3. cardiac muscle tissue

1. CARDIAC MUSCLE TISSUE
•Cardiac Muscle Tissue, or Heart
muscle as it is sometimes called, is
found in only one place in the body –
the walls of the heart. The actual
muscular wall of the heart is called the
myocardium. Cardiac muscle has a
very unique structure and could be
described as intermediate or “in
between” skeletal and smooth muscle
tissue.

2. •Cardiac muscle fibers
seem to branch, weave,
and merge with each
other, forming what
appears to be one
continuous,
multinucleated mass
(called a syncytium).
However, high
magnification shows
that each cardiac muscle
fiber is completely
bounded by its own
sarcolemma. So that
even though the fibers
do branch, they are not
continuous with adjacent
fibers.

3. •Schematic
drawings of such a
branching and
weaving structure
are as seen to the
right and show how
the muscle fibers
are shaped.

4. •A consequence of this
branching structure brings
about a very prominent
and identifying
characteristic of cardiac
muscle tissue. This is the
presence of dark bands
which cross the fibers at
intervals. These are called
intercalated discsand
they are formed when the
sarcolemmaof two (or
more) adjacent fibers or
branches come together
and overlap in an end to
end manner.

5. Another example of intercalated discs.

6. •Cardiac muscle fibers
have striations when
viewed under the
microscope; however,
they are not as dark as
those found in skeletal
muscle. This is due to
the myofibrils in
cardiac muscle being
arranged in an orderly
manner as with
skeletal muscle, but
the number, and
therefore the density
of the myofibrils is
less.
**(Note all the intercalated discs!)

7. •With respect
to another key
identifying
factor, each
cardiac muscle
fiber has one
nucleus
located deep
within the cell.
**(Note the faint striations
and the intercalated disc)
“Centrally” located, single nucleus

8. General Characteristics
1. Location -
Muscular wall of the
heart called the
myocardium

9. 2. Cell Type or
description -
Short fibers (0.05-
0.1 mm), branching,
weaving network
with overlapping
sarcolemma forming
intercalated discs

10. 3.Myofibrils -
-Fill cell from end to
end but less dense
than skeletal
-Orderly; with light
striations visible

11. 4.Location of
nucleus or
nuclei -
One oval
nucleus located
in the center of
the cell.

12. 5.Vascular
Supply and
relative rank -
-Dense blood
capillary network
with continuous
supply
-Ranks 1
st
among
muscle tissues

13. 6.Description of
Contraction and
Control Factor –
-Rhythmic (inherent),
rapid, contractions
of fibers
coordinated.
-Involuntary
contraction
7.Alternative
names-
Involuntary, striated or
Heart muscle

14. Microscopic Views of Cardiac
Muscle (Schematic)

15. Longitudinal View (long Axis)
**(Note the light striations, centrally located nucleus, and intercalated discs)

16. Another Longitudinal View
Note the branching, weaving network (black arrow), single, centered
nucleus (green arrow), and the intercalated discs (yellow arrow).

17. Cross-sectional View (short axis)
Note the single, centrally located nucleus

18. Another Cross-sectional View

19. Additional Pictures of Cardiac
Muscle

20. 1.What “view” is this?
2.Arrow #1 is what?
3.Arrow #2 is what?
4.Are striations visible?
#1
#2

22. A comparison between
cardiac (top) and
skeletal (bottom).

23. What tissue is this?
How did you know?

24. How did you know what it was?
•1. Multiple peripheral nuclei
•2. Parallel fibers
•3. Strongly visible striations

25. What tissue is this?
How did you know?

26. How did you know what it was?
•1. Intercalated discs
•2. Branching, weaving network of cells
•3. Single nucleus in the center of fiber
•4. Lightly visible striations