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Chpt. 49Chpt. 49Muscles &
Motor Locomotion
Why Do We Why Do We Need All Need All
That ATP?That ATP?
Function of Muscles:• To convert chemical energy of
ATP into mechanical work,• To get around… • To get your food• To digest your food• To pump your heart
so that oxygen canget to that
mitochondria
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• 1) Cardiacrapid contraction
• 2) Skeletalrapid contraction
• 3) Smoothslow sustained contraction
Types of Muscle Tissue:
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voluntary, striated
involuntary, striated
auto-rhythmic
involuntary,
non-striated
evolved first
multi-nucleated
digestive systemarteries, veins
heartmoves bone
As a side …
• Insect flight muscles contract more rapidly than ANY OTHER
• 1,000 contractions/second
• Highest metabolic rate
• Contain more mitochondria than any other tissue
• HOW get oxygen???
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HOW DO WE MOVE THESE 206 BONES?
SKELETAL MUSCLE
skeletal muscles move bones by pulling…not pushing, therefore they come in antagonistic pairs:
So in other words, in order to flex, you must contract your flexor muscles… and in order to, relax, you must contract the
antagonistic muscle
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flexorflexor vs. extensorextensor
Extensor
(quadracep)
Notice the TENDON connects the muscle to the bone.
One bone is pulled towards another bone upon contraction.
Vertebrate Skeletal Muscle
Structure:
tendon
skeletal muscle
muscle fiber (cell)
myofilamentsmyofibrils
plasma membrane
nuclei
composed of smaller & smaller & smaller units
Vertebrate Skeletal Muscle
each muscle fiber = one long, cylindrical, multinucleated cell
Vertebrate Skeletal Muscle
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Muscle fiber cells composed of: bundles of myofibrils (threadlike
structures)
Bundle of fibers
Myofibrils are basically parallel “contractile units”
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Myofibrils consist of even smaller structures:
thick filaments
thin filaments
myofibrils have a regular arrangement
regular arrangement
regular arrangement
regular arrangement
regular arrangement
sarcomere = basic unit of a myofibril - hundreds are connected end to end & make up the myofibril
sarcomeres are made of these proteins:
thick filaments
thin filaments
Thin filaments: actin•Complex (bunch) of proteins:
–braid of actin molecules & tropomyosin fibers•tropomyosin fibers secured with troponin complex•these are proteins
Thick filaments: myosin•Single protein
–myosin molecule•long protein with globular head
bundle of myosin proteins:globular heads aligned
Thick & thin filaments• MyosinMyosin tails aligned together & heads
pointed away from center of sarcomere
sarcomere = basic unit of a myofibril - hundreds are connected end to end & make up the myofibril
SARCOMERESARCOMERE
making up the sarcomere…
Z-lines = the borders
of the sarcomere (actin)
at rest, the thick myosin &
thin actin filaments in the sarcomere do not overlap completely:
area inwhich only thick myosin filaments = H zone
Area inwhich only
thin actin filaments =
I band
Area in which
both: thin actin filaments & thick myosin
filaments = A band
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More muscle anatomy: SARCOLEMMA = plasma membrane
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More muscle anatomy: T tubule = inward extension of the plasma membrane
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More muscle anatomy: mitochondrion = ohh, there are plenty!
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More muscle anatomy: sarcoplasmic reticulum = another name for endoplasmic reticulum
How does the Muscle Contract?
Sliding Filament Model
Motor Unit
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(Usually hundreds of muscle fibers)
NEUROMUSCULAR JUNCTION
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NEUROTRANSMITTOR ~ ACETYLCHOLINE released as action potential moves to synaptic terminal
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of muscle fiber
The acetylcholine causes the action potential to continue in the muscle
fiber
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The action potential spreads into T-Tubules (invaginations in the membrane of the muscle fibers)
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The a.p. opens Ca+2 channels in the
sarcoplasmic reticulum (e.r.)
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The special type of smooth endoplasmic reticulum found in smooth and striated muscle fibers whose function is to store and release calcium ions.
Ca+2 flows & binds to a protein in the actin
filament
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Sliding Sliding Filament Filament ModelModel
At rest myosin binding sites are blocked (with trypomyosin)
Thin actin filament has myosin binding sites…
Sliding Sliding Filament Filament ModelModel
Thin actin filament has myosin binding sites…
myosin binding sites are opened when Ca+2 binds to the troponin.
(Ca+2 is released as a result of acetylcholein rushing through the T-tubules)
Sliding Filament Model
At rest, myosin head is bound to an ATP --
ATP
Sliding Filament Model
when Ca+2 floods into the cell, Myosin head hydrolyzes (breaks) ATP to ADP and P --.
Sliding Filament Model
Myosin binds to Actin --
this forms a cross-bridge
When this occurs, the myosin head changes shape and releases the ADP + P
Sliding Filament Model
the myosin head changes shape and releases the ADP + P
Sliding Filament Model
The thin actin filament is pulled toward the center of the sarcomere…
Sliding Filament Model
Sliding Filament Model
cross-bridge broken when ATP binds back to the myosin head
ATP
3
2
Cleaving ATP ADP + P allows myosin head to bind to actin filament
ATP
formcrossbridge
ADP
releasecrossbridge
shortensarcomere
1
4
ADP expelled
What is the Stimulus that causes muscle to
contract?
Synapse with Neuron & MuscleSynaptic Terminal
of neuron releases acetylcholine
Synapse with Neuron & Muscle
Ca++ released
Binding sites on actin are now exposed.
Myosin head now binds to the actin
Synapse with Neuron & Muscle
ATP
Muscles do not relax until the Ca+
+ is pumped back into the sarcoplasmic reticulum
Put it all together…1
ATP
2
3
4
5
7
6
ATP
Action potential travels
a.p, travels through T-Tubules
Ca+2 released & binds to troponin complex
Cross bridge formed
Ca+2 depleates; cross bridge broken/ ATP back on myosin head
Ca+2 pumped back into s.r. / ATP required
Acetylcholine released
Put it all together…1
ATP
2
3
4
5
7
6
ATP
Muscle limits:
• Muscle fatigue– lack of sugar
• lack of ATP to restore Ca2+
gradient
– low O2
• lactic acidcauses pH drop which interferes with protein function
– synaptic fatigue• loss of acetylcholine
• Muscle cramps– build up of lactic acid – ATP depletion– ion imbalance
• massage or stretching increases circulation
Rigor mortisRigor mortis• So why are dead people “stiffs”?
– no life, no breathing– no breathing, no O2
– no O2, no aerobic respiration– no aerobic respiration, no ATP– no ATP, no Ca2+ pumps– Ca2+ stays in muscle cytoplasm– muscle fibers continually contract• tetany or rigor mortis
– eventually tissues breakdown& relax• measurement for time of death
Money for BeautyMoney for Beauty• What is Botox?–Toxin derived from Closteridium botulinum
–blocks the release of acetylcholine
–Muscles relax… whichtakes away the
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*The transmission of an impulse from a nerve to the surface of a resting muscle initiates a contraction in that muscle. Biochemical and biophysical studies of muscle tissue have resulted in an explanation for muscle contraction known as the sliding-filament theory.
a. Describe the chemical changes that occur when a nerve impulse is transmitted to the surface of a resting muscle cell.
b. Describe the internal structure of a muscle fiber as revealed by electron microscopy.
c. On the basis of this structure, explain the sliding-filament theory.
*7. Discuss the mechanism by which a muscle cell contracts or a nerve cell transmits an impulse. Include in your discussion the relationship between cell structure and function.
• Action potential causes Ca2+ release from SR– Ca2+ binds to troponin
• Troponin moves tropomyosin uncovering myosin binding site on actin
• Myosin binds actin– uses ATP to "ratchet" each time– releases, "unratchets" & binds to next actin
• Myosin pulls actin chain along• Sarcomere shortens
– Z discs move closer together
• Whole fiber shortens contraction!• Ca2+ pumps restore Ca2+ to SR relaxation!– pumps use ATP
ATP
ATP