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SKELETAL MUSCLE SKELETAL MUSCLE CONTRACTIONCONTRACTION

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Muscle CharacteristicsMuscle Characteristics

• 4 major functional characteristics– Contractility

• Capacity of muscle to contract forcefully

– Excitability• Responds to stimulation by nerves or hormones

– Extensibility• Muscles can be stretched to normal resting length

and beyond to a limited degree

– Elasticity• If muscles are stretched, they can recoil to their

original resting length

muscles move the muscles move the bodybody

through skeletal muscle contraction that produce muscle tension

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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Muscle structureMuscle structure














http://home.earthlink.net/~dayvdanls/biology1_2/physiolect8.htm








Longitudinal Section of Longitudinal Section of MyofibrilMyofibril

I


SarcomereSarcomere


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molecular basis of molecular basis of muscle contraction:muscle contraction:repeated sliding of myofilaments

at sufficient ATP and Ca

Neuromuscular JunctionNeuromuscular Junction

LECTURE 18

NMJ and Motor End PlateNMJ and Motor End Plate

AP

Synaptic Cleft

Motor End Plate

Na+

AP

Synapse

Excitation of the Muscle

Ca++ Voltage-gatedChannels

LECTURE 18

Skeletal Muscle Skeletal Muscle InnervationInnervation

Figure 10.10cAndrei R. Manolescu M.D. Department of Physiology, Faculty of Medicine University of Alberta - Sept 27 2005













The Contraction CycleThe Contraction Cycle

Figure 10.12Andrei R. Manolescu M.D. Department of Physiology, Faculty of Medicine University of Alberta - Sept 27 2005


Figure 10.12

Andrei R. Manolescu M.D. Department of Physiology, Faculty of Medicine University of Alberta - Sept 27 2005


Figure 10.12

Andrei R. Manolescu M.D. Department of Physiology, Faculty of Medicine University of Alberta - Sept 27 2005

Based in part onColor Atlas of Physiology, Agamemnon Despopoulos, Stefan SilbernaglThieme Medical Publishers, Inc. , 1991, New York

http://www.sci.sdsu.edu/movies/actin_myosin.html

Actin Myosin Crossbridge 3D Actin Myosin Crossbridge 3D AnimationAnimation

San Diego State University College of SciencesSan Diego State University College of Sciences

Andrei R. Manolescu M.D. Department of Physiology, Faculty of Medicine University of Alberta Sept 27th , 2005

Changes in the appearance of a Changes in the appearance of a Sarcomere during the Contraction of a Sarcomere during the Contraction of a

Skeletal Muscle FiberSkeletal Muscle Fiber

muscle contraction muscle contraction produces tensionproduces tension

Isotonic Contractions

Figure 9.17 (a)

Elaine N. Marieb Human Anatomy & Physiology, Sixth Edition

Isometric Contractions

Figure 9.17 (b)Elaine N. Marieb Human Anatomy & Physiology, Sixth Edition



Silverthorn; Human Physiology An Integrated approach

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Metabolism for Metabolism for muscle contractionmuscle contraction

Muscle Metabolism: Energy Muscle Metabolism: Energy for Contractionfor Contraction

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.18


Energy for ContractionEnergy for ContractionEnergy for ContractionEnergy for Contraction

Vander, Sherman, Luciano's Human Physiology: The Mechanisms of Body Function, 9/e

Nelson, D. L., and M. M. Cox. 2000. Lehninger principles of biochemistry, 3rd ed., p. 604. Worth Publishers, New York.

Metabolic PathwaysMetabolic Pathways

Copyright 2001-2004, E.C. Niederhoffer. All Rights Reserved.




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Kind of exerciseKind of exercise

for weight control?

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Kind of exerciseKind of exercise

for building muscle?

Molecular Model of Sarcomere

(http://cellbio.annualreviews.org/cgi/content/full/18/1/637)Molecular model of the I-band, A-band, and M-line regions of the sarcomere. Polar thin filaments, containing actin, tropomyosin, troponins C, I, and T, and single molecules of skeletal muscle nebulin, span the I-band and interdigitate with the myosin (thick) filaments in the A-band, where they are capped at their pointed ends by tropomodulin. The myosin heads extend from the core of the thick filaments in the C-zone of the A-band, and are anchored and aligned in the middle of the sarcomere, the M-line. Myosin-binding proteins, including MyBP-C, are associated with the thick filaments and likely play multiple roles in the sarcomere. Single molecules of the giant protein titin extend an entire half sarcomere and are proposed to function as a template for sarcomere assembly. Titin's I-band region contains elastic elements that contribute to the passive force of myofibrils. The M-line proteins myomesin and M-protein, as well as MyBP-C, likely contribute to the linkage of thick filaments with titin, whereas MURF-1 and p94 may function in titin M-line region protein turn-over. Also shown here is Novex-3, a novel mini-titin, that binds to another giant protein, obscurin. Other novel titin isoforms have been found that are not shown here. Components whose binding sites are unknown are shown with question marks.


Molecular Model of Sarcomere

(http://cellbio.annualreviews.org/cgi/content/full/18/1/637)Molecular model of sarcomeric Z-disk components, which form the borders of individual sarcomeres. Opposing thin filaments and individual titin molecules interdigitate at the Z-line and are cross-linked by {alpha}-actinin dimers. The diagram depicts one {alpha}-actinin dimer simultaneously cross-linking two actin filaments and two titin molecules; other configurations are possible. Myopodin and filamin can also bind actin filaments, but it is not clear if they actually cross-link opposing thin filaments, as indicated here. Z-line-associated proteins are shown individually or with known binding partners; the two-dimensional nature of the drawing prevents a full appreciation of how the proteins are arranged with respect to each other. Proteins whose binding sites are unknown are indicated with question marks. It is possible that some Z-line components may be preferentially localized to the Z-line/I-band boundary (e.g., filamin, MLP) or more prominent in the Z-lines of peripheral myofibrils. Copyright 2001-2004, E.C. Niederhoffer. All Rights Reserved.

SarcolemmaSarcolemma

(http://cellbio.annualreviews.org/cgi/content/full/18/1/637)A schematic model of the cytoskeletal filament linkages at the sarcolemma of striated muscle. Four major cytoskeletal/membrane junctions are depicted: (a) cadherin-based linkages to actin and intermediate filaments (desmin); (b) integrin-based focal adhesions; (c) dystroglycan complex (DGC); and (d) spectrin-based membrane cytoskeleton. The cadherin-based fascia adheren at the intercalated disc couples neighboring cardiomyocytes (through homotypic interactions) and tethers the contractile apparatus to the muscle termini. Desmosomes are a second cadherin-based junction that anchor desmin filaments at the intercalated disc. Connections between intermediate filament proteins and the membrane may occur through a plectin/{alpha}ß-crystallin complex or via an association with DGC via dystrobrevin. Integrin-based focal adhesions and the DGC act as transmembrane receptors for ECM components (e.g., laminin) and link the extracellular surface with the actin cytoskeleton. Integrins associate with talin, {alpha}-actinin, vinculin and N-RAP to form a strong mechanical link to actin filaments. Integrins could directly interact with {alpha}-actinin and/or other components not depicted here to mediate a connection with actin. The DGC consists of the transmembrane complex {alpha}/ß-dystroglycan, dystrophin, the sarcoglycans, and other components not depicted here. Spectrin is enriched at costameres, and is an important component of the membrane cytoskeleton. It is linked to the membrane through ankyrin and probably the Na,K-ATPase transmembrane protein. Spectrin may have an additional role in anchoring the contractile apparatus to the membrane though an interaction with MLP. Importantly, all of these linkage complexes can bind to the submembraneous actin ({gamma}-actin) and are probably interlinked through this association as well as other unknown interactions.


Role of calciumRole of calcium

• Muscle contraction• troponin C• Glycogen breakdown• calmodulin (activates phosphorylase b

kinase)• Citric acid cycle activation• pyruvate dehydrogenase complex• isocitrate dehydrogenase -ketoglutarate dehydrogenase

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Muscle fiber type Muscle fiber type and its role in and its role in

movementmovement

Fiber Contraction Speed: Fiber Contraction Speed: Fast & Slow Twitch muscle Fast & Slow Twitch muscle

fibersfibers


•Glycogen?•Myoglobin?•Capillary?•Diameter?

<<>>>><<

Metabolism? Myosin ATPase activity?

Time to develop max tension?Ca++-ATPase activity in SR?

Contraction duration?Endurance?

Use?

““RED” muscle fiberRED” muscle fiber

•Glycogen?•Myoglobin?•Capillary?•Diameter?

>><<<<>>

Metabolism? Myosin ATPase activity?

Time to develop max tension?Ca++-ATPase activity in SR?

Contraction duration?Endurance?

Use?

““WHITE” muscle fiberWHITE” muscle fiber

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Muscle contraction inMuscle contraction incontrol of movementcontrol of movement

Bear, Connors, Paradiso; Neuroscience. Exploring the Brain

Spinal ReflexSpinal Reflex

Graded Muscle Graded Muscle ResponsesResponses

• Graded muscle responses are:– Variations in the degree of muscle

contraction– Required for proper control of skeletal

movement

• Responses are graded by:– Changing the strength of the stimulus – Changing the frequency of stimulation



Recruitment of motor unitsRecruitment of motor units


Motor unit Motor unit stimulationstimulation

• Subthreshold stimulus

• Threshold stimulus

• Submaximal stimulus

• Maximal stimulus

• Supramaximal stimulus

• Subthreshold stimulus

• Threshold stimulus

• Submaximal stimulus

• Maximal stimulus

• Supramaximal stimulus

0

1

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3

3

MECHANOMYOGRAMMECHANOMYOGRAM

Number of motor unit Number of motor unit recruitedrecruited

twitch

Stimulus Intensity and Muscle Stimulus Intensity and Muscle TensionTension

Figure 9.15 (a, b)Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings


Treppe: The Staircase Treppe: The Staircase EffectEffect

Figure 9.16Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings


Coordinating the Fibers: Coordinating the Fibers: Summation to TetanusSummation to Tetanus

Figure 12-17: Summation of contractions Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings


The effect of sarcomere The effect of sarcomere length length

on tensionon tension

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CROSS BRIDGECROSS BRIDGEPOWER STROKE

MECHANIC FORCE

BODY MOVEMENT

CONTRACTION of MUSCLECONTRACTION of MUSCLE

MOTOR NERVEMOTOR NERVE

FREQUENCY & FREQUENCY & INTENSITY ofINTENSITY ofSTIMULUS/ISTIMULUS/I

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ncs & aaj

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