Page 187 - Anatomy and Physiology of Farm Animals, 8th Edition

172 / Anatomy and Physiology of Farm Animals

he basis for movement in living cells is multinucleated cell with visible striations.
Immediately beneath the outer cell mem-
Tcontractile proteins, which can convert
VetBooks.ir chemical energy into the mechanical energy brane (sarcolemma) are numerous nuclei,
reflecting the end‐to‐end fusion of shorter
of tension and motion. Muscle cells are
highly specialized for contraction, and their primitive muscle cells during development.
primary constituents are contractile pro- The interior of the fiber is packed with
teins. However, proteins with contractile elongated protein strands (myofibrils), and
properties have also been extracted from filling the clefts and spaces between these
many other types of cells. For example, such strands is an extensive network of smooth
proteins are responsible for the migration of endoplasmic reticulum (sarcoplasmic
some white blood cells from capillaries into reticulum) and associated tubular invagi-
peripheral tissues, for the movements of nations of sarcolemma (transverse tubules,
mitochondria, and for the movement of the or T tubules) (Fig. 9‐1). As you have already
cilia on some epithelial cells. noticed, many of the structures related to
muscle are modified with the affix “sarco”
from the Greek word sark, meaning flesh.
Skeletal Muscle Although skeletal muscle fibers look
virtually identical on routine histologic stains
Structure (see Fig. 1‐10), their biochemical differences
can be appreciated with histochemical tech-
The skeletal muscle fiber (also called volun- niques. Staining for the activity of myosin
tary striated muscle fiber) is actually a long, adenosine triphosphatase (ATPase), the

Myo brils
Sarcolemma

Terminal
Triad of the cisternae
reticulum
Z line
Transverse
tubule
Mitochondrion

A band

Sarcoplasmic
reticulum

I band Transverse
tubule

Sarcotubules
Figure 9-1. The myofibrils of a skeletal muscle cell are surrounded by sarcoplasmic reticulum. T tubules
extend into the sarcoplasm from the sarcolemma to surround the myofibrils. Source: Guyton and Hall,
2006. Reproduced with permission of Elsevier.