Skeletal muscle is attached to bones and allows voluntary movement. It is composed of bundles of muscle fibers within connective tissue sheaths. Muscle fibers contain bundles of myofibrils which are made up of overlapping actin and myosin filaments. The overlapping filaments give skeletal muscle its striated appearance under microscopy due to alternating light and dark bands. Skeletal muscle fibers are long, cylindrical cells with multiple peripheral nuclei and can generate tremendous forces through voluntary contraction.

1. SKELETAL MUSCLE TISSUE
• Skeletal Muscle - Skeletal muscles
are all the muscles of the body that
are attached to the bones of the body
or “the skeleton”. Contraction of
these muscles permit movements of
the extremities, the eyeballs, the
tongue, the chest cavity, and much
more. These contractions are
consciously controlled or in other

2. words, the contraction of skeletal
muscle is voluntary. Forces
exerted by skeletal muscle are
tremendous. For example,
uncontrolled contractions
(spasming) of skeletal muscle
during seizure activity can snap
the diaphysis of a long bones, and
the human calf muscle can, on its
own, withstand forces of over a
ton.

3. • Terminology - A
specialized
terminology is
used to describe
muscles or muscle
tissue. The cell
membrane is
called the
sarcolemma, the
cytoplasm is called
the sarcoplasm,
the endoplasmic
reticulum is
sarcolemma

4. • called the
sarcoplasmic
reticulum, and the
muscle cell itself is
called a muscle
fiber. This
terminology is
specific to muscles
and is derived from
the Greek root
“sarkos” which
means “flesh”.
Muscle fiber
Sarcoplasmic
reticulum

5. • Structure -
Skeletal muscles
can be described as
“bundles within
bundles within
bundles”. Each
individual skeletal
muscle fiber
consists of bundles
of myofibrils and is
encased in a
connective tissue
called the
endomysium.

6. • Groups of skeletal
muscle fibers are in
turn gathered into
bundles which are
wrapped in more
connective tissue called
the perimysium.
These bundles are in
turn grouped together
and enclosed in a layer
of dense connective
tissue called the
epimysium which
forms individual
muscles.

7. • Each individual
muscle is wrapped
in a tough layer of
fibrous connective
tissue called the
fascia. These are
continuous with
tendons and the
periosteum of
bones.

8. • Muscle Fibers -
(myocytes or muscle
cells) - Muscle
fibers are the basic
unit of the muscle
itself. It is the
smallest functional
unit or cell that a
muscle can be
divided into. Muscle
fibers are made up of
smaller sub-units
called myofibrils.

9. • These are in turn
composed of
threadlike
myofilaments which
are composed of the
proteins actin and
myosin. Actin
filaments are thin and
appear as light bands
under the
microscope, while
myosin filaments are
thick and appear
dark.

10. • These have an
overlapping
structure and are
held together by
chemical cross
bridges. The
overlapping
structure gives
skeletal muscle a
banded or striped
look under the
microscope. ***(notice also the
multiple peripheral
nuclei seen in this
picture)

11. • These alternating
light and dark
bands are called
striations and give
skeletal muscle its
alternate name,
and more accurate
name, voluntary,
striated muscle.

12. • A closer look at the
striations reveals that the
myofibrils are composed
of repeating units of actin
and myosin called
sarcomeres. A
sarcomere represents the
smallest individual
contractile unit of a
muscle fiber. It is
measured from the point
where actin myofilaments
overlap to the next actin
overlap. The actin
overlap is called the “Z”
line, so a complete
sarcomere extends from
Z line to Z line.
Part of a myofibril

13. • The alternating dark
bands seen in a
typical light
microscope picture
are due to the thicker
areas of myosin
overlap within the
sarcomere.

14. General Characteristics
1. Location –
usually attached to
bone.
***(Note that the periosteum is continuous with
the tendon which is continuous with the fascia)

15. 2. Cell Type or
description –
long, cylindrical,
parallel fibers
arranged as bundles
within bundles.
(1-40mm long)
**(Note the construction – bundles of actin &
myosin form myofilaments; bundles of
myofilaments form myofibrils; bundles of
myofibrils form muscle fibers; bundles of
muscle fiber bundles form a muscle.)

16. 3. Myofibril
arrangement-
- Densely fill cell from
end to end
- Orderly; with dark
striations visible.

17. 4. Location of
nucleus
or nuclei –
Multiple, peripherally
located nuclei
**(Note the strong presence of striations)

18. 5. Vascular Supply
and relative rank
- Good blood
supply,variable with
activity
- Ranks 2nd
among
muscle tissues

19. 6. Description of
contraction and
control factor –
- Vigorous, of relatively
short duration, fibers
contract independently
- Voluntary contraction
7. Alternative
names –
Voluntary, striated

20. Microscopic Views of Skeletal
Muscle (Schematic)

21. Longitudinal View (long axis)
Note the parallel fibers and dark striations.

22. Note the parallel fibers, dark striations,
and the multiple, peripheral nuclei.
Another Longitudinal View

23. Cross-sectional View (short axis)
Note the peripherally located nuclei and the “bundled” look.
Perimysium
endomysium

24. Another Cross-sectional view
Note the peripherally located nuclei and the
cylindrical (circular ends) of the bundles.

25. Some slides include both views in
one!!
Area of cross-section
Area of longitudinal section

26. Important
Questions:
1. How can skeletal
muscle be
identified by
longitudinal
view?
2. How can skeletal
muscle be
identified by
cross-sectional
view?

27. Answer #1 -
In the longitudinal
view there will be
parallel fibers and
multiple peripheral
nuclei.
Answer #2 –
In the cross-sectional
view there will be
peripheral nuclei and
the appearance of
“cylindrical bundles”.

28. Additional Pictures of Skeletal
Muscle