Muscles II - Animal Physiology

Zoology 430: Animal Physiology

Muscles II

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Road Map

2

SensoryReceptors

Central NS

MusclesGlands

Peripheral NS

Afferent

EfferentMotor Output

Sensory Input


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

Zoology 430: Animal Physiology 4

Muscle Model

Load

Series Elastic Component (Tendon)

Parallel Elastic Component

(Membranes)Contractile Unit (Sarcomeres)


Isotonic Contraction

Time

Leng

th sh

orte

ned

Forc

e

Stretch SEC


Professor Full’s

Knee

6

Tendon transmits force to skeleton,

smoothes movement and

stores and returns energy.

Repaired


Isometric Contraction

7Time

Forc

e

Stretch SEC

TwitchTetanus


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)


Activation and Summation

9

TimeStimulation (Action potential)

Single

Twitch

Low frequency High frequency

Fused TetanusUnfused

TetanusForc

e

Isometric contraction Maximum isometric force


Activation

10

Muscle Force

Stimulation (EMG)

Human

Cockroach


Force-velocity and power-velocity relationships of muscle contraction

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Power = Force x Velocity of Contraction


Why is force inversely related to velocity?


Muscle Fiber Types

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Are all muscle fibers the same?

Dark meat Red fibers

Light meat White fibers

Fish Human leg(aerobic)

(anaerobic-burst)


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


Twitch fiber characteristics

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Fast vs. Slow Twitch Fibers


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


Adaptation for Power: Jumping Frogs

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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


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.


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


© 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!


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


Heat generated by RM also warms WM and increases contraction speed


Optimized Motors

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Escape response


Motor Unit Recruitment

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Motor Neurons

Motor unit - motor neuron and its innervated muscle fibers

Muscle fibers


Innervation and Control

2824

Excitatory Motor Neuron

Inhibitory Motor Neuron

Polyneuronal Innervation

Multiterminal Innervation

Arthropods

Eckert


Control Strategies

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Vertebrates

Arthropods

Action Potential

Electrotonic Potentials

Graded Contractions

Twitch

Single

MultipleEckert


Predictions

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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


Myasthenia gravis

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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.


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


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


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


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


Toadfish Ca2+ kinetics

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Sailfish

Spearfish

Blue Marlin

Billfishes: Heater organs


Pacific Blue marlin


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


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


Changes in Muscle Function over a lifetime

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Acclimitization (Training)Atrophy Myopathic Diseases


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


Endurance Training:

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• Increases Vascularization

• Increases oxidative capacity


Resistance Training

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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


Ageing Atrophy

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Ageing Atrophy

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• Loss of Muscle Fibers through denervation

• Conversion of Fast Fibers to Slow Fibers


Myopathic Diseases

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• Acquired (Dermatomyositis (prednisone)) • Inherited (Muscular Dystrophy)

– Mutation in Dystrophin-Costamere System

Dystrophin


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.

Muscles II - Animal Physiology

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