Chapter 8

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					Chapter 8
Muscular System
        Bell work:
    November 5, 2010

What is the function of
 the muscular system?
        Muscular System
Organs: Muscle tissue
(skeletal, smooth, and

Function: Moves bones at
joints and pushes
substances such as blood,
food, and fluids throughout
the body.
          8.1 Introduction
- All movements
  require muscle
  which are organs
  using chemical
  energy to
- 3 types of muscle:
  skeletal, smooth,
  and cardiac
 Introduction to the
Muscular System Video
          Bell work:
      November 8, 2010

 What are the two kinds of
protein filaments that make up
          a myofibril?
          Bell work:
      November 8, 2010

Myosin (thick protein filament)
    and Actin (thin protein
 8.2 Structure of Skeletal Muscle

- By weight, human
  body is ~ 40%
  skeletal muscle
- Each muscle is an
  organ, comprised
  of skeletal muscle
  tissue, connective
  tissues, nervous
  tissue, and blood
          Connective Tissue Coverings

• Layers of dense
  connective tissue, called
  fascia, surround and
  separate each muscle.
• Tissue extends beyond
  the ends of the muscle
  and gives rise to tendons
  that are fused to the
  periosteum of bones.
          Connective Tissue Coverings

- The layer of connective
  tissue around each whole
  muscle is the
  epimysium; the
  perimysium surrounds
  individual bundles
  (fascicles) within each
  muscle; and each muscle
  cell (fiber) is covered by
  a connective tissue layer
  called endomysium.
                 Skeletal Muscle Analogy
    Pretend you are going to play a
    joke on someone and give them
    100 pencils. The pencils will
    represent muscle fibers.
-   First you wrap each individual
    pencil in tissue paper (dense
    tissue paper of course!). This
    would be endomysium.
-   Then you take about 10 pencils
    in a bundle (a fascicle) and wrap
    them in paper (perimysium).
-   After that you take all the
    bundles and wrap them in gift
    wrap (epimysium).
-   But you are going to mail this
    joke, so you also have to wrap it
    in brown paper representing the
             Skeletal Muscle Fibers

- Each muscle fiber is a
  single, long, cylindrical
  muscle cell.
- Beneath the sarcolemma
  (cell membrane) lies
  sarcoplasm (cytoplasm)
  with many mitochondria
  and nuclei; the
  sarcoplasm contains
           Skeletal Muscle Fibers

- Thick filaments of
  myofibrils are made
  up of the protein
- Thin filaments of
  myofibrils are made
  up of the protein
- The organization of
  these filaments
  produces striations.
          Skeletal Muscle Fibers (Cells)

• A sarcomere extends
  from one Z line to the
• I bands (light bands)
  made up of actin
  filaments are anchored to
  Z lines.
• A bands (dark bands)
  are made up of
  overlapping thick and thin
• In the center of A bands
  is an H zone, consisting
  of myosin filaments only.
       Neuromuscular Junction
• The site where the
  motor neuron and
  muscle fiber meet is
                  Motor Units
• A motor neuron and
  the muscle fibers it
  controls make up a
  motor unit; when
  stimulated, the
  muscle fibers of the
  motor unit contract all
  at once.
             Bell work:
         November 9, 2010
Label the missing pieces of the picture.
   8.3 Skeletal Muscle Contraction
- Muscle contraction involves shortening of
sarcomeres, and pulling of muscle against its
         Role of Myosin and Actin
• Myosin - two twisted strands with cross-bridges
  projected outward along the strands.
• Actin - protein with myosin binding sites;
  tropomysosin and troponin are two proteins
  associated with the surface of the actin filaments.

  • Cross-bridges of myosin filaments form linkages with actin
       Sliding Filament Theory
• Myosin (thick) filaments combine with Actin (thin)
  filaments, forming actomyosin
• Filaments slide past each other
• Reaction between actin & myosin generates force of
        Stimulus for Contraction
• The motor neuron
  release neurotransmitter
  acetylcholine from
  synaptic vesicles into the
  synaptic cleft to initiate
  muscle contraction.
• Protein receptors in the
  motor end plate detect
  the neurotransmitters,
  and a muscle impulse
  spreads over the surface
  of the sarcolemma and
  into the T tubules, where
  it reaches the
  sarcoplasmic reticulum.
        Stimulus for Contraction
- Muscle impulse signals
  sarcoplasmic reticulum
  to release calcium ions.
- The high concentration
  of calcium in the
  sarcoplasm interacts with
  the troponin and
  tropomyosin molecules,
  which move aside,
  exposing the myosin
  binding sites on the actin
       Stimulus for Contraction
- Myosin cross-bridges now
  bind and pull on the actin
  filaments, causing the
  sarcomeres to shorten.
- Acetylcholinesterase
  breaks down
- Calcium returned to the
  sarcoplasmic reticulum,
  linkages between myosin
  & actin are broken.
• Myosin
  (thick) &
  Actin (thin)
  slide past
  each other
• Z-lines
• A-Bands
   Energy Sources for Contraction
 - ATP supplies the energy
   for muscle fiber
- Creatine Phosphate,
   stores energy that can be
   used to synthesize (put
   together) ATP
- ATP is also needed for
   muscle relaxation
         Oxygen Supply & Cellular
• Muscle has high
  requirement for oxygen
• Hemoglobin in red blood
  cells carries oxygen to
• The pigment myoglobin
  stores oxygen in muscle
    Bell work:
November 10, 2010
What is a twitch?
         Bell work:
     November 10, 2010

A contraction of a muscle fiber
     followed by relaxation.
                 8.3 continued…
                  Oxygen Debt
- During rest or moderate activity,
  muscles receive enough oxygen
  to respire aerobically
- During stenuous exercise,
  oxygen deficiency may cause
  lactic acid to accumulate.
- Oxygen debt = amount of
  oxygen required to convert
  accumulated lactic acid to
  glucose and to restore supplies of
  ATP and creatine phosphate.
           Lactic Acid
- Forms when there aren't enough oxygen
  molecules to completely breakdown the
  glucose (sugar) in the body.
- Clears out shortly after exercise stops.
                  Muscle Fatigue
- Fatigue: when a muscle loses
  its ability to contract during
  strenuous exercise
- Arises from accumulation of
  lactic acid in the muscle.
- Lowered pH due to lactic acid
  build up prevents muscle from
- Muscle cramp: lack of ATP
  required to return calcium ions
  back to the sarcoplasmic
  reticulum so muscle fibers can
              Heat Production
- Contraction of skeletal muscle is
  important source of heat for
- During muscle contractions,
  muscle cells expend much
  energy, most of which is
  converted to heat.
- Cellular respiration releases
  heat as a byproduct (which is
  another source of heat for the
      8.4 Muscular
- Myogram: measures
  muscle activity
- Threshold Stimulus:
  A muscle fiber
  unresponsive to
  stimulation unless
  the stimulus is of a
  certain strength
         All-or-none Response
- When muscle fiber
  contracts, it
  contracts to its full
  extent or not at all.
- It cannot contract
 - Twitch - A single,
   short contraction
   involving only a few
   motor units
- Latent Period: Time
   delay between when
   stimulus is applied
   and when muscle
- Latent Period =
   less than two
- Followed by period
   of contraction and
  period of
                  Motor Units
• A motor neuron and
  the muscle fibers it
  controls make up a
  motor unit; when
  stimulated, the
  muscle fibers of the
  motor unit contract all
  at once.
  Summation & Recruitment
- Recruitment: increase in number of activated
  motor units within muscle at higher intensities of
- Summation: the degree of contraction of a
 skeletal muscle is influenced by the number of
 motor units being stimulated
            Muscle Tone
- Achieved by a
  continuous state of
  sustained contraction
  of motor units within
  a muscle.
             Slow Twitch Fibers
• More efficient using oxygen to generate more fuel
  (ATP) for continuous, extended muscle contractions
  over a long time.
• Fire more slowly than fast twitch fibers and can go for
  a long time before they fatigue.
             Fast Twitch Fibers
• Better at generating short bursts of strength
• Fatigue more quickly.
• Produce same amount of force per contraction as
  slow, but are able to fire more rapidly (hence the
        Bell work:
    November 11, 2010
What are the 3 parts of a
      8.5 Smooth Muscles
- Elongated with tapered
  ends, lack striations
  and have a undeveloped
  sarcoplasmic reticulum
   2 Types of Smooth Muscle
1. Multiunit smooth
   - blood vessels and
   iris of eye, fibers
   separate rather
   than in sheets
    2 Types of Smooth Muscle

    2. Visceral Smooth
–     Sheets
–     found in the walls of
      hollow organs
–     fibers stimulate one
      another (rhythmicity)
–     responsible for
      peristalsis in hollow
      organs and tubes
 Smooth Muscle Contraction
- Myosin-binding-
to-actin mechanism
same for smooth
and skeletal
- Acetylcholine and
stimulate and
inhibit smooth
muscle contraction,
depending on the
target muscle.
  Smooth Muscle Contraction
- Smooth muscle is
slower to contract and
relax than skeletal
- Can contract longer
using the same amount
of ATP.
          Bell work:
      November 12, 2010
How does smooth muscle differ
    from skeletal muscle?
           Bell work:
       November 12, 2010
   Smooth muscle is elongated with
tapered ends, lacks striations and has
an undeveloped sarcoplasmic reticulum
         8.6 Cardiac Muscle
- Only found in heart
- Mechanism of
  contraction is almost
  same as skeletal and
  smooth muscle
- Branching, striated,
  cells interconnected
          8.6 Cardiac Muscle
• Intercalated disks - join
  cells and transmit the
  force of contraction from
  one cell to the next
• Aid in the rapid
  transmission of impulses
  throughout the heart
• Cardiac muscle is self-
  exciting and rhythmic
• Whole structure
  contracts as a unit.
  Inherited Diseases of Muscle
• Muscular Dystrophy –
  group of disorders that
  involve muscle weakness
  and loss of muscle
  – muscles weaken and
    degenerate over time
• Charcot-Marie-Tooth
  Disease – weakness in
  muscles of hands and
  feet, decreased tendon
  reflexes in those areas
  Inherited Diseases of Muscle
- Mytonic Dystrophy – delayed muscle
  relaxation following contraction
  - Facial/Limb weakness
- Hereditary Idiopathic Dilated
  Cardiomyopathy – Genetic error in actin
  of cardiac muscle
  - Prevents actin from trasmitting force of
  - Causes heart chambers to enlarge and fail
   8.7 Skeletal Muscle
Origin and Insertion
- The immovable
  end of a muscle is
  the origin, while
  the movable end
  is the insertion;
  contraction pulls
  the insertion
  toward the origin.
- Some muscles
  have more than
  one insertion or
 Interaction of Skeletal Muscles
- Prime Mover: the one doing most of the
- Synergists: Helper muscles
- Antagonists: Opposing muscles
                        Example: When
                        extending the forearm…
                        Triceps brachii (prime
                        Biceps brachii
              8.8 Major
           Skeletal Muscles

     Muscles are named according to:
size, shape, location, action, number of
   attachments, or direction of fibers
        8.8 Major
     Skeletal Muscles
Pectoralis Major – large, pectoral
Deltoid – triangle shaped
Extensor Digitorum – extends
Biceps brachii – 2 points of origin
  (biceps) in brachium (arm)
Sternocleidomastoid – attached to
  sternum, clavicle and mastoid
External Oblique – Near outside
  with fibers running obliquely
  (slanting direction)
            Bell work:
        November 15, 2010

What is an origin
   of muscle?
  What is an
          Bell work:
      November 15, 2010

Origin –
immovable end
of muscle
Insertion –
movable end of
      Muscles that Move the Pectoral
- The chest and
  muscles move
  the scapula.
- Major muscles
  include the
  major, levator
  anterior, and
           Bell work:
       November 19, 2010

How does
muscle differ
from skeletal
              Bell work:
          November 19, 2010

Cardiac muscle is
only found in the
heart and is
striated, and has
cells (intercalated
          Bell work:
      November 22, 2010
Sometimes muscles are connected
to each other by broad sheets of
connective tissue called…
     Bell work:
 November 22, 2010

an aponeurosis

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