Muscle Types

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Muscle Types

• There are 3 types of muscles
• Skeletal muscle skeletal movement
• Cardiac muscle heart movement
• Smooth muscle peristalsis
• (pushes substances through hollow tubes)

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Skeletal Muscles (focus)

• Major Functions
• 1. movement
• 2. maintain posture
• 3. stabilize joints
• generate heat
• facial expressions

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• Characteristics
• 1. excitability (irritability) ability to
  respond to a stimulus (usually a
  neurotransmitter)
• 2. contractility the ability to shorten when
  adequately stimulated
• 3. extensibility the ability to be stretched
  muscles can be stretched beyond their normal
  resting length when relaxed
• 4. elasticity the ability of a muscle fiber to
  resume its resting length after being stretched

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• Connective Tissue Wrappings
• (external to deep)
• 1. epimysium layer of connective tissue that
  surrounds the entire muscle blends into tendons
• perimysium connective tissue extending inward
  from epimysium and separates muscle tissue into
  compartments called fascicles
• fascicles groups of muscle fibers (cells)
• 4. endomysium a sheet of connective tissue that
  surrounds each muscle fiber (myofiber)

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• Nerve and Blood Supply
• 1. Each skeletal muscle fiber is innervated
• 2. Muscle tissue is vascular

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• Parts of Muscle Fibers - Muscle Cell Organelles
• a. sarcolemma plasma membrane of muscle cell
  surrounds myofibers
• b. sarcoplasm similar to cytoplasm contains
  large amounts of glycogen for energy

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• c. sarcoplasmic reticulum similar to
  endoplasmic reticulum of cells stores and
  releases Ca2 on demand when muscles are ready to
  contract
• transverse tubules (t-tubules) channels that
  carry nerve impulses (action potentials) deep
  into the muscle cell
• mitochondria - muscle cells have many for energy

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• Myofibrils
• rod-like fibers that run parallel to the muscle
  cell
• Hundreds to thousands in a muscle fiber
• composed of striations repeating series of dark
  and light bands
• What causes those striations?
• The arrangement of myofilaments!

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Structure of Myofilaments

• The thick filaments are primarily made of myosin.
• The thin filaments primarily contain actin.
• Thin filaments also contain tropomyosin
  troponin.

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View of myofilaments

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• Striation Pattern
• A band dark appearance, made of primarily of
  thick filaments (myosin) some thin filaments
  (actin)
• I band light appearance, made of thin filaments
• Z line (disc) connects each myofibril to the
  next throughout the width of the muscle fiber Z
  line to Z line is one sarcomere the smallest
  functional unit of a muscle contraction
• H Zone holds thick filaments together, only
  visible when the muscle fiber is relaxed

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(Arranged From Largest to Smallest)

• Muscle (organ)
• Fascicles
• Muscle cell
• Myofibril
• Myofilaments

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• Contraction of Skeletal Muscle Cells
• One motor neuron (nerve cell) may stimulate a few
  muscle cells or hundreds.
• A motor neuron all the myofibers a motor unit
• When an axon of a nerve cell reaches a muscle
  cell it branches into a number of axon terminals.
• Each axon terminal forms junctions with
  sarcolemma of different muscle cells
  (neuromuscular junction - NMJ).
• Although they are very close the axon and
  sarolemma do not touch directly this is a
  synaptic cleft.

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A Blast from the past . . .Active Transport!

• Sodium / potassium pump, maintains cell resting
  potential at -70mV (charge inside a cell) a
  change is this charge 30mV will cause an action
  potential
• (nerve impulse)

2 K in for every 3 Na out
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Actions Occurring At NMJ Web animations
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• An action potential travels along an axon to an
  axon terminal.
• This stimulates the release of the
  neurotransmitter acetylcholine or ACh from
  synaptic vesicles.
• ACh diffuses across the synaptic cleft and
  attaches to ACh receptors on the sarcolemma of a
  muscle fiber this region is known as the motor
  end plate.
• The ACh receptors open channels on the motor end
  plate which allows Na to diffuse into the muscle
  cell.
• This change in charge in the muscle cell allows
  for the action potential to continue and move
  deep into the muscle cell via the transverse
  tubules.

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• An action potential passes into the muscle cells
  via t-tubules (transverse tubules)
• This stimulates the release of Ca2 from the
  sarcoplasmic reticulum
• Ca2 binds to the troponin / tropomyosin complex
  and allows myosin heads to bond to actin and push
  thin filaments toward the center of the sarcomere
• This process requires ATP

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Contraction of a Skeletal Muscle

• Muscle fiber contraction is all or none
• Not all fibers may be stimulated during the same
  interval
• Different combinations of muscle fiber
  contractions differing responses

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Graded responses different degrees of skeletal
muscle shortening
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Types of Graded Response

• Twitch
• Single, brief contraction
• Not a normal muscle function

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Types of Graded Response

• Unfused (incomplete) tetanus
• Some relaxation occurs between contractions
• The results are summed

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Types of Graded Response

• Fused (complete) tetanus
• No evidence of relaxation before the following
  contractions
• The result is a sustained muscle contraction

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Muscle Response to Strong Stimuli

• Muscle force depends upon the number of fibers
  stimulated
• More fibers contracting results in greater muscle
  tension
• Muscles can continue to contract unless they run
  out of energy

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Types of Muscle Contractions

• Isotonic contractions
• Myofilaments are able to slide past each other
  during contractions
• The muscle shortens
• Isometric contractions
• Tension in the muscles increases
• The muscle is unable to shorten

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Effects of Exercise on Muscle

• Aerobic or Endurance
• result in stronger muscles due to increase blood
  supply
• Muscle fibers increase mitochondria and oxygen
  storage
• Muscle becomes more fatigue
• resistant
• Heart enlarges to pump
• more blood to body
• Does not increase skeletal
• muscle size

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Resistance or Isometric Exercises

• Results of increased muscle use from resistance
  training
• Individual muscle cells make more contractile
  filaments connective tissue increases
• Increase in muscle size
• Increase in muscle strength

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• How do all of our muscles get the
• energy they need for contractions?

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Energy for Muscle Contractions

• Initially, muscles used stored ATP for energy
• Bonds of ATP are broken to release energy
• Only 4-6 seconds worth of ATP is stored by
  muscles
• Then, other pathways must be utilized to produce
  ATP

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1. Direct Phophorylation

• Muscle cells contain creatine phosphate (CP)
• After ATP is depleted, ADP is left
• CP transfers energy to ADP, to regenerate ATP
• CP supplies are exhausted in about 20 seconds

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2. Aerobic (Cellular) Respiration

• Occurs in the mitochondria
• Glucose is broken down to carbon dioxide and
  water, releasing energy
• Slower reaction that requires continuous oxygen

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3. Anaerobic Glycolysis

• Reaction that breaks down glucose without oxygen
• Glucose is broken down to pyruvic acid to produce
  some ATP
• Pyruvic acid is converted to lactic acid
• Not as efficient, but is fast
• Huge amounts of glucose are needed
• Lactic acid produces muscle fatigue

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• Muscle Fatigue
• When a muscle is fatigued, it is unable to
  contract
• The common reason for muscle fatigue is oxygen
  debt
• Oxygen must be repaid to tissue
• Oxygen is required to get rid of accumulated
  lactic acid
• Increasing acidity (from lactic acid) lack of
  ATP causes the muscle to contract less