muscles ii - animal physiology
TRANSCRIPT
Zoology 430: Animal Physiology
Muscles II
1
Zoology 430: Animal Physiology
Road Map
2
SensoryReceptors
Central NS
MusclesGlands
Peripheral NS
Afferent
EfferentMotor Output
Sensory Input
Zoology 430: Animal Physiology
Muscle Contraction Types
3
2. Isometric contraction (Gr. Iso - same, metric - length) - muscle develops force
1. Isotonic contraction (Gr. Iso - same, tonic - tension) - muscle shortens
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Muscle Model
Load
Series Elastic Component (Tendon)
Parallel Elastic Component
(Membranes)Contractile Unit (Sarcomeres)
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Isotonic Contraction
Time
Leng
th sh
orte
ned
Forc
e
Stretch SEC
Zoology 430: Animal Physiology
Professor Full’s
Knee
6
Tendon transmits force to skeleton,
smoothes movement and
stores and returns energy.
Repaired
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Isometric Contraction
7Time
Forc
e
Stretch SEC
TwitchTetanus
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ONE SECOND
200 MSEC(Pearson, 1976)
CAT
COCKROACHFLEXORS
EXTENSORS
FLEXORS
EXTENSORS
GROUND CONTACTPERIOD
COXA
FEMUR
In Vivo ActivationMuscles Activated by a Series of Neural Signals
(Action Potentials or Spikes)
Electromyogram (EMG)
Zoology 430: Animal Physiology
Activation and Summation
9
TimeStimulation (Action potential)
Single
Twitch
Low frequency High frequency
Fused TetanusUnfused
TetanusForc
e
Isometric contraction Maximum isometric force
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Activation
10
Muscle Force
Stimulation (EMG)
Human
Cockroach
Zoology 430: Animal Physiology
Force-velocity and power-velocity relationships of muscle contraction
11
Power = Force x Velocity of Contraction
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Why is force inversely related to velocity?
Zoology 430: Animal Physiology
Muscle Fiber Types
13
Are all muscle fibers the same?
Dark meat Red fibers
Light meat White fibers
Fish Human leg(aerobic)
(anaerobic-burst)
Zoology 430: Animal Physiology
Whole muscles consist of different fiber types
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Twitch: 3 types Fast Glycolytic Fast Oxidative Slow Oxidative Tonic: 1 type Very slow, uncommon
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Twitch fiber characteristics
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Fast vs. Slow Twitch Fibers
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Adaptation of muscle function
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• Velocity of shortening (V/Vmax) • Timing and duration of muscle activity • Muscle size • Fiber types • Arrangement of fiber types • Temperature • Overlap of thick and thin filaments • Muscle attachment
Zoology 430: Animal Physiology
Adaptation for Power: Jumping Frogs
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Zoology 430: Animal Physiology
Adaptation for Power: Jumping Frogs
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• Frogs move rapidly – from crouched to extended position in 50-100 ms
• Power produced = jump height • Frogs jump when sarcomere length and
muscle contraction velocity are optimal
Zoology 430: Animal Physiology
Muscle Fibers Types
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Fish have white muscle fibers (Type IIb) on the inside for rapid, escape swimming.
Slow (white) fibers have helical arrangement -- connecting myomeres for rapid burst
Fish have red muscle fibers (Type I) on the outside for slow, continuous swimming.
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Biewener (2003) Animal Locomotion
Fish Red and White Muscle Fiber Arrangement
Slow-twitch (red) fibers are oxidative (aerobic), have rich blood supply, contract slowly, but do not fatigue or go into oxygen debt.
Fast-twitch (white) fibers are glycolytic (anerobic), optimized for fast bursts of speed.
Tunas keep their slow-twitch muscles warm by having them arranged internally to fast-twitch muscles.
Mackerel: a typical telost fish.
Tuna: a cruiser.
red red
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© 2005 Nature Publishing Group
Mammal-like muscles power swimming in acold-water sharkDiego Bernal1,2, Jeanine M. Donley3, Robert E. Shadwick2† & Douglas A. Syme4
Effects of temperature onmuscle contraction and powering move-ment are profound, outwardly obvious, and of great consequenceto survival1,2. To cope with the effects of environmental tempera-ture fluctuations, endothermic birds and mammals maintain arelatively warm and constant body temperature, whereas mostfishes and other vertebrates are ectothermic and conform to theirthermal niche, compromising performance at colder tempera-tures2,3. However, within the fishes the tunas and lamnid sharksdeviate from the ectothermic strategy, maintaining elevatedcore body temperatures4,5 that presumably confer physiologicaladvantages for their roles as fast and continuously swimmingpelagic predators. Here we show that the salmon shark, a lamnidinhabiting cold, north Pacific waters, has become so specializedfor endothermy that its red, aerobic, locomotor muscles, whichpower continuous swimming, seem mammal-like, functioningonly within a markedly elevated temperature range (20–30 8C).These muscles are ineffectual if exposed to the cool water tem-peratures, and when warmed even 10 8C above ambient they stillproduce only 25–50% of the power produced at 26 8C. In contrast,the white muscles, powering burst swimming, do not show such amarked thermal dependence and work well across a wide range oftemperatures.An anatomical feature that sets the lamnid sharks apart from
ectothermic fishes but reveals evolutionary convergence with tunas isthe location of the red, aerobic, locomotor muscle (RM), being deepin the body next to the vertebral column and concentrated in themid-body region, in contrast with the lateral and subcutaneousposition of RM in other fishes6. Coupled with vascular heatexchangers, tunas and lamnid sharks have evolved the ability toretain metabolic heat in RM and attain temperatures that aresignificantly above that of the surrounding water5,6. Furthermore,the white locomotor muscle (WM) is also significantly warmed byconductive heat transfer arising from its proximity to the RM, withprogressive cooling towards the skin7. Thus, two of the most strikingdifferences between endothermic and ectothermic fishes are theposition of the RM and the capacity to warm both the RM and aportion of the WM.What are the functional consequences of these thermal and
anatomical modifications? Previous work on the swimming physi-ology and metabolic biochemistry of muscles in warm-bodiedlamnid sharks7,8 and tunas9,10 suggests that these fishes have thepotential to sustain a higher aerobic swimming metabolism, andhave an increased potential for burst swimming relative to that ofother fishes. However, there is no direct experimental evidencedemonstrating how a change in the operating temperature of thesetissues might affect the contractile properties of shark muscle, ifthe maintenance of high temperatures in RM is necessary for
satisfactory function, or if warm-bodied sharks are capable ofenhanced swimming performance11. To address these questions weexamined thermal effects on the contractile properties of RM andWM in salmon sharks (Lamna ditropis), a species inhabiting the coldwaters of the north Pacific Ocean12 but noted for maintainingelevated body temperatures6,13,14 and prized as a sport-fish for itsimpressive swimming power and speed15.Within minutes of landing the sharks we mapped the thermal
gradient in the muscle mass by measuring temperatures along thebody. Measurements taken just anterior to the first dorsal fin, wherethe RM is most abundant, showed that all sharks had a coretemperature about 18–20 8C above the surrounding sea surfacetemperature, which ranged from 6 8C to 8 8C; this gradient is evenlarger than those reported previously6,13,14, probably due to thesomewhat cooler surface temperature at the time of this study.Regardless of variations in surface temperatures, tagging studieshave shown that salmon sharks routinely dive to 200m and encoun-ter water temperatures of 6 8C during most of the year12. Themaximum temperature of the deeply positioned RM was 26 8C,which was 16 8C warmer than the superficial WM at this positionand about 20 8C warmer than the ambient water. A smaller thermalgradient was present at the level of the second dorsal fin, a narrowerregion of the body, with the deep RM temperature being 10–13 8Cabove ambient. In Fig. 1, the thermal data from all specimens areshown superimposed on a three-dimensional reconstruction of thedistribution of locomotor muscle in the salmon shark, providing aperspective of the operating temperatures in situ for the RM andWM along both the longitudinal and transverse axes of the body.Temperatures selected from this reconstruction were used todetermine thermal effects on muscle contractile properties.Using a portable stimulator/transducer to make measurements of
muscle twitches in situ, we next determined that the duration oftwitches from superficial WM was invariant along the length of thebody (see Supplementary Fig. 1) but decreased significantly (that is,the twitches got faster) with depth along the temperature gradient ofWM from the cool skin to the warm body core. Contractile tests werethen conducted on small bundles of livingmuscle fibres isolated fromamidbody position (that is, at the level just anterior to the first dorsalfin), where the RM and WM temperatures were the most elevated.Durations of isometric twitches measured from WM ranged from143ms at 10 8C to 51ms at 26 8C, yielding an average thermal ratecoefficient (Q10) of 2.0 (Fig. 2), a typical temperature response formuscle from an ectothermic vertebrate1. In contrast to WM, thetwitch times of RM had both much higherQ10 values (up to 3.7) andexceedingly long twitch durations, with a time to reach peak forceexceeding 3 s at 10 8C, and even longer relaxation times (see Fig. 2).These observations indicate that the RM is extremely sensitive
LETTERS
1Department of Biology, University of Massachusetts, Dartmouth, North Dartmouth, Massachusetts 02747, USA. 2Marine Biology Research Division, Scripps Institution ofOceanography, La Jolla, California 92093-0202, USA. 3Department of Biological Sciences, Miracosta College, Oceanside, California 92056, USA. 4Department of BiologicalSciences, University of Calgary, Alberta, T2N 1N4 Canada. †Present address: Department of Zoology, University of British Columbia, Vancouver, British Columbia, V6T 1Z4,Canada.
Vol 437|27 October 2005|doi:10.1038/nature04007
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These lamnid sharks live in very cold waterUsed temperature probes to measure muscle T immediatelyCore (Red Muscle) is up at 26C! 16-20C higher than ambient!
Zoology 430: Animal Physiology
Muscle twitch duration at different temperatures
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Red Muscle
White Muscle
Tuna RM
Used portable stimulator to make measurements in situ
WM twitch duration does not change with Temperature
RM is extremely sensitive to Temp, probably incapable of contracting sufficiently even at 15C
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Heat generated by RM also warms WM and increases contraction speed
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Optimized Motors
26
Escape response
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Motor Unit Recruitment
2723
Motor Neurons
Motor unit - motor neuron and its innervated muscle fibers
Muscle fibers
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Innervation and Control
2824
Excitatory Motor Neuron
Inhibitory Motor Neuron
Polyneuronal Innervation
Multiterminal Innervation
Arthropods
Eckert
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Control Strategies
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Vertebrates
Arthropods
Action Potential
Electrotonic Potentials
Graded Contractions
Twitch
Single
MultipleEckert
Zoology 430: Animal Physiology
Predictions
30
What would happen if the immunological system attacked the receptors of the muscle membrane?1. Reduction in the size of EPSPs.2. Decreased probability of generating an action potential in muscle fiber.3. Not all muscle fibers in a motor unit will be activated.4. Muscle weakness.
Myasthenia gravis
Zoology 430: Animal Physiology
Myasthenia gravis
31
The hallmark of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest.
Certain muscles such as those that control eye and eyelid movement, facial expression, chewing, talking, and swallowing are often, but not always, involved in the disorder.
The muscles that control breathing and neck and limb movements may also be affected.
Zoology 430: Animal Physiology
Muscle adaptation for non-locomotory function
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• Electrical potential generation – Electric Eels
• Sound production – Rattlesnake rattle, Toadfish swimbladder
• Heat generation – Ocular muscles in billfishes
Tradeoffs: Increased density of energy production, decreaseddensity of contractile apparatus
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Electrical Organs
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• Modified muscles (electrocytes) lack contractile apparatus – 1000s of electrocytes in series
• Simultaneous excitation of all electrocytes produces large electrical discharge – 650 V
Zoology 430: Animal Physiology
Sound Production: Rattlesnakes
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• Rattlesnake “rattler” can have sustained vibrations of over 90 per second (90Hz) for hours
• Rattler shaker muscles have reduced contractile apparati (low force required) and higher energetic components
Zoology 430: Animal Physiology
Sound Production: Toadfish
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• Toadfish makes a mating call 10-12 times per minute for hours on end
• Sound is produced by rapid oscillation of muscles surrounding the fishes swim bladder (100-200 Hz)
• However, toadfish locomotory muscle is very slow (1-2 Hz)
• Difference: Ca2+ kinetics, muscle morphology – Incr. Ca2+ channels – Incr. troponin – Decr. Diffusion distances
Zoology 430: Animal Physiology
Toadfish Ca2+ kinetics
36
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Sailfish
Spearfish
Blue Marlin
Billfishes: Heater organs
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Pacific Blue marlin
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Dep
th, m
0
300
600
Time of day
sunset sunrise
T/D record from a swordfish
10
Tem
pera
ture
(°C
)25
Eye temp
Water temp
Zoology 430: Animal Physiology
Ocular/Brain Heater Organ
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• Modified Muscle – No contractile apparatus – High mitochondrial volume (65%) and oxidative capacity
• Insect flight muscle: 44% • trout oxidative muscle: 31%
– High sarcoplasmic reticulum (SR) volume • ~30% vs ~ 4% in red muscle
– SR membrane has hyper elevated Ca2+ ATPase – RyR continuously open:
• Continuous THERMOGENIC Ca2+ cycling
• High Mitochondrial Density – High ATP production to support Ca2+ pump
• Some Mitochondria Uncoupled - Heat Production – H+ pumping and H+ATPase disconnected
Zoology 430: Animal Physiology
Changes in Muscle Function over a lifetime
41
Acclimitization (Training)Atrophy Myopathic Diseases
Zoology 430: Animal Physiology
Acclimation/Acclimatization
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• Changes in muscle within an organisms lifetime: – Training – Atrophy
• Types of training: – Endurance
• oxidative – Resistance
• anaerobic
Muscles don’t change length or increase number of fibers
Zoology 430: Animal Physiology
Endurance Training:
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• Increases Vascularization
• Increases oxidative capacity
Zoology 430: Animal Physiology
Resistance Training
44
Slow oxidativeFast oxidative
Fast glycolytic
• Increases Muscle Volume – # myofibrils per muscle cell
(myofibril bundles increase within muscle fiber cell -- # muscle fibers don’t change)
• Changes Fiber Composition
Zoology 430: Animal Physiology
Ageing Atrophy
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Zoology 430: Animal Physiology
Ageing Atrophy
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• Loss of Muscle Fibers through denervation
• Conversion of Fast Fibers to Slow Fibers
Zoology 430: Animal Physiology
Myopathic Diseases
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• Acquired (Dermatomyositis (prednisone)) • Inherited (Muscular Dystrophy)
– Mutation in Dystrophin-Costamere System
Dystrophin
Zoology 430: Animal Physiology
Muscular Dystrophies
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• Duchenne is the most severe form of muscular dystrophy – Wheelchair use
• from ~ nine years of age – Restriction of joint motion
• The ankles are usually affected first, and the hips and knees last – Scoliosis
• for example, a sideways curvature of the spine. – Difficulty breathing
• weakness of intercostal muscles - mechanically assisted breathing – Heart problems
• in a small number of cases, there is carciac dystrophy – Early death
• most affected people survive into their 20s. Few survive more than 30 years. • Becker muscular dystrophy is less severe
– People with Becker muscular dystrophy can still walk at 16 years. – Some affected people have lived to over 80 – Scoliosis seldom occurs – The effect on lung function is less severe – Heart trouble is less frequent, although it is occasionally serious.