7 The Axial Skeleton

Repition…. Repition…. Repition…. Repition…. Repition….

I. The Skeleton A. Bones, cartilage, joints, and ligaments 1. joints - also called articulations B. 206 named bones grouped into two divisions 1. Axial skeleton (80 bones) ► skull, vertebral column, and thoracic cage 2. Appendicular skeleton (126 bones) ► upper and lower limbs

II. The Cranium (Skull) A. The cranium is formed by cranial and facial bones 1. enclose and protect the brain 2. provide attachment sites for muscles of the head and neck B. Facial bones 1. Form framework of the face 2. Form cavities for sense organs of sight, taste, and smell 3. Provide openings for passage of air and food 4. Hold the teeth in place 5. Anchor muscles of the face

C. Internally bony ridges divide skull into distinct fossae (surfaces) 1. anterior 2. middle 3. posterior D. Brain sits within the cranial fossae 1.brain occupies cranial cavity

Anterior cranial fossa Middle cranial fossa Posterior cranial fossa Superior view of the cranial fossae 7

E. The skull contains smaller cavities 1. middle & inner ear cavities—in lateral aspect of cranial base 2. nasal cavity—lies in and posterior to the nose 3. orbits—house the eyeballs 4. sinuses — air-filled spaces in bones around the nasal cavity

Sinuses of the cranium 9

F. The skull contains approximately 85 named openings 1. foramina, canals, and fissures 2. provide openings for important structures a. spinal cord b. blood vessels serving the brain c. 12 pairs of cranial nerves

IV. Cranial Bones A. Formed from eight large bones 1. paired bones a. temporal bones b. parietal bones 2. unpaired bones a. frontal bone b. occipital bone c. sphenoid bone d. ethmoid bone

V. Sutures A. Four sutures of the cranium 1. coronal suture - runs in the coronal plane 2. squamous suture - parietal bone meets temporal bone 3. sagittal suture - where right and left parietal bones 4. lambdoid suture – parietal bones meet the occipital bone

Cranium

right side of the skull Coronal suture Frontal bone Sphenoid bone Parietal bone Sphenoid bone Squamous suture Ethmoid bone Lambdoid suture Lacrimal bone Lacrimal fossa Occipital bone Nasal bone Temporal bone Zygomatic process Zygomatic bone Maxilla External acoustic meatus Mastoid process Styloid process Mandible Condylar process Mental foramen Mandibular notch Mandibular ramus Coronoid process Mandibular angle 14

right side of the skull 15

Superior orbital fissure Frontal bone Parietal bone Supraorbital foramen Nasal bone Sphenoid bone Superior orbital fissure Temporal bone Optic canal Ethmoid bone Inferior orbital fissure Lacrimal bone Ethmoid bone Zygomatic bone Infraorbital foramen Maxilla Vomer Mandible Mental foramen 16

Ethmoid bone 17

External occipital protuberance Parietal bone Sagittal suture Lambdoid suture Occipital bone Superior nuchal line External occipital protuberance Inferior nuchal line Occipital condyle 18

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Maxilla Hard palate Palatine bone Infraorbital foramen Maxilla Zygomatic bone Sphenoid bone Vomer zygomatic process External acoustic meatus Styloid process Mastoid process Temporal bone Jugular foramen Occipital condyle Occipital bone External occipital protuberance Foramen magnum Inferior view of the skull (mandible removed) 20

Inferior view of the skull (mandible removed) 21

External acoustic meatus Zygomatic process Mastoid process Styloid process 22

Optic canal Lesser wing Foramen rotundum Greater wing Foramen ovale Sella turcica Foramen spinosum Body of sphenoid Superior view 23

Cribriform plate with cribriform foramina Crista galli Cribriform plate with cribriform foramina 24

The Holes in the Head Optic foramen Foramen rotundum Foramen ovale Foramen spinosum Foramen lacerum Internal acoustic meatus Jugular foramen Hypoglossal canal Foramen magnum ▲

Internal acoustic meatus Crista galli View Ethmoid bone Cribriform plate Frontal bone Lesser wing Optic canal Sphenoid Greater wing Foramen rotundum sella turcica Foramen ovale Foramen spinosum Foramen lacerum Temporal bone Internal acoustic meatus Jugular foramen Hypoglossal canal Parietal bone Occipital bone Foramen magnum Superior view of the skull, calvaria removed 26

Superior view of the skull, calvaria removed 27

The Sphenoid Bone Optic canal Lesser wing Foramen rotundum Greater wing Foramen ovale Sella turcica Foramen spinosum Body of sphenoid Superior view 28

29 Parietal bone Coronal suture Frontal bone Sphenoid bone Squamous suture Temporal bone Crista galli Lambdoid suture Nasal bone Occipital bone Ethmoid bone Vomer External occipital protuberance Maxilla Internal acoustic meatus Mandible Mandibular foramen Palatine bone Midsagittal section showing the internal anatomy of the left half of skull 29

Midsagittal section showing the internal anatomy of the left half of skull 30

Mandible Temporomandibular joint Coronoid process Mandibular notch Condylar process Mandibular foramen Ramus of mandible Mental foramen Mandibular angle Body of mandible Mandible, right lateral view 31

Mandible Mandible, right lateral view 32

Figure 7-15a Paranasal sinuses. Frontal sinus Ethmoidal air cells (sinus) Sphenoidal sinus Maxillary sinus Anterior aspect 33

Hyoid Bone

Figure 7.17 The hyoid bone. Greater horn Lesser horn Body 35

XIII. Thoracic Cage 36 Jugular notch Clavicular notch Manubrium Sternal angle Body Sternum True ribs (17) Xiphoid process False ribs (812) Costal cartilage L1 Vertebra Floating ribs (11, 12) 36

XIII. Thoracic Cage L1 Vertebra 37

Vertebral Column

The Vertebral Column A. In the adult, is formed from 26 bones B. Transmits weight of trunk to the lower limbs C. Surrounds and protects the spinal cord 39

Regions and Normal Curvatures A. The vertebral column has five major regions ► 7 cervical vertebrae of the neck region ► 12 thoracic vertebrae ► 5 lumbar vertebrae ► Sacrum - five fused bones ► Coccyx - inferior to sacrum 40

41 C1 Cervical curvature (concave) 7 vertebrae, C1  C7 2 3 Cervical curvature (concave) 4 7 vertebrae, C1  C7 5 6 7 T1 Spinous process 2 3 Transverse processes 4 5 Thoracic curvature 6 (convex) 12 vertebrae, T1  T12 7 8 9 Intervertebral discs 10 11 Intervertebral foramen 12 L1 2 Lumbar curvature 3 (concave) 5 vertebrae, L1  L5 4 5 Sacral curvature (convex) 5 fused vertebrae sacrum Coccyx 4 fused vertebrae Anterior view Right lateral view 41

Regions and Normal Curvatures A. Curvatures of the spine 1. Cervical and lumbar curvatures ► Concave posteriorly 2. Thoracic and sacral curvatures ► Convex posteriority kyphosis – exagerated curvature in thoracic region (humpback) lordosis – exaggerated curvature in the lumbar region scoliosis – S-shaped curvature of the whole vertebral column 42

Supraspinous ligament Anterior longitudinal ligament Intervertebral disc Supraspinous ligament Anterior longitudinal ligament Transverse process Sectioned spinous process Intervertebral foramen Posterior longitudinal ligament Ligamentum flavum Anulus fibrosus Interspinous ligament Nucleus pulposus Inferior articular process Sectioned body of vertebra Median section of three vertebrae, illustrating the composition of the discs and the ligaments 43

Posterior longitudinal ligament Anterior longitudinal ligament Body of a vertebra Intervertebral disc Anterior view of part of the spinal column 44

Intervertebral Discs A. Are cushion-like pads between vertebrae 1. Nucleus pulposus a. gelatinous inner sphere b. absorbs compressive stresses 2. Anulus fibrosus a. outer rings formed of ligament b. inner rings formed of fibrocartilage c. contains the nucleus pulposus 45

Vertebrae

Superior articular process and facet Posterior Vertebral arch Lamina Spinous process Transverse process Superior articular process and facet Vertebral foramen Pedicle Body Anterior 47

Posterior Anterior 48

Cervical Vertebrae A. Cervical 1. C1 (atlas) no body, no spine 2. C2 (axis) bifid spine, dens (head) 3. C3-6 bifid spine 4. C7 non-bifid spine, first bulge in lower neck 5. transverse foramen (vessel+nerve) 6. bodies get larger in descending fashion 49

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Transverse ligament of atlas Dens of axis Transverse ligament of atlas C1 (atlas) C2 (axis) C3 Inferior articular process Bifid spinous process Transverse processes C7 (vertebra prominens) Cervical vertebrae 51

C1 – The Atlas C1 Posterior Posterior tubercle Posterior arch Transverse foramen Lateral masses Superior articular facet Anterior arch Anterior tubercle Superior view of atlas (C1) 52

C1 – Axis Posterior C2 Spinous process Inferior articular process Lamina Pedicle Superior articular facet Transverse process Dens Body Superior view of axis (C2) 53

Thoracic Vertebrae A. Thoracic 1. long, inferior-directed spinous processes 2. transverse processes are long and heavy 3. T1 superior whole facet : inferior demifacet 4. T2-8 two demifacets; superior large / inferior small 5. T9 single superior demifacet 6. T10-12 whole facet for individual rib articulation 54

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Lumbar Vertebrae A. Lumbar 1. all have largest, thickest bodies 2. spinous processes are oblong and heavy 56

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Superior articular process Body Transverse process Intervertebral disc Inferior articular process Spinous process Lumbar vertebrae 58

The Sacrum

Sacral promontory Body Sacral canal Facet of superior articular process Ala Body of first sacral vertebra Auricular surface Median sacral crest Lateral sacral crest Transverse ridges (sites of vertebral fusion) Posterior sacral foramina Anterior sacral foramina Apex Sacral hiatus Coccyx Coccyx Anterior view Posterior view 60

Coccyx A. Is the “tailbone” B. Formed from 3–5 fused vertebrae C. Offers only slight support to pelvic organs 61

The Thoracic Cage A. Forms the bony framework of the chest B. Components 1. thoracic vertebrae—posteriorly 2. ribs - laterally 3. sternum and costal cartilage - anteriorly C. Protects thoracic organs D. Supports shoulder girdle and upper limbs E. Provides attachment sites for many muscles of the back

Ribs A. All ribs attach to vertebral column posteriorly 1. true ribs—superior seven pairs of ribs ► Attach to sternum by costal cartilage 2. false ribs—inferior five pairs of ribs 3. floating ribs – ribs 11 and 12

64 Jugular notch Clavicular notch Manubrium Sternal angle Body Sternum Xiphisternal joint True ribs (17) Xiphoid process False ribs (812) Intercostal spaces Costal cartilage L1 Vertebra Floating ribs (11, 12) Costal margin Skeleton of the thoracic cage, anterior view 64

Superior costal facet (for head of rib) Angle of rib Body of vertebra Head of rib Intervertebral disc Neck of rib Tubercle of rib Shaft Sternum Cross- section of rib Costal cartilage Vertebral and sternal articulations of a typical true rib 65

Articular facet on tubercle of rib Spinous process Figure 7.25c Ribs. Articular facet on tubercle of rib Spinous process Shaft Transverse costal facet (for tubercle of rib) Ligaments Neck of rib Body of thoracic vertebra Head of rib Superior view of the articulation between a rib and a thoracic vertebra 66

Sternum A. Formed from three sections 1. Manubrium—superior section ► clavicular notches articulate with medial end of clavicles 2. Body—bulk of sternum ► sides are notched at joints for costal cartilage of ribs 2–7 3. Xiphoid process—inferior end of sternum ► ossifies around age 40

68 Jugular notch Clavicular notch Manubrium Body Sternum True ribs (17) Xiphoid process False ribs (812) Intercostal spaces Costal cartilage L1 Vertebra Floating ribs (11, 12) Costal margin Skeleton of the thoracic cage, anterior view 68

Fetal Skeleton A. Fontanelles 1. unossified remnants of membranes 2. soft spots in infant cranium

Fontanelles Frontal suture Frontal bone Anterior fontanelle Ossification center Parietal bone Posterior fontanelle Occipital bone Superior view 70

Infant Cranium Frontal bone Parietal bone Sphenoidal fontanelle Ossification center Posterior fontanelle Mastoid fontanelle Temporal bone (squamous part) Occipital bone Lateral view 71