Download Muscular System PPT

Essentials of Human Anatomy & Physiology
Chapter 8
The Muscular System
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Function of Muscles
 Produce movement
 Maintain posture / Stabilize joints
 Regulation of body temperature /
Generate heat
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Connective Tissue Wrappings of
Skeletal Muscle
 Epimysium –
covers the
entire skeletal
muscle
Figure 6.1
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Connective Tissue Wrappings of
Skeletal Muscle
 Perimysium –
around a fascicle
(bundle of muscle
fibers)
 Endomysium –
around single
muscle fiber
(individual muscle
cell
Figure 6.1
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Microscopic Anatomy of Skeletal
Muscle
 Myofibril
 Bundles of myofilaments
 Myofibrils give skeletal muscle their striated
appearance
Figure 6.3b
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Microscopic Anatomy of Skeletal
Muscle
 Sarcomere = Contractile unit of a muscle fiber
 Thick filaments = Composed of the protein
myosin
 Thin filaments = Composed of the protein
actin
Figure 6.3c
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Muscle Contraction – Motor Units
 Skeletal
muscles must
be stimulated
by a nerve to
contract (motor
neuron)
 Motor unit
 One neuron
 Muscle fibers
stimulated by
that neuron
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.4a
Muscle Contraction - Synapse
 Neuromuscular
junctions – site of
nerve and muscle
connection
 Neurotransmitters
(Acetylcholine) are
released upon arrival
of a nerve impulse
 Triggers muscle
contraction upon
diffusing across the
synapse
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.5b
The Sliding Filament Theory of
Muscle Contraction
Figure 6.7
The Sliding Filament Theory of
Muscle Contraction
 This continued
action causes a
sliding of the myosin
along the actin
 The result is that the
muscle is shortened
(contracted)
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Figure 6.7
Principles of Muscle Contraction
 Threshold Stimulus
 The minimal strength of a stimulus required to
cause muscle contraction
 All or None Law
 If a threshold stimulus is met a skeletal
muscle fiber will contract to its fullest extent
(or not all).
 Recruitment
 Signifies an increase in motor units activating
due to varying levels of stimulation
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Muscle Response to Stimuli
 Muscle force depends upon the number
of fibers (motor units) stimulated
 More fibers contracting results in
greater muscle tension (Strength)
 Less fibers contracting results in
decreased muscle tension (Strength)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Energy for Muscle Contraction
 Initially, muscles use available Adenosine
Triphosphate (ATP) for energy
 Bonds of ATP are broken to release energy
 Only 4-6 seconds worth of ATP is stored by
muscles
 After this initial time, other pathways must
be utilized to produce ATP
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Energy for Muscle Contraction
• Creatine Phosphate
 Muscle cells contain a high
energy molecule called
creatine phosphate (CP)
 After ATP is depleted, ADP is
left
 CP transfers energy to ADP in
the transfer of a P, to
regenerate ATP
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Figure 6.10a
Energy for Muscle Contraction
 Anaerobic Respiration
 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
 Lactic acid produces
muscle soreness and
cramping
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Figure 6.10b
Energy for Muscle Contraction
 Aerobic Respiration
 Series of metabolic
pathways that occur in
the mitochondria
 Glucose is broken down
to carbon dioxide, water
and ATP
 This is a slower reaction
that requires continuous
oxygen
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.10c
Muscle Fatigue
 Muscular Fatigue – Lack of production of
ATP to sustain muscle contraction
 Synaptic Fatigue – Lack of production of
Acetylcholine to pass across the synapse
 Psychological Fatigue – neuromuscular
system is functional, mind “gives up”.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings