Chapter 9 Muscles

1
Chapter 9 Muscles
2
Muscles

• A Skeletal Muscle is a complete organ unto itself
  and belongs to the muscular system.
• Muscles attach to bones and other muscles via
  Tendons.
• Muscles are kept in separate from their
  neighboring muscles by layers of dense connective
  tissue called Fascia.

3
Muscles

• Connective Tissue Coverings
• Epimysium tough outer covering of connective
  tissue that covers an entire muscle.
• Perimysium separates and surrounds fascicles
  (bundles) of muscle fibers from each other.
• Endomysium separates and surrounds each
  individual muscle fiber.

4
Figure 09.02
5
Muscles

• A skeletal muscle fiber is a single muscle cell
  that contains many myofibrils. Myofibrils
  consist of two kinds of protein filaments called
  Myosin (thick filaments) and Actin (thin
  filaments).
• Troponin and Tropomyosin are proteins associated
  with the Actin filament.

6
Muscles

• Troponin and Tropomyosin are two protein
  filaments associated with the actin filament.
  Tropomyosin occupies the longitudinal groove on
  the actin fiber covering its binding site.
  Troponin binds tropomyosin in place until told to
  release for muscle contraction.

7
Figure 09.06
8
Muscles

• Skeletal Muscle Contraction
• The Neuromuscular Junction (NMJ) is the site
  where a motor neuron meets a muscle fiber. The
  axon of the motor neuron comes very close to the
  Motor End Plate of the muscle fiber. The space
  between the axon and the muscle fiber is called a
  Synapse.

9
Muscles

• Communication between the neuron and the muscle
  fiber is accomplished via Neurotransmitters.
  Neurotransmitters are substances that bind with a
  receptor site on the motor end plate and give a
  stimulus. This stimulus is usually for muscle
  contraction.
• Neurotransmitters are synthesized in the
  cytoplasm of the motor neuron and stored in
  synaptic vesicles near the end of the axon.
• Acetylcholine (Ach) is the most common of
  neurotransmitters used for skeletal muscle
  contraction.

10
Muscles
11
Muscles

• Ach is released from the axon upon a neural
  impulse reaching the end of the axon. Ach then
  quickly diffuses across the synaptic cleft and
  binds with specialized receptors on the motor end
  plate. This stimulates a muscle impulse.
• The muscle impulse changes the charge on the
  interior of the muscle fibers cell surface.
  This change in charge is ultimately responsible
  for the contraction of the muscle fiber.

12
Muscles

• Upon the fiber achieving impulse, the cisternae
  in the sarcoplasmic reticulum become more
  permeable to calcium ions and consequently these
  ions move into the cytosol of the fiber.
• Once in the cytosol the calcium ions begin to
  bind to the troponin molecules causing a change
  in their shape. This shape change thereby makes
  the troponin molecules move in relation to
  tropomyosin. This causes the tropomyosin to move
  away from the binding site on the actin molecule.
  Actin and myosin are now free to bind with each
  other.

13
Muscles

• The heads of the myosin cross bridges are
  cocked in response to the presence of ATP
  molecules in the area. Once myosin goes into
  action, with the heads of its cross bridges
  binding to the actin binding site, myosin pulls
  on the actin filament bringing it back to its
  neutral state.
• ATPase is an enzyme contained in the heads of the
  myosin cross bridges that is used to cause the
  breakdown of ATP to ADP and release the energy
  used for the cocking of the myosin heads.

14
Muscles

• The actin fibers are thus caused to slide past
  the myosin fibers with each cocking, binding,
  pulling, and releasing of the myosin cross
  bridges. This action is repeated many times over
  to cause the full contraction of a muscle fiber.

15
Muscles
16
Muscles

• Energy Sources
• ATP is stored in the muscle fibers for quick
  availability. However, only a small amount is
  kept at the ready.
• ATP can be quickly synthesized by the use of
  Creatine Phosphate which will phosphorylate ADP
  into ATP (ADP P).
• Once creatine phosphate is exhausted the fiber
  must turn to Cellular Respiration of glucose to
  provide fuel for muscle contraction.

17
Muscles

• Types of Cellular Respiration
• Anaerobic Respiration involves the production of
  ATP in an environment where oxygen is not needed.
  One pathway of this method is called Glycolysis.
  Glycolysis takes place in the cytoplasm and
  involves the breakdown of a molecule of glucose
  into two smaller parts called pyruvic acid. The
  energy released in the breaking of the covalent
  bond releases energy which is ultimately
  harnessed to phosphorlyate ADP into ATP. This
  method is not very efficient and is slow to
  garner any significant product.

18
Muscles

• Aerobic Respiration involves the production of
  ATP using oxygen as a catalyst to transfer energy
  and bring about the phosphorlyation of ADP into
  ATP. This takes place in the mitochondria,
  requires oxygen, and is much more efficient than
  most anaerobic methods.

19
Muscles

• Oxygen Debt is a result of a build up of excess
  waste products in a cell. These waste products
  must be cleared from the cell, usually via
  exocytosis, before the cell can resume optimal
  operations.
• Muscle Fatigue is usually due to prolonged use
  via contraction, and involves the build up of
  lactic acid (a waste product) in the muscle cells
  from anaerobic ATP production. p.297
• Heat production is due to cellular respiration.
  Much of the energy released from the breakdown of
  bonds between atoms is released as heat.

20
Muscles

• In order to cause a muscle fiber to contract the
  stimulus that the fiber receives must reach
  Threshold Stimulus. This is the minimum amount
  of stimulus that the fiber must receive to cause
  a muscle impulse.
• All muscle fibers must obey the All or None
  Principle. This principle states that when a
  muscle fiber generates a muscle impulse, it will
  contract to 100 of its capability or it will
  not contract at all.
• Muscle Tone is determined by the amount of
  sustained contraction a muscle has while in a
  relaxed phase.

21
Muscles

• Types of Contractions
• Isotonic in this type of contraction the muscle
  changes in length while undergoing contraction.
• Concentric shortening in length while
  contracting as if lifting an object
• Eccentric lengthening while contracting as if
  in laying an object down. Some times called
  Negatives.

22
Muscles

• Isometric in this type of contraction the
  muscle length does not change. The fibers
  contract and tension builds, but the overall
  length of the muscle does not change. Used most
  of the time to reinforce posture and hold us
  upright.

23
Muscles

• Slow Twitch Fibers (Type I) are also called red
  fibers as they are oxidative and are resistant to
  fatigue. They are called red fibers as they
  contain myoglobin which stores oxygen. They also
  have many mitochondria which utilize the oxygen
  in aerobic respiration.
• Fast Twitch Fibers (Type II) may be primarily
  oxidative or primarily glycolytic and are
  referred to as white fibers as they contain less
  myoglobin than red fibers. They are therefore
  not as well vascularized and fatigue more easily
  than red fibers.

24
Muscles

• Fast twitch fatigue resistant fibers are also
  called Intermediate Fibers or Type IIb fibers.
  They combine the fast twitch capability of white
  fibers with fatigue resistance associated with
  red fibers.

25
Muscles

• Smooth Muscle
• Visceral smooth muscle is responsible for
  Peristalsis. These cells are held in close
  contact with each other by gap junctions. When
  one cell is stimulated the neighboring cells next
  to it may be stimulated due to the presence of
  gap junctions. This leads to the rythmic
  contractions of peristalsis. This kind of
  contraction is commonly found in the hollow
  tubular organs found in the digestive system and
  parts of the urinary and reproductive systems.

26
Muscles

• Stretch receptors found in the walls of some
  organs can also cause these cells to contract
  when they are stimulated by distension.
• Smooth muscle is slower to contract and relax
  than skeletal muscle, but is able to hold its
  contractions longer with the same amount of ATP.

27
Muscles

• Cardiac Muscle
• Found only in the heart, cardiac muscle is
  involuntary and contain many mitochondria. This
  allow them to undertake strenuous activity for
  prolonged periods of time.
• Cardiac muscle cells are held together by special
  cellular adhesions called Intercalated Discs.
  These specialized structures allow for rapid cell
  to cell communication and make possible the
  rythmicity that this organ is known for.

28
Muscles

• The Origin of a muscle is the immovable or stable
  end. The origin is typically proximal to the
  insertion.
• The Insertion of a muscle is the moveable or
  mobile end. The insertion is typically distal to
  the origin.

29
Muscles

• Actions of muscles
• A Prime Mover (or Agonist) is a muscle that is
  primarily responsible for producing a movement.
• An Antagonist is a muscle that opposes a prime
  movers action.
• Note These type of relationship between two
  muscles will usually reverse itself when another
  type of movement is produced.

30
Muscles

• Synergists are muscles that assist the prime
  mover. They add power, stability, and
  coordination to the contraction of the prime
  mover.
• Fixators are muscles that fix a joint in
  position. They are typically used for posture.