Muscles and Muscle Tissue
of an average body cell—and their length is phenomenal, some
up to 30 cm long. Teir large size and multiple nuclei are not
surprising once you learn that hundreds of embryonic cells fuse
to produce each ﬁber.
, the cytoplasm of a muscle cell, is similar to the
cytoplasm of other cells, but it contains unusually large amounts
(granules of stored glycogen that provide glucose
during muscle cell activity) and
, a red pigment that
stores oxygen. Myoglobin is similar to hemoglobin, the pigment
that transports oxygen in blood.
In addition to the usual organelles, a muscle cell contains
three structures that are highly modiﬁed: myoﬁbrils, sarcoplas-
mic reticulum, and ± tubules. Let’s look at these structures more
closely because they play important roles in muscle contraction.
A single muscle ﬁber contains hundreds to thousands of rod-
that run parallel to its length (Figure 9.2b). Te
myoﬁbrils, each 1–2 μm in diameter, are so densely packed in
the ﬁber that mitochondria and other organelles appear to be
squeezed between them. Tey account for about 80% of cellular
, the muscle’s connective tissue
wrappings extend beyond the muscle either as a ropelike
(Figure 9.1a) or as a sheetlike
sis). Te tendon or aponeurosis anchors the muscle to
the connective tissue covering of a skeletal element (bone or
cartilage) or to the fascia of other muscles.
Indirect attachments are much more common because of
their durability and small size. ±endons are mostly tough colla-
gen ﬁbers which can withstand the abrasion of rough bony pro-
jections that would tear apart the more delicate muscle tissues.
Because of their relatively small size, more tendons than ﬂeshy
muscles can pass over a joint—so tendons also conserve space.
Before moving on to microscopic anatomy, you may want to
review the top three rows of ±able 9.1.
Microscopic Anatomy of a Skeletal
Each skeletal muscle ﬁber is a long cylindrical cell with multiple
oval nuclei just beneath its
or plasma membrane
. Skeletal muscle ﬁbers are huge cells. Teir diam-
eter typically ranges from 10 to 100 μm—up to ten times that
(between individual muscle fibers)
Perimysium wrapping a fascicle
in middle of
Connective tissue sheaths of skeletal muscle: epimysium, perimysium,
Photomicrograph of a cross section of part of a skeletal muscle (30
(For a related image, see
A Brief Atlas of the Human Body
, Plate 29.)