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5-Bone Formation,

Markings, Fractures

Taft College Human Anatomy

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Bone Development: Formation and Growth

• Osteogenesis (ossification) – process of bone formation

• Cranial bones develop by a method called intramembranous ossification whereas…

• Other bones form by endochondralossification.

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IntramembranousIntramembranous OssificationOssification“within membrane”

• Bone forms directly within dense connective tissue membrane.

• Step 1 – mesechymal cells differentiate into osteoblasts that secrete bone

• Step 2 – bone forms between blood vessels randomly. Trabeculae form to create spongy bone. Mesenchymalcells condense on outer surface to form periosteum.

• Step 3 – Trabeculae thicken at periphery to form plates of compact bone.

• Where does intramembranousossification occur?

All flat bones of the skull and the clavicles form by this method.

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EndochondralEndochondral OssificationOssification““within cartilagewithin cartilage””

• Bone forms within a hyaline cartilage model– Cartilage built up in roughly the same shape of

bone, then broken down, reorganized and hardened (mineralized) to form bone. Model complete at 3 months of fetal development.

• Where does endochondral ossification occur? Most bones inferior to the skull

• Step 1 – hyaline cartilage formation via chondroblasts,which are surrounded by perichondrium, which becomes bone forming periosteum.

• Step 2 – cartilage calcifies in the center of diaphysis.Chondrocytes die due to calcification and nutrition cut off. Ends of bone still have healthy chondrocytes so the bone model enlarges.

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Primary center of ossification- area of initial calcification or bone formation. Primary center is located in the center of the bone (diaphysis).

• F.Y.I – Coincidence? The first of all of the primary centers of ossification to develop in the body occurs in the most frequently broken bone of the body = ??

• Collar bone = clavicle

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EndochondralEndochondral OssificationOssification““within cartilagewithin cartilage””

• Step 3 – Primary ossification center expands and periosteal bud containing nutrients artery and vein, bone marrow cells, osteoblasts and osteoclasts invades diaphysis.

• Osteoblasts begin to deposit bone matrix forming spongy trabeculae.

• Spongy bone is broken down by osteoclasts and the medullary cavity is formed.

7Secondary centers of ossification appear about the time of birth.

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EndochondralEndochondral OssificationOssification““within cartilagewithin cartilage””

• Step 4 – Blood vessels enter epiphysis and secondary ossification centers develop here about time of birth.

• Step 5 – Ossification of epiphyses.

• No cavity formation in the epiphyses.

• Hyaline cartilage remains covering the epiphysis articular surfaces

• Some cartilage becomes “trapped” between the two ossification centers creating the epiphyseal plate = growth plate.

• Bones lengthen and growth occurs as long as cartilage continues to be produced by the growth plate. ~age 18 in females, 21 in males.

• When the epiphyseal cartilage stops dividing, bone replaces the cartilage. This bony structure is called the epiphyseal line, a remnant of the once active epiphyseal plate.

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Bone Diseases• Achondroplasia in humans and pets. (sorry!)

– Genetic disorder - Chondrocytes fail to multiply and long bones grow slowly and stop growing early.

– Head and trunk are normal proportions. – = achondroplastic dwarf– Differs from pituitary dwarf.

• Osteoporosis– Bone reabsorption outpaces bone deposition.

Compact bone becomes thinner and less dense, spongy bone has fewer trabeculae.

– Vertebrae and hips are vulnerable to fracture. – Post menopausal women are at risk due to loss of

estrogen, less exercise, calcium poor diet.– Drink milk, exercise, take estrogen replacement

(female).

• Osteomyelitis– Bacterial infection of bone marrow.

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Fractures = breaks in bone or cartilage

• Complete fracture– Break extends

through bone – Simple fracture

• Bone breaks cleanly into 2 pieces w/ no penetration of skin

– Compound fracture• Broken bone

protrudes through soft tissue and skin

Simple Fracture

Compound Fracture

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Complete fracture Break extends completely through bone.Incomplete fracture (greenstick) One side of the bone is broken and the other side bends, as occurs with a green twig. Common in children whose bones are more flexible than adults.

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Blood clots to form a hematoma

Inflammation is apparent

Cell debris removed by phagocytes and osteoclasts

Blood vessels grow into clots

Collagen, fibrocartilage and hyaline produce callus to connect bone

3 weeks

Osteoblastsproduce spongy bone trabeculaejoining living and dead fragments

3-4 months

Bony callus remodeled to remove excess bony material to reshape bone and medullary cavity.

Repair of Bone Fractures

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Bones of the Skeleton

• 3 Categories of Bone markings = bone landmarks– Projections that are sites of muscle (tendon)

and ligament attachment.– Projections that help form joints– Depressions and openings allowing blood

vessels and nerves to pass

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Axial SkeletonAxial Skeleton –– skull, vertebral skull, vertebral column, and bony thoraxcolumn, and bony thorax

SkullSkull –– encloses and protects encloses and protects brain. Provides attachment for brain. Provides attachment for head and neck muscles. Mostly head and neck muscles. Mostly interlocking flat bones. interlocking flat bones.

VertebraeVertebrae –– individual bones of individual bones of the vertebral column act as a the vertebral column act as a supporting rod. Helps transfer supporting rod. Helps transfer trunk weight to lower limbs.trunk weight to lower limbs.

Divisions of the Skeleton

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Axial SkeletonAxial Skeleton –– skull, skull, vertebral column, and bony vertebral column, and bony thoraxthorax

RibsRibs –– Protects heart, lungs, Protects heart, lungs, and other thoracic organs. and other thoracic organs. Provides attachment for Provides attachment for many muscles for breathing many muscles for breathing and support, 12 pair.and support, 12 pair.

SternumSternum –– breast bonebreast bone

Divisions of the Skeleton

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AppendicularAppendicular SkeletonSkeleton –– the the limbs and their girdles which limbs and their girdles which append to the axial skeletonappend to the axial skeleton

Each limb is composed of a Each limb is composed of a girdle and 3 segments girdle and 3 segments connected by moveable joints.connected by moveable joints.

Upper limbsUpper limbs –– arm, forearm, arm, forearm, handhand

Shoulder girdle (pectoral)Shoulder girdle (pectoral) ––clavicle, scapula. Attaches clavicle, scapula. Attaches the upper limb to the trunk the upper limb to the trunk (axial skeleton)(axial skeleton)

Divisions of the Skeleton

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AppendicularAppendicular SkeletonSkeleton –– the the limbs and their girdles which limbs and their girdles which append to the axial skeletonappend to the axial skeleton

Lower limbsLower limbs –– thigh, leg, foot. thigh, leg, foot. Carries the entire weight of the Carries the entire weight of the erect body.erect body.

Pelvic girdlePelvic girdle –– consists of paired consists of paired hip bones. Attaches the lower hip bones. Attaches the lower limbs to the spine and supports limbs to the spine and supports visceral organs of pelvis. Full visceral organs of pelvis. Full weight of body passes through weight of body passes through this girdle to lower limbs.this girdle to lower limbs.

Divisions of the Skeleton

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Axial Skeleton - The SkullYou should have the bones of skull figured out by now – continue with landmarks!

8 Cranial BonesFrontal - 1 (2 In fetus)Parietal - 2Temporal - 2Occipital- 1Sphenoid - 1Ethmoid - 1

14 Facial BonesNasal 2Maxilla - 2 or MaxillaryZygomatic- 2Mandible - 1Lacrimal - 2Palatine - 2Inferior nasal conchae-2 Vomer 1

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Sutures = immoveable joints• Coronal suture- Unites frontal

bone and two parietal bones

• Squamosal suture- Unites parietal bones and temporal bone

• Sagittal suture- Unites two parietal bones

• Lambdoidal suture- Unites parietal bones and occipital bones, Y shaped

• Sutural (wormian) bonesSmall bones that occur within the sutures, especially within the lambdoidal suture. ~Approx 206 bones in adult

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Fontanels“soft spots”

• Allows skull to be compressed during birth and allows for brain growth.

• Anterior (frontal)– diamond shaped

• Posterior (occipital)– diamond shaped

• Sphenoid (anterior lateral)– small and irregular shaped

• Mastoid (posterior lateral)– irregularly shaped

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Axial Skeleton – Cont.

• Know the extent and the location of:• Vertebral column = (spine)• Sternum = breast plate• Ribs = 12 pair• Vertebrae – individual parts of column• Intervertebral foramina fig 7.13 p.164• Intervertebral discs fig 7.13 p. 164

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• Intervertebralforamina– lateral opening between 2

articulating vertebrae.– allows the spinal nerves

to exit the spine• Intervertebral discs

– ring of fibrocartilage w/ soft center between vertebrae

– found from the 2nd

vertebrae to the sacrum– form strong joints and

absorb vertical shockintervertebral foramina

articulating processintervertebral discs

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• Cervical vert. (7) C1-C7– neck region

• Thoracic vert. (12) T1-T12– Posterior to thoracic cavity– Articulate with ribs

• Lumbar vert. (5) L1-L5– Supports the lower back

• Sacral vert. (5) (fused)– Fused, immovable=sacrum

• Coccygeal vert. (3 or 4)– Fused, immovable (fused)– = coccyx

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Axial Skeleton –Vertebrae Types

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• Cervical curve– Concave = depression

= hollowed or arching in• Thoracic curve

– Convex = curving out or bulging outward

• Lumbar curve– Concave

• Sacral curve– Convex

• Coccygeal curve– Continuation sacral curve

• The curves increase the resilience of the spine, acting somewhat like a spring

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Axial Skeleton –Vertebral Curves

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• Body– Drum shaped, found on

anterior side, weight bearing region

• Spinous process– Posterior projection

• Transverse process– Projects laterally from each

side of the vertebral arch– Spinous and transverse

processes are attachment sites for:

• Muscles (movement)• Ligaments (stabilization)

• Vertebral foramen– Houses the spinal cord,

adipose and areolar C.T., and blood vessels

Vertebrae – Typical Features

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• Lightest and smallest• Vertebral foramen is large and triangular• Articulating surfaces allow for wide range of motion• Transverse foramina – hole in transverse process for

vertebral blood vessel passage• Bifid spinous process – split tip

• C7 – vertebra prominens = prominent “bump” surface anatomy landmark that helps identify other vertebrae

Specialized Features of

Cervical vertebrae

(7)

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C1 Atlas = 1st

Cervical Vertebra

• Supports the head superiorly• Lacks a body and a spinous

process• Superior articulating surfaces

– Articulates with occipital condyles– Allows for “yes” motion

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C2 Axis = 2nd

Cervical Vertebra

• Similar to other cervical vert. except for the knob-like dens that projects superiorly from body

• Body and dens (odontoidprocess)

• Dens allows head to rotate on the neck’s axis = “no”motion

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Specialized Features of Thoracic Vertebrae

(12)• Larger than cervical vert.• Longer and heavier spinous

processes pointed downward (inferiorly)

• Body roughly heart shaped• Articulation facets – facets

for articulating with ribs and other vertebrae

• All are faceted on transverse processes for rib articulation

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Specialized Features of Lumbar

Vertebrae (5)• Supports more body weight

than other vert. so large and sturdy

• Body is large and kidney bean shaped

• Spinous process– Short, flat, that project

straight posteriorly and well suited for muscle attachment

• Transverse process– Short, thick process that

projects laterally

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bifid

Vertebrae Identification

Bifid spinous process, transverse foramina present

Spinous process projects inferiorly, articulating facets for ribs

Spinous process projects posteriorly, Large size – body, spinous process

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bifid

Transverse Foramina

Spinous process projects inferiorly, articulating facets for ribs

Spinous process projects posteriorly, Large size – body, spinous process

Vertebrae Identification

Bifid spinousprocess, transverse foramina present

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Specialized Features of SacrumFusion of 5 vert. which begins in mid teens and completed by mid 20s

Serves as strong foundation for pelvic girdle (pelvic bones)

Sacral canal – opening in which vert. canal continues w/in sacrum

Auricular surface (Ala) – articulation with the 2 hip bones (ilium) to form the sacroiliac joints of the pelvis Auricle = earNote: the pelvic bones will also have an auricular surface.

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• Sternum – flattened breast bone, approx. 15 cm long, 3 pieces• Manubrium

– Triangle shaped, articulates laterally w/ clavicles and costal cartilage of the 1st

and 2nd ribs– Joined to body of sternum by fibrocartilage that forms sternal angle (references

point for 2nd rib)• Body

– Mid and largest portion, formed by 4 bones that fuse after puberty.– Side notches articulate w/ 2nd to 7th ribs

• Xiphoid process– Inferior, smallest portion, made up of hyaline cartilage that ossifies until about

40s.– Can puncture internal organs during CPR or sharp blow

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Axial skeleton (cont.)• Ribs

– 12 pairs that form flare in thoracic cage– Articulate with thoracic vert.– Increase in size (1 – 7) then decrease (8-12)

• True ribs = 1st – 7th pair– Superior 7 pairs attached

directly to sternum by costal cartilage

• False ribs = 8th – 12th pair– Inferior 5 ribs that attach to

sternum indirectly or no attachment

– Ribs 8-10 join via inferior cartilage connection to 7th.

• Floating ribs = 11th-12th pair– Rib pairs 11 and 12 have no

attachment to sternum

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= Hyaline

Cartilage

*Men and women both have 12 pair of ribs!

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Spinal Curvature Problems

• Scoliosis– Lateral curvature of spine, mostly

thoracic region, especially girls– Abnormal vert., unequal leg lengths,

muscle imbalance.• Kyphosis

– Exaggerated thoracic curve, “hunch back”

– Common in aged women due to fractures following osteoporosis

• Lordosis– Exaggerated lumbar curve, “sway back”– Temporary condition in obese men and

pregnant women attempting to preserve center of gravity

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Herniated Intervertebral Disc• Rupture of nucleus pulposus (gelatinous

rubber-like ball) through annulus fibrosus(fibrocartilage ring)

*There is no such thing as a “slipped” disc!!