The skeletal system is divided into the axial skeleton and appendicular skeleton. The axial skeleton includes the bones of the skull, vertebral column, thorax, and hyoid. The appendicular skeleton includes the bones of the shoulders, upper limbs, lower limbs, and pelvic girdle. Bones are classified based on their shape as long, short, flat, irregular, or sesamoid. Bones provide structure, protection, movement, mineral storage, and blood cell formation. The microscopic structure of compact bone consists of osteons (Haversian systems) containing lacunae and canaliculi. Bones develop through either intramembranous or endochondral ossification.

1. Skeletal
System

2. Websites for HEEEELLLPPPP!!!
1. http://www.bio.psu.edu/people/faculty/strauss/anatomy/skel/skeletal.
htm
2. http://depts.washington.edu/bonebio/bonAbout/structure.html
3. http://www.leeds.ac.uk/chb/lectures/anatomy3.html
4. http://homepage.mac.com/myers/misc/bonefiles/bonestruct.html
5. http://www.bbc.co.uk/science/humanbody/body/interactives/3djigsa
w_02/index.shtml?skeleton
6. http://www.bartleby.com/107/17.html
7. http://sv.berkeley.edu/showcase/pages/bones.html
8. http://www.innerbody.com/image/skelfov.html
9. http://www.medtropolis.com/VBody.asp
10.http://wps.aw.com/bc_martini_eap_4/40/10466/2679495.cw/content/
index.html

3. 2 Divisions of Skeletal System
• Axial skeleton • Appendicular skeleton

4. Axial Skeleton
• 80 bones
• Consist of bones in the:
– Skull
– Vertebral Column
– Thorax
– Hyoid

5. Appendicular
• 126 bones
• Bones in the:
– Shoulders
– Upper limbs
– Lower limbs
– Pelvic girdle

8. 206 Bones????• 24 Ribs
• 1 Sternum
• 26 Vertebrae
• 56 Phalanges
• 2 Clavicles
• 2 Scapula
• 2 Humerus
• 2 Radius
• 2 Ulna
• 2 Femur
• 2 Tibia
• 2 Fibula
• 2 Patella
• 22 cranial/facial
• 14 Tarsals
• 16 Carpals
• 10 metatarsals
• 10 metacarpals
• 2 pelvic bones
• 1 hyoid
• 6 ear ossicles

10. Classification of Bones: By
Shape
• Long bones
– longer
than they
are wide
(e.g.,
humerus)
Figure 6.2a

11. Classification of Bones: By Shape
• Short bones
– Cube-
shaped
bones of the
wrist and
ankle
– Bones that
form within
tendons
Figure 6.2b

12. Classification of Bones: By Shape
• Flat bones
– thin,
flattened,
and a bit
curved
(e.g.,
sternum,
and most
skull bones)
Figure 6.2c

13. Classification of Bones: By Shape
• Irregular
bones –
bones with
complicate
d shapes
(e.g.,
vertebrae
and hip
bones)
Figure 6.2d

14. Classification of Bones: By Shape
• Sesamoid
– knee
bone (e.g.,
patella
only)
Figure 6.2d
Patella

15. Function of Bones
• Support – form the framework
• Protection – provide a protective case for
the brain, spinal cord, and vital organs
• Movement – provide levers for muscles

16. Function of Bones
• Mineral storage – reservoir for minerals,
especially calcium and phosphorus
• Blood cell formation – (hematopoiesis)
occurs within the marrow cavities of bones

17. Gross Anatomy of Bones: Bone
Textures
• Compact bone –
dense outer layer
• Spongy bone –
honeycomb of
trabeculae filled with
bone marrow

18. Spongy Bone
• Does NOT contain osteons (structural units)
• Made up of trabeculae (irregular latticework)
• Btw. spaces of trabeculae is filled with red bone
marrow
• Only site of RED bone marrow: (Forms blood cells)
• Vertebrae
• Skull
• Hips
• Ribs
• Sternum
• Ends of long bones

19. Typical Long Bone Structure

20. Bone Structure –
Typical Long Bone
• Diaphysis = shaft, yellow bone marrow produced here
• Epiphyses = distal & proximal ends
• Epiphyseal line = remnant of epiphyseal plate
• Periosteum = outer, fibrous, protective covering,
essential for bone growth & diameter
• Endosteum = inner lining of medullary cavity, contains
bone forming cells (osteoblasts)
• Articular cartilage = pad of hyaline cartilage on the
epiphyses where long bones articulate or join, reduces
friction, absorbs shock
• Medullary cavity= space w/in diaphysis that contains
fatty yellow marrow (produces blood cells)

21. Structure of Long Bone
Figure 6.3

22. Structure of Long Bone
Figure 6.3a

23. Structure of Long Bone
Figure 6.3b

24. Structure of Long Bone
Figure 6.3c

25. Bone Tissue
• mineral salt makes them hard
– Magnesium salts
– Calcium salts
– Phosphorus salts
• collagen fibers gives them tensile
strength (the maximum stress the bone
can handle w/out breaking)

26. Bone Surface Markings
Foramen HOLE through which blood
vessels, nerves, or ligaments pass through (ex.
Foramen magnum)

27. Bone Surface Markings
Meatus PASSAGE extending within a bone
(ex. External auditory meatus)

28. Bone Surface Markings
• Fossa DITCH or shallow depression on a
bone (ex. Mandibular fossa of temporal bone)

29. Bone Surface Markings
• Head rounded
projection that forms a
joint & supported (ex.
Head of femur)

30. Bone Surface Markings
• Crest Prominent ridge (ex. illiac crest of pelvic
bone)

31. Chemical Composition of Bone:
Organic
• Osteo means bone
• Osteoblasts – bone-forming cells
• Osteocytes – mature bone cells
• Osteoclasts – large cells that resorb or
break down bone matrix

32. Microscopic Structure of Bone: Compact Bone

33. Microscopic Structure of Bone: Compact Bone
• Haversian system, or osteon – the structural unit
of compact bone

34. Parts of the Osteon (Haversian
System)
– Lamella – weight-bearing, column-like matrix tubes
composed mainly of collagen

35. – Haversian, or central canal – central channel
containing blood vessels and nerves

36. – Volkmann’s canals – channels lying at right
angles to the central canal, connecting blood
and nerve supply of the periosteum to that of
the Haversian canal

38. Microscopic Structure of Bone: Compact Bone
• Lacuna – small cavities in bone that
contain osteocytes

39. • Canaliculi – hairlike canals that connect
lacuna to each other and the central canal

40. Hyoid Bone
• Only bone that does not articulate directly
with another bone
• Attachment point for neck muscles and
assists during swallowing and speech

41. Vertebral Column
• Formed from 26 irregular bones
• Cervical vertebrae – 7 bones of the neck
• C1=Atlas
• C2=Axis
– Thoracic vertebrae – 12 bones of the torso
– Lumbar vertebrae – 5 bones of the lower back
– Sacrum –5 fused bones
– Coccyx- 3-5 fused bones (tailbone)

42. Vertebral Column
Figure 7.13

43. Bony Thorax (Thoracic Cage)
• Functions
– Protects the heart & lungs

44. Comparison of Male and Female Pelves

46. Developmental Aspects: Fetal
Skull
• Bones are not fully connected and held
together by fontanels
• Fontanels
– Unossified membranes
– 4: anterior, posterior, mastoid, and sphenoid

47. Developmental Aspects: Fetal
Skull

48. Bone Deposition
• Occurs where bone is injured or added
strength is needed
• Requires a diet rich in
– Protein
– Vitamins C, D, and A
– Calcium
– Phosphorus
– Magnesium
– Manganese

49. Homeostasis of Bone Tissue
Nutrition
1. Vitamin D absorbs calcium
in small intestine
2. Vitamin A bone resorption
3. Vitamin C Hardens bones
Hormones
1. Growth Hormone (from
pituitary gland) stimulates
growth
2. Parathyroid  Can increase
calcium levels (PTH)
3. Thyroid Can decrease
calcium levels (Calcitonin)

50. Developmental Aspects of
Bones
• By age 25, all bones are ossified
• Until age of 25 osteoblasts dominate
• Mid-old age osteoclasts dominate

51. Developmental Aspects: Old
Age
• Intervertebral discs become thin
• Loss of stature by several centimeters is
common after age 55
• All bones lose mass

52. Ossifications
• Intramembranous= forms flat bones
• Endochondral= forms all other bones
• http://health.howstuffworks.com/adam-
200125.htm
• http://commons.bcit.ca/biology/ossification/
files/ossification.html

53. Intramembranous ossification:
FLAT BONES
• Mesenchymal stem cells develop into
osteoblasts that secrete osteoids that
develop into bone tissue
• Spongy bone is formed followed by
compact bone surrounding medullary
cavity

54. Endochondral Ossification:
LONG BONES
1. Cartilage model formed
2. Primary ossification center formed in
diaphysis
3. Blood vessels, medullary cavity formed
4. Secondary ossification center formed in
epiphysis
5. Compact bone, articular cartilage, and
epiphyseal plate take shape

55. Stages of Endochondral
Ossification
Figure 6.8
Formation of
bone collar
around hyaline
cartilage model.
Hyaline
cartilage
Cavitation of
the hyaline carti-
lage within the
cartilage model.
Invasion of
internal cavities
by the periosteal
bud and spongy
bone formation.
Formation of the
medullary cavity as
ossification continues;
appearance of sec-
ondary ossification
centers in the epiphy-
ses in preparation
for stage 5.
Ossification of the
epiphyses; when
completed, hyaline
cartilage remains only
in the epiphyseal plates
and articular cartilages.
Deteriorating
cartilage
matrix
Epiphyseal
blood vessel
Spongy
bone
formation
Epiphyseal
plate
cartilage
Secondary
ossificaton
center
Blood
vessel of
periosteal
bud
Medullary
cavity
Articular
cartilage
Spongy
bone
Primary
ossification
center
Bone collar
1
2
3
4
5

56. Functional Zones in Long Bone
Growth
• Growth zone – cartilage cells undergo
mitosis, pushing the epiphysis away from
the diaphysis
“This is how you grow