerobic Respiration
        1. makes 2 ATP
        2. Lactate (toxin)

Slower Source of Energy:
  3. Stored Glycogen (aerobic breakdown of glucose)
     a. Aerobic Respiration
        1. 36 ATP/glucose molecule

B. Oxygen- Two sources:
  1. myoglobin- Oxygen carrier similar to hemoglobin
     a. stored in muscle cells
  2. oxygen from hemoglobin in RBC’s

C. Athletics and Muscle Contraction

  1. Exercise
     a. atrophy- decrease in size of muscles that are not used
     b. hypertrophy- increase in size of muscle fibers due to an increase in the
        number of myofibrils

  2. Muscle Stimulation and Contraction-
     a. electrical stimulus can cause muscle contractions- twitch
     b. increase frequency of stimulus and contraction may summate
        1. can cause tetanus!

  3. Types of Fibers-
     a. fast twitch muscle fibers-
        1. anaerobic muscles, quick energy, fatigue easily
     b. slow twitch muscle fibers-
        1. aerobic muscles, resistant to fatigue, endurance muscles

V. Cardiac Muscle and Smooth Muscle

  A. both are involuntary
    1. contract without nervous stimulation
       a. thru gap junctions
    2. stimulated by nerves as well
       a. autonomic nervous system
          1. stimulatory/inhibitory
    3. cardiac muscle is moderate in speed of contraction
    4. smooth muscles are slow
       a. actin/myosin filaments are arranged in a net like pattern over a
          smooth muscle cell       Fig 6.13
       b. contraction means shorter/fatter cell

VI. Comparing Muscle Types        Table 6.3- KNOW!

VII. Muscular Disorders and Diseases

  A. Disorders-
  1. Strain- over stretching of a muscle near a joint

  2. Sprain- twisting of a joint, injury to tendons, muscles, ligaments, blood
     vessels, nerves

  3. Myalgia- inflammation of muscle

  4. Tendonitis- inflammation of the tendon

  5. Muscle cramps- due to K imbalances?

B. Diseases-

  1. tetanus- (lockjaw)
     a. bacterial infection that causes muscle to lock into place
        1. due to toxin

  2. Muscular Dystrophy-
     a. diseases that cause progressive degenerative weakening of muscles.
        1. genetic

  3. Myasthenia Gravis-
     a. autoimmune disease
        1. immune system destroys acetylcholine receptors
        2. muscles no longer function properly

  4. Faciitis- inflammation of the facia
     (connective tissue that surrounds a muscle)

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