Download 953040Ch_6.2_Muscle_Contractions

Essentials of Human Anatomy & Physiology
Seventh Edition
Elaine N. Marieb
Chapter 6
The Muscular System
Slides 6.18 – 6.31
Lecture Slides in PowerPoint by Jerry L. Cook
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Functions of Muscles
1. Produce movement – internal & external
2. Maintain posture – lots of little muscles
3. Stabilize joints – done by tendons
4. Generate heat
 75% of energy released in cells is wasted as
heat energy which helps maintain our normal
body temperature
 Skeletal muscle = 40% of body mass, so it
generates a lot of our body heat
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.8
Skeletal Muscle Activity
 Skeletal muscles must be stimulated by
a nerve to contract
 2 properties of skeletal muscle allow us
to move:
Irritability – ability to receive and
respond to a stimulus
Contractility – ability to shorten when
an adequate stimulus is received
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.13
Nerve Stimulus to Muscles
 One nerve or
neuron may
stimulate one
muscle fiber or
hundreds
 Motor unit
 One neuron
 Muscle cells
stimulated by
that neuron
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.4a
Slide 6.14
Neuromuscular Junctions
 Synaptic cleft –
gap between
nerve and
muscle
 Nerve and
muscle do not
make contact
 Area between
nerve and muscle
is filled with
interstitial fluid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.5b
Slide 6.15b
Transmission of Nerve Impulse to Muscle
 Neurotransmitter – chemical released
by nerve upon arrival of nerve impulse
(acetylcholine for skeletal muscle)
 Neurotransmitter attaches to receptors
on the skeletal muscle which becomes
permeable to sodium (Na+)
 This causes an electrical signal to be
sent across the fiber(s), called action
potential, which causes a contraction
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.16a
Contraction of a Skeletal Muscle
 Muscle fiber contraction is “all or none”
 Within a skeletal muscle, not all fibers
may be stimulated during the same
interval
 Different combinations of muscle fiber
contractions may give differing
responses – a gentle stroke or a slap
 Graded responses – different degrees
of skeletal muscle shortening
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.19
Types of Graded Responses
 Twitch
 Single, brief contraction
 Not a normal muscle function
Figure 6.9a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.20a
Types of Graded Responses
 Tetanus (summing of contractions)
 One contraction is immediately followed by
another
 The muscle does
not completely
return to a
resting state
 The effects
are added
 May be complete
or incomplete
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.20b
Types of Tetanus
 Unfused (Incomplete) Tetanus
 Some relaxation occurs between
contractions; results are summed
 Fused (complete) Tetanus
 No relaxation between contractions; result
is a sustained contraction
Muscle Response to Strong Stimuli
 Complete tetanus produces stronger
contractions but mostly it produces a
longer, sustained contraction
 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.22
Energy for Muscle Contraction
 Initially, muscles used stored ATP for
energy
 Bonds of ATP are broken to release energy
 Only 4-6 seconds worth of contractions is in
the ATP stored by muscles
 After this initial time, the muscle must
regenerate its ATP (change ADP back to
ATP)
 3 options available
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.23
Regeneration of ATP
 3 options available:
Direct phosphorylation of ADP by
creatin phospate
Aerobic respiration
Anaerobic respiration (glycolysis)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.23
Direct Phosphorylation by CP
 After ATP is depleted, ADP is
left
 Muscle cells contain creatine
phosphate (CP)which contains
a high-energy phosphate group
 CP transfers its phosphate to
ADP, to regenerate ATP
 Happens in a fraction of a
second
 CP supplies are exhausted in
about 20 seconds
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.10a
Slide 6.24
Aerobic Respiration
 Series of metabolic pathways
that occur in the mitochondria
 Glucose is broken down to
carbon dioxide and water,
releasing energy
 36 ATP are produced per
molecule of glucose
 This is a slower reaction that
requires continuous oxygen
 95% of our energy during rest
or light exercise is produced
this way
Figure 6.10c
Slide 6.25
Anaerobic Glycolysis (Respiration)
 Reaction that breaks down
glucose without oxygen
 Aerobic respiration starts
without oxygen - produces 2
ATP and pyruvic acid; then
oxygen + pyruvic acid
produce other 34 ATP
 Anaerobic starts the same
way: 2 ATP from glucose
 But is only 5% as efficient
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.10b
Slide 6.26a
Anaerobic Glycolysis
 Pyruvic acid is
converted to lactic acid
 Lactic acid can produce
ATP w/o oxygen
 Reaction is 2.5X faster
and can continue for 3060 seconds
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.10b
Slide 6.26b
Anaerobic Glycolysis
 Gets muscles through
strenuous or demanding
times when oxygen can’t get
to muscle fast enough
 Drawbacks are that it
consumes huge amounts for
glucose for a small amount of
ATP
 Also it leaves muscles
fatigued – tired and sore from
the lactic acid
Figure 6.10b
Slide 6.26b
Muscle Fatigue and Oxygen Debt
 When a muscle is fatigued, it is unable to
contract even when being stimulated
 Increasing acidity (from lactic acid) and lack
of ATP causes the muscle to contract less
 The common reason for muscle fatigue is
oxygen debt (caused by anaerobic glycolysis)
 Oxygen must be “repaid” to tissue to remove
oxygen debt
 Oxygen is required to get rid of accumulated
lactic acid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.27
Types of Muscle Contractions
 Isotonic contractions
 The muscle shortens
 Movement occurs
 Most muscle contractions
 Isometric contractions
 Tension in the muscles increases, but the
muscle is unable to shorten
 No movement occurs
 Example: trying to lift a car
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.28
Muscle Tone
 Some fibers are contracted even in a
relaxed muscle
 Different fibers contract at different
times to provide muscle tone
 The process of stimulating various
fibers is under involuntary control
 Keeps our muscles firm, healthy &
ready for action
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.29
Muscle Tone
 If the nerve is destroyed in an accident,
the muscle can not stay toned.
 Muscle becomes flaccid and begins to
atrophy.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.29
Endurance/Increased Muscle Strength
 To increase endurance, aerobic
exercise is the most efficient
 Aerobic exercise increases the number
of mitochondria, blood flow and oxygen
flow to muscles
 Also improves the functioning of almost
every other body system
 To increase muscle size, requires
resistance training which increases the
size of muscle fibers
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.29
Effects of Exercise on Muscle
 Results of increased muscle use
 Increase in muscle size
 Increase in muscle strength
 Increase in muscle efficiency
 Muscle becomes more fatigue resistant
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.31