MUSCULAR SYSTEM

Figure 50.37

Ball-and-socket joint

Head ofhumerus

Scapula

Hinge joint

Humerus

Ulna Ulna Radius

Pivot joint

Muscle

Bundle ofmuscle fibers

Nuclei

Single muscle fiber (cell)

Plasma membrane

MyofibrilZ lines

Sarcomere

Figure 50.26a

Z lines

Sarcomere

TEM0.5 m

Z line

M line

SarcomereZ line

Thickfilaments(myosin)

Thinfilaments(actin)

Figure 50.26b

Figure 50.30a

Synapticterminal

Axon ofmotor neuron

T tubule

Sarcoplasmicreticulum (SR)

Myofibril

Plasmamembraneof muscle fiber

SarcomereCa2 released from SR

Mitochondrion

Figure 50.29

TropomyosinActin Troponin complex

Ca2-binding sites

(a) Myosin-binding sites blocked

Ca2

Myosin-binding site

(b) Myosin-binding sites exposed

Thin filament

Myosin head (low-energy configuration)

ATP

Thickfilament

Myosin-binding sitesActin

High-energy configuration

ATP

ADP P i

ADPCross-bridge

Low-energy configuration

Thin filament movestoward center of sarcomere.

P i

3

4

2

1

5

P i

ADP

Figure 50.28a-5

Figure 50.31 Spinal cord Motorunit 1

Motorunit 2

Synaptic terminals

Nerve

Motor neuroncell body

Motor neuronaxon

Muscle

Tendon

Muscle fibers

2

Synaptic terminal of motor neuron

Synaptic cleft T tubule

Sarcoplasmicreticulum (SR)

Plasma membrane

ACh

Ca2 pumpCa2

Ca2

CYTOSOL

ATP

1

3

4

5

6

7

Figure 50.30b

Figure 50.32

Tetanus

Summation oftwo twitches

Singletwitch

Actionpotential Pair of

actionpotentials

Series of actionpotentials at

high frequency

Time

Ten

sio

n