Ganong's Review of Medical Physiology, 23rd Edition

94
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