Muscular System

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					Muscular System


      Chapter 8
     What are functions of the
        muscular system?
1. Gross body movement
2. Stabilizing body positions – “Tone”
3. Generate heartbeat
4. Movement substances within the
   body
5. Regulating organ volumes
6. Producing body heat
 Properties of Muscle Tissue
1. Electrical Excitability – able
   to respond to stimuli and send
   an impulse
2. Contractility – ability to
   contract forcefully, muscle
   body shortens
3. Extensibility – ability to
   stretch
4. Elasticity – ability to return
   to original length or shape
What are the 3 types of
    muscle tissue?

        Skeletal
        Smooth
        Cardiac
      Skeletal Muscle
Characteristics:
 * Multinucleated
 * Striated
 * Voluntary control
Appearance:
        Smooth Muscle



                •Location: Internal organs, blood vessels
                •“Peristalsis” movement of digestive tract
Uninucleated
cells           •Usually organized into two sheet-like layers:
                        longitudinal and circular
Involuntary     •Two types: Visceral and Multiunit
No striations
                  Cardiac
• Striated and uni-
  nucleated
• Branching cells
• Intercalated discs
  separate cells
• Rhythmicity
• Only found in wall
  of heart
• Self-exciting
  tissue
• Large transverse
  tubules
Aponeurosis, Fascia and
       Tendons
       • Fascia – “gift
         wrap” around
         muscle body or
         found under
         skin (spider webs)
       • Tendons -
         connect
         muscle to bone
       • Aponeurosis –
         flat and sheet-
         like tendon
         connects
         muscle to CT
Skeletal Muscle Anatomy
    The Muscle Fiber Structure
• Sarcolemma
• Sarcoplasm
• Nucleus(i)
• Sarcoplasmic
  reticulum
• Mitochondria
• Myofibrils
  1. Actin (thin)
  2. Myosin (thick)
Skeletal Muscle Fiber Structure
Anatomy of a Myofibril
               The Sarcomere!
Sarcomere: Single contracting unit within a myofibril.
Striation pattern is caused by the organization of the
  myofilaments
• Length = Z line to Z line
• I band = only actin region          Contraction: Z-line
• A band = myosin and actin region moves towards M
                                      line
• H zone = only myosin region
• M line = center of H zone
Muscle Body
  Fascicles     Largest
                   to
Muscle Fibers   Smallest
 Myofibrils
Myofilaments
Now that you are familiar
with muscle anatomy, what
   is the physiology of
       contraction?

     How does muscle
   contraction happen?
         Section 8.3
Structures Involved
    in Contraction
Motor Unit:
 One neuron and all
 the muscle fibers it
 connects with.

Stronger contractions
  have more motor
  units activated.
The Neuromuscular Junction: where the
  neuron meets with the muscle fiber.
Sarcomere – smallest contracting
             unit
 The Sliding Filament Theory




                                        Video:
                                      “Sarcomere
                                      shortening”




Now, look at how this process really works…
               Muscle Contraction
1.   Impulse reaches synaptic
     bulb.
2.   Calcium channels open and
     calcium enters.
3.   Ca causes vesicles to
     migrate to cell membrane to
     release neurotransmitter
     (Acetylcholine = Ach).
4.   Vesicles fuse with
     membrane and release Ach        Video
     into synaptic cleft (gap).
5.   Ach diffuses across the
     cleft.
6.   Ach binds with receptor
     proteins on motor end plate.
7.   Motor end plate depolarizes.
8.   Action potential is generated
     in muscle cell.
            9. Action Potential moves:
               • along the sarcolemma
               •down the transverse tubules
Animation      •into the sarcoplasmic reticulum
            10. Calcium is released from the sarcoplasmic
            reticulum.
Binding site before and after
calcium reaches myofilaments.



                                    VIDEO




Troponin/tropomyosin complex pulled away by
        calcium so myosin can bind!
      12.

        VIDEO 1

            Video 2




                      13.

11.
       Relaxation phase…
1. Acetylcholine esterase decomposes Ach
   and removes it from synaptic gap.
2. ATP binds to myosin causing linkage to
   release from actin.
3. Actin and myosin filaments slide apart.
4. Calcium ions are actively transported
   back into the sarcoplasmic reticulum.
5. Muscle fiber relaxes.
            Section 8.4



How does the muscle fiber
     get ATP for the
      contraction?

       • Cell Storage
     • Creatine phosphate
    • Cellular respiration or
          fermentation
            Creatine Phosphate
• Used when current cell
  supply of ATP runs out.
  (within 6 sec.)
• Cannot be used
  directly as an energy
  source.
• Purpose: to transfer
  stored energy to ADP
  to make ATP.
• Creatine supply is
  exhausted in 30 sec.
• Activities that benefit:
  100 meter dash and
  weight lifting
           Aerobic Respiration

• With oxygen
  available,
  glucose is
  converted into
  the max amount
  of ATP!
Myoglobin:
  Oxygen-binding
  pigment found
  only in muscle
  cells.
  What if you run out of
         oxygen?
Anaerobic respiration occurs by fermentation.
Fermentation produces Lactic Acid.
Lactic acid is carried to liver to be converted
back to glucose.
Low intensity or moderate exercise can recycle
the lactic acid immediately. (not a lot is
produced)
Good energy source for “stop and go” sports.
      (soccer, tennis, short-term swimming)
            Oxygen Debt
• The amount of O2 liver cells require to
  convert the lactic acid into glucose +
  the O2 muscle cells require to restore
  stored ATP and creatine phosphate.
• Training can speed up the process.
O2 Muscle need + O2 Liver need = Oxygen Debt
For most activities, all systems are used. It’s just
the percentages differ based on the intensity of
                    the activity.

            % Creatine     % Lactic     % Aerobic
Activity
            Phosphate       Acid        Respiration

 Sprint          95            3             2

  Mile           15            55            30

Marathon         5             5             90
             Muscle Fiber Types
             Slow Twitch                        Fast Twitch
  •    Not easily fatigued           •   Easily fatigued
  •    Myoglobin – “red”             •   Little myoglobin – “white”
  •    Use in low intensity          •   Used in high intensity
                                         activities – Anaerobic
       activities – Endurance!           Power!
  •    Not a lot of growth – Lean    •   Increase filaments with
  •    Lots of mitochondria              use – Hypertrophy!
                                     •   Can be irreversibly
                                         changed into slow twitch!
Slow                         Fast

                                    Genetically, most people are
                                     50% slow, 50% fast twitch
What if the muscle
 cannot contract
    anymore?
              Muscle Fatigue
• Loss of the ability to contract
• Causes:
  1. Lactic acid buildup, pH drops
  2. Blood supply interruption
  3. Lack of acetylcholine
  4. Lack of ATP

• Cramps: sudden, involuntary contractions or
  spasms in one or more of your muscles.
  Possible causes: lack of ATP, dehydration or electrolyte imbalance
     Muscular Responses
• Threshold stimulus – minimum
  amount of stimulus (Ach) needed to
  cause a contraction.
• All-or-None Response – a muscle
  fiber will always fully contract no
  matter the strength of the stimulus.
  If the minimum amount of stimulus
  is not met, no contraction will occur.
Muscle contractions can be
measured and recorded by:


     The Myogram
  Twitch: A single contraction of a
  muscle fiber.
Myogram Recording




(Latent)
a)   Shows a series of
     twitches with
     complete
     relaxation before
     the next stimulus.


b)   Summation
     another stimulus
     comes before
     complete
     relaxation can
     occur, thus
     increasing the
     contraction force.

c)   Tetanus:
     Stimulus is held
     constant, where
     there is no
     relaxation.
             Recruitment
• Stimulating more motor units in a muscle body to
  contract.
• A greater force applied to the muscle or increase
  the frequency of stimuli will cause this.


               Muscle Tone
• Skeletal muscle fibers constantly being
  stimulated by brain. (involuntary)
• Stretch receptors in muscles monitor muscle
  health.
• Loss of posture tone = collapse
          How Do I
    Hypertrophy My
1.
           Muscles?
    Do high intensity activities.
2. Use the fast-twitch muscles.
3. Eat protein for building material.
4. Maintain activity or else: atrophy

By age 80, there is a 50% decrease in muscle
    strength!

				
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posted:9/17/2011
language:English
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