The Axial Skeleton

Functions of the Axial Skeleton • Supports and protects organs in body cavities • Attaches to muscles of: – head, neck, and trunk – respiration – appendicular skeleton

Figure 7–1a

The Axial Skeleton

The Skull

Figure 7–1b

Figure 7–2

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Sinuses • Cavities which decrease the weight of the skull: – lined with mucus membranes – protect the entrances of the respiratory system

The 4 Major Sutures 1. 2. 3. 4.

Lambdoid suture Coronal suture Sagittal suture Squamous suture

The Cranial Bones • • • • • •

Occipital bone Frontal bone Sphenoid Ethmoid Parietal bones Temporal bones

The Occipital Bone •External occipital protuberance •Occipital condyles: –articulate with neck •Inferior and superior nuchal lines: –to attach ligaments •Foramen magnum: –connects cranial and spinal cavities •Jugular foramen: –for jugular vein

Figure 7–5a

2

The Temporal Bones

The Parietal Bones

•Mastoid process: –for muscle attachment •Styloid process: –to attach tendons and ligaments of the hyoid, tongue and pharynx

•Carotid canal: –for internal carotid artery •Foramen lacerum: –for carotid and small arteries –External acoustic canal: –ends at tympanic membrane •Stylomastoid foramen: –for facial nerve •Internal acoustic canal: –for blood vessels and nerves of the inner ear

Figure 7–5b

The Frontal Bone

Figure 7–7

The Sphenoid •Sella turcica: –saddle-shaped enclosure –on the superior surface of the body –Lesser wings: –anterior to the sella turcica •Greater wings: –form part of the cranial floor –sphenoidal spine –posterior wall of the orbit •Optic canals: –for optic nerves •Foramen rotundum: –for blood vessels and nerves of the face •Foramen ovale: –for blood vessels and nerves of the face •Foramen spinosum: –for blood vessels and nerves of the jaws Figure 7–6

Figure 7–8

3

The Ethmoid

The Palatine Bones

The cribriform plate contains the crista galli Figure 7–9

The Maxillary Bones

Figure 7–10b,c

The Small Bones of the Face

• The largest facial bones

Figure 7–10a

Figure 7–11

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The Mandible

The Orbital Complex

–frontal bone (roof) –maxillary bone (floor) –maxillary, lacrimal and ethmoid bones (orbital rim and medial wall) –sphenoid and palatine bones Figure 7–12a,b

Figure 7–13

The Nasal Complex

The Hyoid Bone

• • •

Figure 7–12c

Frontal bone, sphenoid, and ethmoid: – superior wall of nasal cavities Maxillary, lacrimal, ethmoid, and inferior nasal conchae: – lateral walls of nasal cavities Maxillary and nasal bones: – bridge of nose

Figure 7–14

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Fontanels • Are areas of fibrous connective tissue (soft spots) • Cover unfused sutures in the infant skull • Allow the skull to flex during birth

Vertebrae of the Vertebral Column • The neck: – 7 cervical vertebrae

• The upper back: – 12 thoracic vertebrae – each articulate with one or more pairs of ribs

• The lower back: – 5 lumbar vertebrae

Regions and Curves of the Vertebral Column

Curves

• 26 bones: – 24 vertebrae, the sacrum, and coccyx

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

• Thoracic and sacral curves: – are called primary curves (present during fetal development) – or accommodation curves (accommodate internal organs) • Lumbar and cervical curves: – are called secondary curves (appear after birth) – or compensation curves (shift body weight for upright posture)

Figure 7–16

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Structure of a Vertebra

The Vertebral Canal

•Superior articular process •Inferior articular process •Intervertebral foraminae: –gaps between pedicles of adjacent vertebrae –for nerve connections to spinal cord •Vertebral canal: –formed by vertebral foraminae –encloses the spinal cord

•The vertebral body (centrum): –transfers weight along the spine •The vertebral arch: –posterior margin of vertebral foramen •The articular processes: –lateral projections between laminae and pedicles

Figure 7–17d,e

Figure 7–17a,b

The Vertebral Arch

Vertebral Regions

•Pedicles: –walls of the vertebral arch •Laminae: –roof of the vertebral arch •Spinous process: –projection where vertebral laminae fuse •Transverse process: –projection where laminae join pedicles

Figure 7–17c

Figure 7–16

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Characteristics of Cervical Vertebrae

The Cervical Vertebrae

• Vertebra prominens (C7): – transitions to thoracic vertebrae – has a long spinous process with a broad tubercle – has large transverse processes

• Ligamentum nuchae (elastic ligament) extends from C7 to skull –small body (support only head) –large vertebral foramen (largest part of spinal cord) •C1 (atlas) has no spinous process •All others have short spinous processes •Tip of each spinous process is notched (bifid)

Figure7–18a, b

The Cervical Vertebrae

The Thoracic Vertebrae

•Atlas (C1): •Axis (C2): –articulates with occiptal condyles of skull –supports the atlas –has no body or spinous process –has heavy spinous process –has a large, round foramen –to attach muscles of head and neck •dens Figure7–18c, d

•Thoracic vertebrae (T1–T12): –have heart-shaped bodies –larger bodies than in C1–C7 –smaller vertebral foramen than in C1–C7 –long, slender spinous processes –which articulate with heads of ribs

Figure 7–19b, c

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The Lumbar Vertebrae

The Sacrum and Coccyx

–largest vertebrae –oval-shaped bodies –triangular vertebral foramen

consists of 5 fused sacral vertebrae •Sacral canal: –replaces the vertebral canal

is curved, more in males than in females

Figure 7–20b, c

•Attaches: –the axial skeleton to pelvic girdle of appendicular skeleton –broad muscles that move the thigh

Figure 7–21

Characteristics of the Coccyx

Comparing Vertebrae

• The coccyx: – attaches ligaments and a constricting muscle of the anus

• Mature coccyx: – consists of 3 to 5 fused coccygeal vertebrae

Table 7–2

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The Rib Cage

The Ribs •Ribs –are 12 pairs of long, curved, flat bones –extending from the thoracic vertebrae •Ribs are divided into 2 types: –true ribs –false ribs

• Formed of ribs and sternum

Figure 7–22a

Articulations of Ribs and Vertebrae

Figure 7–23

Structures of the Ribs •

•

•

•

The head (capitulum): – at the vertebral end of the rib – has superior and inferior articular facets The neck: – the short area between the head and the tubercle The tubercle (tuberculum): – a small dorsal elevation – has an auricular facet that contacts the facet of its thoracic vertebra (at T1–T10 only) The tubercular body (shaft): – attaches muscles of the pectoral girdle and trunk – attaches to the intercostal muscles which move the ribs

Figure 7–22b

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3 Parts of the Sternum 1. The manubrium – – –

articulates with collarbones (clavicles) articulates with cartilages of 1st rib pair has a jugular notch between clavicular articulations

2. The sternal body – – –

is tongue-shaped attaches to the manubrium attaches to costal cartilages of ribs 2–7

3. The xiphoid process attaches to diaphragm and rectus abdominis muscles

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

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