Transcript Physiology of Muscle Part 2

PowerPoint® Lecture Slide Presentation
by Patty Bostwick-Taylor,
Florence-Darlington Technical College
The Muscular
System
6
PART B
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Contraction of Skeletal Muscle
 Muscle fiber contraction is “all or none”
 A muscle fiber will contract fully or not at all
 Muscle fibers do not partially contract
 For a stronger reaction, more motor fibers or
units have to be recruited
 The minimum level needed to cause a muscle
contraction is called the threshold stimulus
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All or None Principal continued
 Within a skeletal muscle, not all fibers may be
stimulated during the same interval
 Different combinations of muscle fiber
contractions may give differing responses
 Graded responses—different degrees of skeletal
muscle shortening
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Contraction of Skeletal Muscle
 Graded responses can be produced by changing
 The frequency of muscle stimulation
 The number of muscle cells being stimulated
at one time
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Graded Strength Principle
 Skeletal muscle organs do not follow the all or none
principle
 1. If many fibers of a muscle organ become fatigued,
the entire muscle will suffer some loss in its ability to
generate maximum force of a contraction
 The more fibers contracting = more strength
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Graded Strength Principle
 2. How many fibers stimulated depends on how
many motor units are recruited.
 The more intense and frequent a stimulus, the
more motor units are recruited and the stronger
the contraction
 After threshold stimulus is achieved, a continued
increase in stimulus strength produces a
proportional increase in muscle strength until the
maximal level of contraction is achieved.
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Graded Strength Principle
 3. The strength a muscle can develop is related to
the length of its fibers
 Too short or too long and it can’t develop tension
 4. The heavier the load, the stronger the contraction.
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Myography
 Muscle graph, used to study muscle contractions
 Threshold stimulus needed to make muscle
contract
 Latent period
 Impulse travels to sarcolemma and ttubules
 SR releases CA
 Ca takes troponin and tropomyosin from
the actin
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Myography
 Contraction Phase
 Myofilaments slide past each other
 Z lines are drawn in
 Relaxation
 Ca goes back to SR
 Crossbridges break
 Troponin and tropomyosin go back
 Z lines go back
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Types of Graded Responses
 Twitch
 Single, brief contraction
 Not a normal muscle function
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Types of Graded Responses
Figure 6.9a
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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
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Types of Graded Responses
Figure 6.9b
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Types of Graded Responses
 Unfused (incomplete) tetanus
 Some relaxation occurs between contractions
 The results are summed
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Types of Graded Responses
Figure 6.9c
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Treppe or Staircase
 Also called treppe or staircase phenomenon
 Shows that a muscle will contract more forcefully
once it has contracted a few times
 This is why athletes warm-up
 Not sure why it happens but think Ca does not go
all the way back to the SR between contractions
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Types of Graded Responses
 Fused (complete) tetanus
 No evidence of relaxation before the following
contractions
 The result is a sustained muscle contraction
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Types of Graded Responses
Figure 6.9d
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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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Physiological Fatigue vs. Psychological Fatigue
 Repeated stimulation lessens a muscle’s
excitability and contractility and results in muscle
fatigue
 In muscle fatigue the muscle does not repond
to the strongest stimuli
 Physiological fatigue is caused by a lack of ATP
 Rarely occurs
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Physiological Fatigue vs. Psychological Fatigue
 Physiological fatigue produces that exhausted
feeling that causes us to stop muscular activity
 In physiological fatigue we can’t contract our
muscles but in psychological fatigue we simply
will not contract our muscles.
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Abnormal muscle contractions
 Convulsions
 Abnormal uncoordinated tetanic contractions
 Fibrillation
 Individual fibers contract asynchronoously
rather than at one time
 Produces a flutter of the muscle, but no
movement
 Common in the heart
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Energy for Muscle Contraction
 Initially, muscles use stored ATP for energy
 ATP bonds 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
 ATP is formed in the mitochondria
 Adensine Triphosphate
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Energy for Muscle Contraction
 Direct phosphorylation of ADP by creatine
phosphate (CP)
 Muscle cells store CP
 CP is a high-energy molecule
 After ATP is depleted, ADP is left
 CP transfers energy to ADP, to regenerate
ATP
 CP supplies are exhausted in less than 15
seconds
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Energy for Muscle Contraction
Figure 6.10a
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Anerobic Glycolysis (Lactic Acid System)
 Glucose is a type of sugar
 If in the blood it is glucose
 If in the liver it is glycogen
 Anerobic means without oxygen
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Anerobic Glycolysis
 Glucose Molecule splits (C6 H12 O6)
 Lactic Acid (C3H6O3)
Lactic Acid
 Lactic Acid loses two Hydrogens and becomes
Pyruvic Acid (C3 H4 O3)
 The hydrogen has to find someplace to go
 If there is enough O2, it will take it to the electron
transport system
 If not enough O2, it will combine with the pyruvic
acid and go back to lactic acid
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Anerobic Glycolysis
 When your body reaches its limit of LA this
energy system shuts down
 Through training you can teach your body to
handle more lactic acid
 This system lasts from 30 seconds to 3 minutes
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Energy for Muscle Contraction
Figure 6.10b
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Energy for Muscle Contraction
 Anaerobic glycolysis and lactic acid formation
 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
 This reaction is not as efficient, but is fast
 Huge amounts of glucose are needed
 Lactic acid produces muscle fatigue
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Energy for Muscle Contraction
Figure 6.10c
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Energy for Muscle Contraction
 Aerobic respiration
 Takes at least 3 minutes to get into
 Used for long term events
 Pyruvic Acid goes through the Kreb’s cycle in
the mitochondria
 End up with 32 ATP
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Anerobic Threshold
 Point of exercise when you switch from aerobic to
anerobic
 Lactic Acid builds up again
 If you exceed this threshold, you don’t get any
training benefits
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Anerobic Threshold
 To run the fastest race possible, you must run
just under your anerobic threshold and at the
proper distance from the finish line, increase your
speed so that the max L.A. accumulation will
occur at the finish line.
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Recovery
 You enter recovery having an oxygen debt
 Oxygen debt is the amount of oxygen needed to
convert lactic acid back to glucose
 This is why you breathe hard after exercise
 also why metabolism stays up after exercise
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Recovery
 To rid the body of Lactic acid you use heat to
increase blood flow to the muscle and get rid of it
faster or do a slow jog which will use oxygen and
help get rid of lactic acid
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Fast and Slow Twitch Muscle Fiber
 Myoglobin is large protein molecule that takes
oxygen to muscles
 If it has a lot of myoglobin it is called red
muscle fibers
 also called slow twitch fibers
 contracts many times before it gets tired
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Fast and Slow Twitch Muscle Fiber
 If it doesn’t have as much myoglobin it
is called white muscle fibers
 fatique more quickly
 Intermediate fibers
 somewhere in between the two
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Tonic Contraction
 Is a continual partial contraction
 A small number of the total number of fibers
contract
 Also called muscle tone
 It is the muscles of normal individuals when they
are awake
 If you go unconscious you can’t sit or stand
 tonic- is more than normal tone
 Flaccid- is less than normal tone
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Types of Muscle Contractions
 Isotonic contractions
 Means same tension
 The muscle shortens and movement occurs
 Isometric contractions
 Means same length
 Tension in the muscles increases
 The muscle is unable to shorten or produce
movement
 Most body movements are a combination of the
two
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Effect of Exercise on Muscles
 Exercise increases muscle size, strength, and
endurance
 Aerobic (endurance) exercise (biking, jogging)
results in stronger, more flexible muscles with
greater resistance to fatigue
 Makes body metabolism more efficient
 Improves digestion, coordination
 Resistance (isometric) exercise (weight lifting)
increases muscle size and strength
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Effect of Exercise on Muscles
 Atrophy is when a muscle shrinks in mass
 Hypertrophy is an increase in muscle size
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Diseases
 myopathies are muscle disorders
 muscle strain involves the
overstretching or tearing of muscle
fibers
 muscle sprain if injury occurs in a
joint and a ligament is damaged
 muscle myositis is muscle
inflammation
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Muscle Infections
 bacteria and viruses can infect
muscles and cause muscle
soreness when you get the flu
 often produce a myelitis which is a
muscle infection
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Poliomyelitis
 is a viral infection of the nerves that
control skeletal movement
 can cause paralysis and death if
affects lungs
 uncommon in U.S. because of
vaccinations, but common in other
countries
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Poliomyelitis
 two types of immunity
 one is a dead virus and can not
cause the disease
 one is a live virus and can cause
the disease
 there is no cure for polio
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Myasthenia Gravis
 muscle weakness in the face and
throat
 immune system attacks muscle
cells at the neuromuscular junction
so muscle can’t be stimulated
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Hernias
 weakness of the abdominal muscle
can lead to the protrusion of an
abdominal organ through the
abdominal wall
 usually an intestine
 is reducible if it can be put back in
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Hernias
 strangulated is when it is not
reducible and blood flow to the
intestines is stopped
 emergency surgery is needed
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Muscular Dystrophy
 characterized by the wasting away
of muscle tissue
 Duchenne’s MD is the most
common and understood
 replaces muscle with fat and
fibrous tissue
 usually affects skeletal muscles,
but facial muscles not affected
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Muscular Dystrophy
 can affect cardiac muscle
 starts about age 3 and usually fatal
by age 21
 occurs mainly in boys and is an xlinked or sex-linked genetic
disorder
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