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SECTION II
Physiology of Nerve & Muscle Cells
The contractile mechanism in skeletal muscle largely
depends on the proteins
myosin-II, actin, tropomyosin,
and
troponin.
Troponin is made up of three subunits:
troponin I,
troponin T,
and
troponin C.
Other important proteins in
muscle are involved in maintaining the proteins that partici-
pate in contraction in appropriate structural relation to one
another and to the extracellular matrix.
FIGURE 5–1
Mammalian skeletal muscle.
A single muscle fiber surrounded by its sarcolemma has been cut away to show individual
myofibrils. The cut surface of the myofibrils shows the arrays of thick and thin filaments. The sarcoplasmic reticulum with its transverse (T)
tubules and terminal cisterns surrounds each myofibril. The T tubules invaginate from the sarcolemma and contact the myofibrils twice in
every sarcomere. Mitochondria are found between the myofibrils and a basal lamina surrounds the sarcolemma.
(Reproduced with permission
from Kandel ER, Schwartz JH, Jessell TM [editors]:
Principles of Neural Science
, 4th ed. McGraw-Hill, 2000.)
Myofibril
Filaments
Mitochondrion
Terminal
cistern
Transverse
tubules
A
Sarcoplasmic
reticulum
Sarcolemma
(muscle fiber membrane)
Z disk Sarcomere
Thin filament
(F-actin)
Thick filament
(myosin)
Tropomyosin Troponin
Actin
B Z disk
C