The skeletal system contains 206 bones that are categorized into four basic shapes: long bones, short bones, flat bones, and irregular bones. The skeletal system functions to provide support, protect organs, regulate blood calcium levels, and allow for muscle attachment. Bones form through two processes - intramembranous ossification which forms flat bones, and endochondral ossification which replaces cartilage. The muscular system contains three main types of muscle: skeletal, cardiac, and smooth muscle. Skeletal muscle is attached to bones by tendons and forms the bulk of muscle mass controlled voluntarily.

3. The skeletal System
• 206 bones
• 4 basic shapes (long bones femur, short bones
wrist and ankle, flat bones skull and scapula,
irregular bones vertebrae)
• 80 axial skeleton
• 126 appendicular skeleton

4. General Shapes Of Bones
• Long bones (e.g., humerus, femur)
• Short bones (e.g., carpals, tarsals, patella
• Flat bones (e.g., parietal bone, scapula, sternum)
• Irregular bones (e.g., vertebrae, hip bones)

6. Function of bone
• Support
• Protection
• Homeostatic regulation of blood calcium
• Blood cell formation and muscle
attachment

7. Formation of the Skeleton
• Before week 8, the skeleton of a
human embryo consists of
fibrous membanes and hyaline
cartilage
• Intramembranous ossification –
bone develops from a fibrous
connective tissue membrane.
The flat bones of the skull
(frontal, parietal, temporal,
occipital) and the clavicles are
formed this way.
• Endochondral ossification – bone
forms by replacing hyaline
cartilage, uses hyaline cartilage
“bones” as patterns

8. The Muscular System
• Muscle is a soft tissues found in most animal. It is
formed during embryonic development.
• Muscles are responsible for all types of body
movement – they contract or shorten and are the
machine of the body
Three basic muscle types are found in the body
• Skeletal muscle
• Cardiac muscle
• Smooth muscle

10. Muscle Diagram Human Body System

11. Skeletal Muscle Characteristics
• Most are attached by tendons to bones
• Cells are multinucleate
• Striated – have visible banding
• Voluntary – subject to conscious control
• Cells are surrounded and bundled by
connective tissue = great force, but tires easily

12. Smooth Muscle Characteristics
• Has no striations
• Spindle-shaped cells
• Single nucleus
• Involuntary – no
conscious control
• Found mainly in the walls
of hollow organs
• Slow, sustained and
tireless

13. Cardiac Muscle Characteristics
• Has striations
• Usually has a single
nucleus
• Joined to another muscle
cell at an intercalated
disc
• Involuntary
• Found only in the heart
• Steady pace!

17. Structure of Skeletal muscles
• Skeletal muscles are composed of clusters of
muscle cells.
–Muscle fibers
–Myofibers
–Myocytes
• A muscle consists of packages of muscle cells
called fascicles
• A muscle cell is long and spindle shaped

18. Structure of Skeletal muscles
• Cell structure
– Muscles cells contain many nuclei
– The plasma membrane→ sarcolemma
– The cytoplasm→ sarcoplasm
– Length
– ranges from 0.1cm to more the 30cm in
length
– Diameter
– ranges from 0.001cm to 0.01cm in
diameter
• Myofibrils→
– elongated protein molecules
– aligned in parallel arrangements
– extend the full length of the cell

21. Structure of Skeletal muscles
• The myofibril consists of protein chains
called myofilaments
– Myofilaments have a symmetrical,
alternating pattern of thick and thin
elements

22. Skeletal Muscle Actin
• The thin myofilament (F-actin, filamentous actin)
– made up of two helically intertwined chains of G-actin
(globular actin) units.
• Other proteins that bind to the actin molecules:
• Tropomyosin
• The Troponin complex→ made up of three
members

23. Development of skeletal muscle
Skeletal muscle begins to differentiate when
mesenchymal cells called myoblasts align and fuse
together to make longer, multinucleated tubes called
myotubes. Myotubes continue differentiating to form
functional myofilaments and the nuclei are displaced
against the sarcolemma. Part of the myoblast
population does not fuse and differentiate, but remains
as a group of mesenchymal cells called muscle satellite
cells located on the external surface of muscle fibers
inside the developing external lamina. Satellite cells
proliferate and produce new muscle fibers following
muscle injury.

24. Development of skeletal muscle

25. Organization of skeletal muscle
1) An entire skeletal muscle is enclosed within a
dense connective tissue layer called the epimysium
continuous with the tendon binding it to bone.
2) Each fascicle of muscle fibers is wrapped in
another connective tissue layer called the
perimysium.
3) Individual muscle fibers (elongated multinuclear
cells) is surrounded by a very delicate layer called
the endomysium, which includes an external lamina
produced by the muscle fiber (and enclosing the
satellite cells) and ECM produced by fibroblasts.

28. Regeneration of muscle
• Muscle regeneration is the process
by which damaged skeletal, smooth
or cardiac muscle undergoes
biological repair and formation of
new muscle in response to death of
muscle cells.

29. REGENERATION OF MUSCLE
• Although skeletal muscle cells do not have the
capability of mitotic activity, the tissue can
regenerate because of the presence of satellite
cells. These cells may undergo mitotic activity,
resulting in hyperplasia, subsequent to muscle
injury. Under certain other conditions, such as
"muscle building," satellite cells may fuse with
existing muscle cells, thus increasing muscle mass
during skeletal muscle hypertrophy.

30. Skeletal muscle cells regulate their number and
their size by the secretion of a member of the
transforming growth factor-β (TGF-β)
superfamily of extracellular signaling molecules,
myostatin. Certain mutant mice, whose skeletal
muscle fibers cannot produce myostatin have
enormous muscles that not only have many
more cells but whose muscle cells are much
larger than those of normal mice.