Chapter 7:

The Axial Skeleton

1

Human Skeleton

• Human Skeleton = 206 Bones1. Axial Skeleton:

-longitudinal axis-80 bones

2. Appendicular Skeleton:-limbs-126 bones

2

The Axial Skeleton

Figure 7–1a

3

Axial Skeleton

4

Appendicular Skeleton

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Axial Skeleton Function

1. Support and protect organs in dorsal and ventral body cavities

2. Provide surface area for muscle attachment:

A. Adjust position of head, neck, & trunk

B. Perform respiratory movementsC. Stabilize appendicular skeleton

6

Bones of the Axial Skeleton

• The skull: 22 bones– 8 cranial bones:

• form the braincase or cranium

– 14 facial bones:• protect and support entrances to digestive

and respiratory tracts

• Skull bones interconnect at immovable joints called sutures– Dense fibrous CT

7

Skull: 22 Bones

8

Cranial Bones

• Enclose the cranial cavity• Which contains the brain:

– and its fluids, blood vessels, nerves, and membranes

9

The Facial Bones

• Superficial facial bones:– for muscle attachment – Maxillary, Lacrimal, Nasal, Zygomatic,

and Mandible

• Deep facial bones:– separate the oral and nasal cavities– form the nasal septum – Palatine bones, Inferior nasal conchae,

and Vomer10

The Maxillary Bones• The largest facial bones

Figure 7–10a

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Functions of the Maxillary Bones

• Support upper teeth• Form inferior orbital rim• Form lateral margins of external

nares• Form upper jaw and hard palate• Contain maxillary sinuses (largest

sinuses)

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The Palatine Bones

Figure 7–10b,c

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Functions of the Palatine Bones

• Form the posterior portion of the hard palate

• Contribute to the floors of the orbits

14

The structures and functions of the nasal

complex.

15

The Small Bones of the Face

Figure 7–11

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Functions of the Nasal Bones

• Nasal Bones– Support the bridge of the nose – Connect to cartilages of the distal part of the

nose (external nares)

• Vomer– Forms the inferior portion of the bony nasal

septum

• Inferior Nasal Conchae– To create air turbulence in the nasal cavity– To increase the epithelial surface area– To warm and humidify inhaled air 17

The Mandible Forms the lower jaw

Figure 7–12a,b18

The Hyoid Bone

• Function:– Supports the larynx– Attaches muscles of the

larynx, pharynx, and tongue

Figure 7–12c

19

Marks of the Hyoid Bone

• Greater horns (greater cornua):– support larynx– attach muscles of the tongue

• Lesser horns (lesser cornua):– attach stylohyoid ligaments – support hyoid and larynx

20

Skull

• Four major sutures:1. Lambdoid:

- separates occipital bone from parietal bones

2. Corona: - separates frontal bone from parietal bones

3. Sagittal: - separates parietal bones

4. Squamous: - (2) separates temporal bone from parietal bone

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Sutures

• The immovable joints of the skull

Figure 7–3a, b

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Sutures

Figure 7–3c

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Sutures

Figure 7–3d, e

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The Orbital Complex• Portions of 7 cranial and facial

bones

Figure 7–13

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The Orbital Complex

• Forms the eye sockets (orbits):– frontal bone (roof)– maxillary bone (floor)– maxillary, lacrimal and ethmoid bones

(orbital rim and medial wall)– sphenoid and palatine bones

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The Nasal Complex• Bones of the nasal cavities and paranasal

sinuses

Figure 7–14

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The Nasal Complex: Sinuses

• Sinuses: – air filled chambers inside flat bones– Function:

1. Reduce weight of bone2. House mucus membranes that moisten and

clean incoming air

- Found in:- Sphenoid, ethmoid, frontal, palatine, and

maxillary bones

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The differences between the skulls of infants, children, and adults.

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Skull Development

• Intramembranous ossification from many centers of ossification

• During development:– brain grows more rapidly than cranial bones

• Growing skull bones are held together by bands of fibrous CT to provide flexibility– Expansion of brain, compression for birth

• Large intersections of CT between the bones = fontalels (“soft spots”)– Persist until age 5

• Around age 5:– Brain stops growing in size, solid sutures form

between cranial bones30

The Infant Skull

• Fusion is not complete at birth: – 2 frontal bones– 4 occipital bones– several sphenoid and temporal elements

• Fontanels – Are areas of fibrous connective tissue

(soft spots) – Cover unfused sutures in the infant skull – Allow the skull to flex during birth

31

The 4 Fontanels

• Anterior fontanel:– frontal, sagittal, and coronal sutures

• Occipital fontanel:– lambdoid and sagittal sutures

• Sphenoidal fontanels:– squamous and coronal sutures

• Mastoid fontanel:– squamous and lambdoid sutures

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Infant Skull

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Skull Development Abnormalities

1. Craniostenosis:- Premature closure of frontanels,- Without surgery, the brain is

crushed

2. Microcephaly:- Brain fails to enlarge

- Cranium remains small

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Craniostenosis

Microcephaly

35

In which bone is the foramen magnum located?

A. sphenoidB. occipital boneC. ethmoidD. parietal bone

36

Tomás suffers a blow to the skull that fractures the right superior lateral surface of his cranium.

Which bone is fractured?

A. frontal boneB. right temporal boneC. right parietal boneD. ethmoid

37

Which bone contains the depression called the sella

turcica? What is located in this depression?

A. sphenoid bone; pituitary gland

B. ethmoid; olfactory epithelium

C. temporal bone; inner earD. lacrimal bone; tear

apparatus38

The vertebral regions, the curvatures of the

vertebral column, and their functions.

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The Vertebral Column: 26 Bones

• The spine or vertebral column:– protects the spinal cord– supports the head and body

• 7 cervical vertebrae (C1-C7)

• 12 Thoracic vertebrae (T1-T12)

• 5 Lumbar vertebrae (L1-L5)

• 1 Sacrum (5 fused)• 1 Coccyx (3-5 fused)

40

Regions and Curves of the Vertebral Column

• 26 bones: – 24 vertebrae, the

sacrum, and coccyx

• Vertebral column is not straight– 4 curves bring the

weight of the body in line with the central axis

Figure 7–16

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The Vertebrae

Figure 7–20a

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Comparing Vertebrae

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Characteristics of the Sacrum and Coccyx

• The sacrum:– is curved, more in males than in

females– protects reproductive, urinary, and

digestive organs

• The coccyx:– attaches ligaments and a constricting

muscle of the anus

44

4 Curvatures of the Vertebral Column

1. Cervical curve2. Thoracic curve3. Lumbar curve4. Sacral curve

45

Primary Curves

• Thoracic and sacral curves:– are called primary curves (present

during fetal development)– or accommodation curves

(accommodate internal organs)

46

Secondary Curves

• Lumbar and cervical curves:– are called secondary curves (appear

after birth in first year of life)– or compensation curves (shift body

weight for upright posture)– Necessary for bipedalism– Cervical: holds head up– Lumbar: standing

47

Abnormalities in Curvature1. Kyphosis:

- exaggerated thoracic curvature

2. Lordosis: - exaggerated lumber curvature

3. Scoliosis: - abnormal lateral curvature

48

Construction of Column

• Vertebral body: stacking– transfers weight along the

spine

• Intervertebral disc:– Spacing between bodies (not

C1 and C2)– Annulus Fibrosus: Outside

• Fibrocartilage

– Nucleus pulposus: Inside• Gel (cushion)• Absorbs Shock

– Loss of water from discs = shrinking height

49

Construction of Column

• Elastic ligaments: – link bodies for alignment

• Intervertebral foramen: – holes formed by spacing from discs, allow spinal

nerves to exit column• Vertebral arch:

– Bone attached to vertebral body, with body it forms vertebral foramen

• Vertebral Foramen:– Hole for spinal cord

• Vertebral Canal:– Bony canal for spinal cord– Formed by stacking of vertebral foramen

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Structure of a Vertebra

Figure 7–17a,b

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The Vertebral Canal

Figure 7–17d,e52

Spina bifida

• Vertebral arch fails to develop correctly at 3 weeks (fetus) and the spinal cord is unprotected or even exposed

• 4/1000 births show some degree– Due to lack of folic acid

53

Why does the vertebral column of an adult have fewer

vertebrae than that of a newborn?

A. Vertebrae are absorbed as adult stature is reached.

B. Newborns require more support in the cervical region.

C. The sacrum and coccyx fuse post-puberty.

D. Vertebrae are formed that later become ribs. 54

What is the importance of the secondary curves of the spine?

A. balances weight of headB. balances weight on lower

limbsC. allows walkingD. provides greater

flexibility

55

When you run your finger along a person’s spine, what part of the vertebrae are you feeling just

beneath the skin?

A. superior articular processes

B. pediclesC. transverse processesD. spinous processes

56

Joe suffered a hairline fracture at the base of the dens. Which bone is fractured, and where is

it located?

A. second cervical vertebra; posterior neck

B. first cervical vertebra; posterior neck

C. occipital bone; posterior base of skull

D. sacrum; posterior pelvis57

Examining a human vertebra, you notice that, in addition to the large foramen for the spinal

cord, two smaller foramina are on either side of the bone in the region of the transverse

processes. From which region of the vertebral column is this vertebra?

A. thoracicB. lumbarC. sacralD. cervical

58

Why are the bodies of the lumbar vertebrae so large?

A. They develop first and therefore have longer to grow.

B. To provide more flexibility.C. To distribute weight over a

larger area.D. To provide greater

protection to the lumbar spinal nerves.

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The significance of articulations between

ribs, thoracic vertebrae, and sternum.

60

The Thoracic Cage

• The skeleton of the chest:– supports the thoracic cavity

• Consists of:– 24 Ribs – 1 sternum (breastbone)

61

The Sternum

• The sternum:– a flat bone– in the midline of the thoracic wall

62

The Rib Cage

• Formed of ribs and sternum

Figure 7–22a

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Articulations of Ribs and Vertebrae

Figure 7–22b64

Functions of the Thoracic Cage

• Protects organs of the thoracic cavity:– heart, lungs, and thymus

• Attaches muscles:– for respiration– of the vertebral column– of the pectoral girdle– of the upper limbs

65

The Ribs

Figure 7–23

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Functions of Ribs

• Ribs:– are flexible– are mobile– can absorb shock

• Rib movements (breathing):– affect width and depth of thoracic

cage– changing its volume

67

Ribs• Ribs (costae):

– are 12 pairs of long, curved, flat bones– extending from the thoracic vertebrae

• Ribs are divided into 3 types:1. 7 pairs of true ribs:

• Separate cartilage to attach to sternum

2. 3 pairs of false ribs:• Common shared cartilage to attach to sternum

3. 2 pairs of floating ribs: - no cartilage, no attachment to sternum

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KEY CONCEPT

• The axial skeleton:– protects the brain, spinal cord, and

visceral organs of the chest• Vertebrae:

– conduct body weight to the lower limbs

• Lower vertebrae are larger and stronger:– because they bear more weight

69

How could you distinguish between true ribs and false

ribs?

A. True ribs attach directly to the sternum by their own costal cartilage.

B. True ribs are entirely bony.C. False ribs are not part of the

thoracic cage.D. True ribs are attached only

to the sternum. 70

Improper administration of cardiopulmonary resuscitation (CPR) can result in a fracture of

which bone(s)?

A. cervical vertebra and ribsB. thoracic vertebra and ribsC. sternum and thoracic

vertebraD. sternum and ribs

71

What are the main differences between vertebrosternal and

vertebrochondral ribs?

A. Vertebrosternal ribs attach to the sternum.

B. Vertebrochondral ribs attach to costal cartilage.

C. Vertebrosternal ribs increase in curvature and length from 1 - 7.

D. All of the above are true.72