copyright © 2007 pearson education, inc., publishing as benjamin cummings twitch time course...

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Twitch time course

Duration of twitch is largely governed by rate of sequestration of calcium into SR


X-ray crystal structures

In the beginning of the movie, the myosin heads are in the prestroke ADP-Pi state (yellow) and the

catalytic cores bind weakly to actin. Once a head docks properly onto an actin subunit (green),

phosphate (Pi) is released from the active site. Phosphate release increases the affinity of the

myosin head for actin and swings the converter/lever arm to the poststroke, ADP state

(transition from yellow to red). The swing of the lever arm moves the actin filament by ~100 Å; the exact distance may vary from cycle to cycle depending

upon the initial prestroke binding configuration of the myosin on actin. After completing the stroke, ADP

dissociates and ATP binds to the empty active site, which causes the catalytic core to detach from actin.

The lever arm then recocks back to its prestroke state (transition from red to yellow).

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-13

Phosphocreatine

Provides ATP at beginning of exercise needed for contraction


Muscle Fatigue

Locations and possible causes of muscle fatigue


Muscle Fiber Types

Fast-twitch glycolytic and slow-twitch oxidative muscle fibers


Length-Tension Relationships in Contracting Muscle

Figure 12-16


Summation of Contractions

Figure 12-17a



Figure 12-17b



Figure 12-17d


Motor Units


Isotonic and Isometric Contractions


Series Elastic Elements in Muscle


Muscle Contraction

Duration of muscle contraction of the three types of muscle

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-25a

Types of Smooth Muscle


Types of Smooth Muscle

Figure 12-25b


Smooth Muscle

Has longer actin and myosin filaments

Myosin ATPase activity much slower

Actin more plentiful

Has less sarcoplasmic reticulum IP3-receptor channel is the primary calcium channel

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-27a–b

Anatomy of Smooth Muscle

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, step 1

Smooth Muscle Contraction

ECF

Ca2+Ca2+

Sarcoplasmicreticulum Intracellular Ca2+

concentrations increase when Ca2+ enters cell and is released from sarcoplasmic reticulum.

Ca2+

11

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, steps 1–2


ECF

Ca2+Ca2+

Ca2+

Sarcoplasmicreticulum

CaM Pi

Pi

CaM

Intracellular Ca2+


Ca2+ binds to calmodulin (CaM).

Ca2+

1

2

1

2



ECF

Ca2+Ca2+

Ca2+


CaM Pi

Pi

ActiveMLCK

CaM

Intracellular Ca2+



Ca2+–calmodulin activates myosin lightchain kinase (MLCK).

Ca2+

InactiveMLCK

1

2

3

1

2

3



ECF

Ca2+Ca2+

Ca2+


CaM Pi

Pi

ActiveMLCK

CaM

ADP +

Active myosinATPase

PP

Intracellular Ca2+




MLCK phosphorylates light chains in myosinheads and increases myosin ATPase activity.

ATP

Ca2+

Inactive myosin

InactiveMLCK

1

2

3

4

1

2

3

4



ECF

Ca2+Ca2+

Ca2+


CaM Pi

Pi

ActiveMLCK

CaM

ADP +

Active myosinATPase

Actin

PP

Intracellular Ca2+




MLCK phosphorylates light chains in myosinheads and increases myosin ATPase activity.

Active myosin crossbridges slide along actin and create muscle tension.

ATP

Increasedmuscletension

Ca2+

Inactive myosin

InactiveMLCK

1

2

3

4

5

1

2

3

4

5

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-29, step 1

Relaxation in Smooth MuscleCa2+

ECFCa2+

Ca2+Ca2+

Na+

Na+


Free Ca2+ in cytosol decreases whenCa2+ is pumped out of the cell or backinto the sarcoplasmic reticulum.

1

1

ATP

ATP



ECFCa2+

Ca2+Ca2+

Ca2+

Na+

Na+

CaM

CaM



Ca2+ unbinds from calmodulin (CaM).

1

2

1

2

ATP

ATP



ECFCa2+

Ca2+Ca2+

Ca2+

Na+

Na+

CaM

CaM

Inactive myosin Myosin ATPaseactivity decreases.

ADP +

Myosinphosphatase

PP

ATP




Myosin phosphatase removes phosphate from myosin, which decreases myosin ATPase activity.

1

2

3

1

2

3

ATP

ATP



ECFCa2+

Ca2+Ca2+

Ca2+

Na+

Na+

CaM

CaM

Inactive myosin Myosin ATPaseactivity decreases.

ADP +

Myosinphosphatase

PP

ATP

Decreasedmuscletension




Myosin phosphatase removes phosphate from myosin, which decreases myosin ATPase activity.

Less myosin ATPase results in decreased muscle tension.

1

2

3

4

1

2

3

4

ATP

ATP


Control of Smooth Muscle Contraction


Smooth Muscle

Smooth muscle cells contain stretch-activated calcium channels Open when pressure or other force distorts cell

membrane

Known as myogenic contraction


Smooth Muscle Regulation

Many smooth muscles have dual innervation Controlled by both sympathetic and parasympathetic

neurons

Hormones and paracrines also control smooth muscle contraction Histamine constricts smooth muscle of airways

copyright © 2007 pearson education, inc., publishing as benjamin cummings twitch time course...

Documents

pearson education

benjamin cummings figure

types of muscle slide

contraction slide

b slide

types of smooth muscle

sr slide

d slide