Skeletal System Notes

Skeletal System

Websites for HEEEELLLPPPP!!!

1. http://www.bio.psu.edu/people/faculty/strauss/anatomy/skel/skeletal.htm

2. http://depts.washington.edu/bonebio/bonAbout/structure.html3. http://www.leeds.ac.uk/chb/lectures/anatomy3.html4. http://homepage.mac.com/myers/misc/bonefiles/bonestruct.html5. http://www.bbc.co.uk/science/humanbody/body/interactives/3djigsa

w_02/index.shtml?skeleton6. http://www.bartleby.com/107/17.html7. http://sv.berkeley.edu/showcase/pages/bones.html8. http://www.innerbody.com/image/skelfov.html9. http://www.medtropolis.com/VBody.asp10.http://wps.aw.com/bc_martini_eap_4/40/10466/2679495.cw/content

/index.html

2 Divisions of Skeletal System

• Axial skeleton• Appendicular skeleton

Axial Skeleton

• 80 bones • Consist of bones in the:

– Skull– Vertebral Column– Thorax– Hyoid

Appendicular

• 126 bones• Bones in the:

– Shoulders– Upper limbs– Lower limbs– Pelvic girdle

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

Classification of Bones: By Shape

• Long bones – longer than they are wide (e.g., humerus)

Figure 6.2a

Classification of Bones: By Shape

• Short bones– Cube-

shaped bones of the wrist and ankle

– Bones that form within tendons

Figure 6.2b

Classification of Bones: By Shape

• Flat bones – thin, flattened, and a bit curved (e.g., sternum, and most skull bones)

Figure 6.2c

Classification of Bones: By Shape

• Irregular bones – bones with complicated shapes (e.g., vertebrae and hip bones)

Figure 6.2d

Classification of Bones: By Shape

• Sesamoid – knee bone (e.g., patella only)

Figure 6.2d

Patella

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

Function of Bones

• Mineral storage – reservoir for minerals, especially calcium and phosphorus

• Blood cell formation – (hematopoiesis) occurs within the marrow cavities of bones

Gross Anatomy of Bones: Bone Textures

• Compact bone – dense outer layer

• Spongy bone – honeycomb of trabeculae filled with bone marrow

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

Typical Long Bone Structure

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)

Structure of Long Bone

Figure 6.3

Structure of Long Bone

Figure 6.3a

Structure of Long Bone

Figure 6.3b

Structure of Long Bone

Figure 6.3c

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)

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

Bone Surface Markings

Meatus PASSAGE extending within a bone (ex. External auditory meatus)

Bone Surface Markings

• Fossa DITCH or shallow depression on a bone (ex. Mandibular fossa of temporal bone)

Bone Surface Markings

• Head rounded projection that forms a joint & supported (ex. Head of femur)

Bone Surface Markings

• Crest Prominent ridge (ex. illiac crest of pelvic bone)

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

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Microscopic Structure of Bone: Compact Bone

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

of compact bone

Parts of the Osteon (Haversian System)

– Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen

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

– 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

Microscopic Structure of Bone: Compact Bone

• Lacuna – small cavities in bone that contain osteocytes

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

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Hyoid Bone

• Only bone that does not articulate directly with another bone

• Attachment point for neck muscles and assists during swallowing and speech

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)

Vertebral Column

Figure 7.13

Bony Thorax (Thoracic Cage)

• Functions– Protects the heart & lungs

Comparison of Male and Female Pelves

Developmental Aspects: Fetal Skull

• Bones are not fully connected and held together by fontanels

• Fontanels– Unossified membranes – 4: anterior, posterior, mastoid, and sphenoid

Developmental Aspects: Fetal Skull

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 Clip

Homeostasis of Bone Tissue

Nutrition1. Vitamin D absorbs calcium

in small intestine2. Vitamin A bone resorption3. 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)

Developmental Aspects of Bones

• By age 25, all bones are ossified

• Until age of 25 osteoblasts dominate• Mid-old age osteoclasts dominate

Developmental Aspects: Old Age

• Intervertebral discs become thin• Loss of stature by several centimeters is

common after age 55 • All bones lose mass

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

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

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

Stages of Endochondral Ossification

Figure 6.8

Formation ofbone collararound hyalinecartilage model.

Hyalinecartilage

Cavitation ofthe hyaline carti-lage within thecartilage model.

Invasion ofinternal cavitiesby the periostealbud and spongybone formation.

Formation of themedullary cavity asossification continues;appearance of sec-ondary ossificationcenters in the epiphy-ses in preparationfor stage 5.

Ossification of theepiphyses; whencompleted, hyalinecartilage remains onlyin the epiphyseal platesand articular cartilages.

Deterioratingcartilagematrix

Epiphysealblood vessel

Spongyboneformation

Epiphysealplatecartilage

Secondaryossificatoncenter

Bloodvessel ofperiostealbud

Medullarycavity

Articularcartilage

Spongybone

Primaryossificationcenter

Bone collar

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5

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Functional Zones in Long Bone Growth

• Growth zone – cartilage cells undergo mitosis, pushing the epiphysis away from the diaphysis

“This is how you grow