Sensory Neurons and Muscles

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Chapter 49

• Sensory Neurons and Muscles

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Types of Sensory Neurons

• Mechanoreceptors- detect physical deformations
  pressure, touch, stretch, motion, and sound.
• Stretch receptors-flexion or extension or muscles
• Hair Cells-movement of fluids
• Pain Receptors-pressure
• Chemoreceptors-detect chemical changes in the
  body
• Thermoreceptors-detect temperature changes

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Types of Sensory Neurons Stretch Receptors and
Hair Cells
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Sensory Neurons of the Skin
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Means of animal movement

• Cilia
• Flagellae
• Muscles

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Vertebrate Muscle Types

• Skeletal muscle
• Striated
• Voluntary
• Smooth muscle
• Non-striated
• Involuntary
• Cardiac muscle
• Striated
• Involuntary
• Electrically coupled cells

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Skeletal Muscle

• Many animals contain over 400 skeletal muscles
• 40-50 of total body weight
• Functions of skeletal muscle
• Locomotion and breathing
• Postural support
• Heat production

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Structure of Skeletal MuscleConnective Tissue
Covering

• Epimysium
• Surrounds entire muscle
• Perimysium
• Surrounds bundles of muscle fibers (Fascicles)
• Endomysium
• Surrounds individual muscle fibers

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Structure of Skeletal Muscle Microstructure

• Sarcolemma
• Muscle cell membrane
• Myofibrils
• Threadlike strands within muscle fibers
• Actin (thin filament)
• Troponin
• Tropomyosin
• Myosin (thick filament)

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Structure of Skeletal MuscleMicrostructure

• A band
• Anisotropic (dark)
• I band
• Isotropic (light)
• Z disc
• Zwischenscheibe (between zone)
• a-actinin
• H zone
• Hellerscheibe (clear disc)

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Structure of Skeletal Muscle The Sarcomere
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Muscular Contraction

• The sliding filament model
• Movement of actin filament over the myosin
  filament
• Formation of cross-bridges between actin and
  myosin filaments
• Reduction in the distance between Z-lines of the
  sarcomere

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The sliding-filament model of muscle contraction
0.5 ?m
(a) Relaxed muscle fiber. In a relaxed muscle
fiber, the I bandsand H zone are relatively wide.
Z
H
I
A
Sarcomere
(b) Contracting muscle fiber. During contraction,
the thick andthin filaments slide past each
other, reducing the width of theI bands and H
zone and shortening the sarcomere.
(c) Fully contracted muscle fiber. In a fully
contracted musclefiber, the sarcomere is shorter
still. The thin filaments overlap,eliminating
the H zone. The I bands disappear as the ends
ofthe thick filaments contact the Z lines.
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Cross bridges
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Myosin-actin interactions underlying muscle fiber
contraction
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Hypothetical mechanism for the regulation of
muscle contraction
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Sarcoplasmic Reticulum
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The Neuromuscular Junction

• Site where motor neuron meets the muscle fiber
• Separated by gap called the neuromuscular cleft
• Motor end plate
• Pocket formed around motor neuron by sarcolemma
• Acetylcholine is released from the motor neuron
• Causes an end-plate potential (EPP)
• Depolarization of muscle fiber

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Review of contraction in a skeletal muscle fiber
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Motor units in a vertebrate muscle
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Temporal summation of muscle cell contractions
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Types of Skeletal Muscle Fibers
Type I Type IIa Type IIb
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Fiber Types and athletic performance

• Type I- Slow
• Type II-Fast

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Fiber Types and athletic performance

• Power athletes
• Sprinters
• Possess high percentage of fast fibers (Type IIA
  and IIB)
• Endurance athletes
• Distance runners
• Have high percentage of slow fibers (Type I)
• Others
• Weight lifters and nonathletes
• Have about 50 slow and 50 fast fibers

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Bones and joints of the human skeleton
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Energy-efficient locomotion on land
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The interaction of muscles and skeletons in
movement
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Vertebrate Muscle Types

• Skeletal muscle
• Striated
• Voluntary
• Smooth muscle
• Non-striated
• Involuntary
• Cardiac muscle
• Striated
• Involuntary
• Electrically coupled cells

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Vertebrate Muscle Types

• Skeletal muscle
• Striated
• Voluntary
• Smooth muscle
• Non-striated
• Involuntary
• Cardiac muscle
• Striated
• Involuntary
• Electrically coupled cells

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The mammalian cardiovascular system an overview
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The mammalian heart a closer look
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The cardiac cycle
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The control of heart rhythm
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• Cells are coupled via gap junctions
• Allows electrical event to spread from cell to
  cell

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