Page 76 - Color_Atlas_of_Physiology_5th_Ed._-_A._Despopoulos_2003

A. The sarcotubular system of myocytes (muscle fibers)
T system Sarcoplasmic
AP (transverse tubules) reticulum
(longitudinal tubules)
AP

Sarcolemma
(cell membrane)
Triads

Mitochondrion Contraction of Striated Muscle I

(After Porter and
Franzini-Armstrong)
B. Ca as mediator between electrical stimulus and contraction
2+
T system
– 90 mV DHPR RYR1 Plate 2.12
Rest AP Sarco-
plasmatic
Ca 2+ reticulum
Low [Ca ] i
2+
Stimulus 2+
[ Ca ] i 2 Skeletal Cytosol
AP muscle
Contraction
DHPR
0 10 20 30 ms with Ca 2+
channel
AP RYR2
+30 mV Ca 2+
2+
High [Ca ] i
3 Myocardium
2+
1 Ca release
C. Sliding filaments
Actin-myosinII binding
Strong Weak Strong
Myosin II ATP P i
P i
ADP ATP
a a a b

Actin 4nm 36nm or multiple
1 Strong binding 2 Work phase 3 Resting phase (ca. 90% of time; other 63
(ca.10% of time) myosin heads are meanwhile active)
Despopoulos, Color Atlas of Physiology © 2003 Thieme
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