CAP. 9. FISIOLOGIA CELULAR DEL MUSCULO ESQUELETICO, CARDIACO Y LISO

8/7/2019 CAP. 9. FISIOLOGIA CELULAR DEL MUSCULO ESQUELETICO, CARDIACO Y LISO

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Figure 9-1 Structure of skeletal muscle.

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Figure 9-2 Plasma membrane invaginations. A, The transverse tubules (T tubules) are extensions of the plasma membrane, penetrating the muscle cell at two points in

each sarcomere: the junctions of the A and I bands. B, Smooth muscle cells have rudimentary invaginations of the plasma membrane, called caveolae, contacting the

sarcoplasmic reticulum.


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Figure 9-3 EC coupling in skeletal muscle. A tetrad of four L-type Ca2+ channels on the T tubules faces a single Ca2+-release channel of the SR, so that each L-type

Ca2+ channel interacts with the foot of one of the four subunits of the Ca2+-release channel. Note that half of the Ca2+-release channels lack associations with L-type

Ca2+ channels. DHP, dihydropyridine.


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Figure 9-4 Structure of the sarcomere.


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Figure 9-5 Structure of thin and thick filaments.


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Figure 9-6 The role of Ca2+ in triggering the contraction of skeletal and cardiac muscle.


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Figure 9-7 The cross-bridge cycle in skeletal and cardiac muscle. Each cycle advances the myosin head by two actin monomers, or 11 nm.


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Figure 9-8 Mechanisms of Ca2+ removal from the cytoplasm.


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Figure 9-9 Isometric and isotonic contraction. A, Experimental preparation for study of muscle contraction under isometric conditions. B, Experimental preparation for

study of muscle contraction under isotonic conditions. C, The passive curve represents the tension that is measured at various muscle lengths before muscle contraction.

The total curve represents the tension that is measured at various muscle lengths during muscle contraction. Muscle length is expressed as the percent of "optimal"

length, that is, the length at which active isometric tension is maximal. D, The active tension is the difference between the total and the passive tensions in C. E, Each of

the three blue curves shows that the velocity of muscle shortening is faster if the muscle lifts a lighter weight-it is easier to lift a feather (left side of each curve/low load)

than to lift a barbell (right side of each curve/high load). The three blue curves also show that for any given velocity of shortening, a longer muscle can develop a greater

tension than can a shorter muscle.


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Figure 9-10 Microscopic measurements of cross-bridge force and displacement. A, An actin filament is attached at each end to a polystyrene bead. The optical tweezers,

a finely focused beam of laser light, can trap the bead at its focal point and physically move it. By adjusting the laser intensity, the experimenter can alter the strength of

the trap (i.e., the force with which the bead is held). In this experiment, two optical tweezers were used to suspend the actin filament above a coverglass. Attached to this

coverglass is a silica bead, and myosin molecules are bound to the bead. B, In an isotonic experiment, the force between the actin filament and the fixed myosin/silica

bead is kept constant by use of a stable laser intensity. The experimenter measures, as a function of time, the displacement of the polystyrene bead away from the

center of the trap. Thus, in one cross-bridge cycle, the myosin-actin interaction pulls the polystyrene bead 11 nm away from the center of the trap. C, In an

isometric experiment, the experimenter measures, as a function of time, the extra force that needs to be applied (i.e., increase in laser intensity) to keep the polystyrene

bead at a fixed position near the center of the trap. Thus, in one cross-bridge cycle, the myosin-actin interaction exerts a force of 5 pN. (Data from Finer JT,

Mehta AD, Spudich JA: Characterization of single actin-myosin interactions. Biophys J 1995; 68:291s-296s.)Downloaded from: StudentConsult (on 4 July 2010 07:07 PM)

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Figure 9-11 Frequency summation of skeletal muscle twitches.


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Figure 9-12 The motor unit and the motor neuron pool.


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Figure 9-13 Electrical coupling of cardiac myocytes.


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Figure 9-14 Smooth muscle organization. A, Each smooth muscle cell receives its own synaptic input. B, Only a few of the smooth muscle cells receive direct synaptic

input.


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Figure 9-15 Action potentials and slow waves in smooth muscle.


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Figure 9-16 EC coupling in smooth muscle.


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Figure 9-17 The role of Ca2+ in triggering the contraction of skeletal and cardiac muscle.


2005 Elsevier


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CAP. 9. FISIOLOGIA CELULAR DEL MUSCULO ESQUELETICO, CARDIACO Y LISO