Muscle Physiology: The Actions of the Sarcomere.

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Muscle PhysiologyThe Actions of the Sarcomere.
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• Cardiac Muscle
• Characteristics
• Intercalated disks
• Striated
• Involuntary
• Located in heart

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Skeletal Muscle

• Characteristics
• Many nuclei per cell
• Striated
• Voluntary
• Located along bones

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Smooth Muscle

• Nonstriated
• Involuntary
• Located in digestive tract

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Functions of Muscles

• Movement results from muscle contraction,
  enables you to respond quickly
• Maintains Posture and Joint Stability allows you
  to sit upright stabilize joints of the body
• Support Soft Tissue abdominal muscles protect
  underlying digestive organs.
• Guard Entrances and Exits
• Generate Heat heat is generated as they
  workFRICTION
• Maintains body temperature
• Skeletal muscles create the most heat

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Characteristics of Muscle Tissue

• Excitability ability to receive and respond to
  stimuli
• Contractibility ability to shorten quickly and
  with force
• Extensibility ability to be stretched or
  extended beyond their resting state
• Elasticity ability of a muscle fiber to recoil
  and resume its resting length

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Organization of Muscle

• Muscles are composed of groups of fibers called
  fasicles.
• Fibers are the muscle cells inside all muscle.
• Tendons are bands of collagen fiber that attach
  muscle to bone.

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Organization
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Sarcomere the Contracting unit
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Skeletal Muscle Striations
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Z line I band H band A band
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• Organization from the muscle fiber to the
  sarcomere.

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Cross sectional view of Sarcomere.
Differences are detected in the sizes of the
myofilaments Myosin is the thicker fiber. Actin
is the thinner fiber.
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Striations are seen because of sarcomere bands.
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Muscle fiber structure

• Muscle cell
• Sarcolemma
• Sarcoplasm
• Sarcoplasmic reticulum
• T tubule
• mitochondria

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Sliding Filament Theory
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Sliding Filament TheoryActin slides over myosin
shortening the sacromere between the Z lines
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Events at the Neuromuscular Junction
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Action potential arrives at axon terminal
of motor neuron.
Ca2
Ca2
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Voltage-gated Ca2 channels open and Ca2
enters the axon terminal.

Synaptic vesicle containing ACh
Mitochondrion
Axon terminal of motor neuron
Synaptic cleft
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Ca2 entry causes some synaptic vesicles
to release their contents (acetylcholine) by
exocytosis.
Fusing synaptic vesicles
ACh
Junctional folds of sarcolemma
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Acetylcholine, a neurotransmitter, diffuses
across the synaptic cleft and binds to
receptors in the sarcolemma.
Sarcoplasm of muscle fiber
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Events at the Neuromuscular Junction
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Cross Bridge Cycle (2 of 4)
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Cross Bridge Cycle (3 of 4)
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Cross Bridge Cycle (4 of 4)
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Steps of Muscle Contraction
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Steps of Muscle Contraction
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What happens at the sarcomere?
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Players for the power stroke

• Cross bridge attachment
• Power strokes
• Cross bridge detachment
• Cocking of the myosin head

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Power stroke
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Motor Unit A motor neuron and all the muscle
fibers it stimulates.
Atrophy- when muscle fibers become weaker and
smaller due to lack of stimulation by a motor
neuron.
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Muscle Tension

• The amount of tension produced by a muscle is
  determined by
• The frequency of muscle stimulation.
• The number of muscle fibers activated.
• 3. Degree of stretch by sarcomere.
  (length-tension relationship
• Myogram a graph that measures tension
  developing in a muscle fiber.

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Diagram of a Muscle Twitch
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Increase in muscle tension due to continued
stimulation.
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Muscle that reaches peak tension during rapid
cycles of contraction and relaxation.
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Complete tetanus relaxation state is eliminated.
Recruitment multiple motor unit summation
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Relationship between stimulus intensity and
muscle tension.
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Label the following!
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Muscle Metabolism

• Muscle stores limited reserves of ATP 4-6
  Seconds
• 3 Pathways for Generating ATP
• Production of ATP from Creatine phosphate
• Aerobic Respiration
• Anaerobic Respiration

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Aerobic Muscle Metabolism

• Glycolysis
• Aerobic Respiration
• Krebs Cycle
• ETC

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Anaerobic Muscle Metabolism

• Oxygen Debt
• Lactic Acid Fermentation
• Muscle Fatigue

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Creatine Phosphate
Muscle cells store 2-3 times creatine as
ATP. Stored ATP and CP provide for maximum
muscle power for 14-16s. (100 m dash) CP ADP
creatine kinase Creatine ATP
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3 Pathways for regenerating ATP during muscle
activity.
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Comparison of energy sources between short term
exercise and prolonged exercise.
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Isotonic and Isometric Exercise

• Isotonic tension increases and the muscle
  shortens
• Lifting weights
• Isometric muscle does not shorten, the tension
  produced never exceeds resistanc
• Trying to pick up a car

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Red (slow) twitch fibers

• Aerobic
• Slow-acting ATPases (enzymes that break down ATP)
  
• Large amounts of myoglobin
• Red color to cell
• Abundant supply of mitochondria
• Fatigue resistant-as long as O2 is available
• High endurance (jogging, swimming, soccer)

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White (fast) twitch fibers

• Large pale cells with twice the diameter of red
  fibers
• Very little myoglobin
• Contain fast-acting ATPases and contract rapidly
• Contain few mitochondria, but large glycogen
  stores
• Depend on anaerobic resp. to make ATP, therefore
  fatigues easily
• Low endurance, much power.sprints

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Pink (intermediate) twitch fibers

• Mixture of red and white fibers
• Aerobic mechanisms and fatigue resistant
• Contain fast-acting ATPases
• High myoglobin content

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Force of Muscle Contraction

• Number of Muscle Fibers Stimulated
• Size of the Muscle Fibers (red vs. white)
• Frequency of Stimulation
• Degree of Muscle Stretch

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Factors influencing force of skeletal muscle
contraction.
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Length-tension relationships of sarcomeres in
skeletal muscles.