The Axial Skeleton. Functions of the Axial Skeleton. The Axial Skeleton. The Skull

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1 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 1

2 Sinuses Cavities which decrease the weight of the skull: lined with mucus membranes protect the entrances of the respiratory system Occipital bone Frontal bone Sphenoid Ethmoid Parietal bones Temporal bones The Cranial Bones The 4 Major Sutures 1. Lambdoid suture 2. Coronal suture 3. Sagittal suture 4. Squamous suture 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

3 The Parietal Bones The Temporal 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 Figure 7 7 The Frontal Bone 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 The Sphenoid Figure 7 6 Figure 7 8 3

4 The Ethmoid The Palatine Bones The cribriform plate contains the crista galli Figure 7 9 Figure 7 10b,c The Maxillary Bones The largest facial bones The Small Bones of the Face Figure 7 10a Figure

5 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 Hyoid Bone The Nasal Complex 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 12c Figure

6 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 26 bones: 24 vertebrae, the sacrum, and coccyx The spine or vertebral column: protects the spinal cord supports the head and body Curves 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 Structure of a Vertebra The Vertebral Canal 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 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 Figure 7 17a,b Figure 7 17d,e 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 The Vertebral Arch Vertebral Regions Figure 7 17c Figure

8 The Cervical Vertebrae small body (support only head) large vertebral foramen (largest part of spinal cord) C 1 (atlas) has no spinous process All others have short spinous processes Tip of each spinous process is notched (bifid) Figure7 18a, b Characteristics of Cervical Vertebrae Vertebra prominens (C 7 ): transitions to thoracic vertebrae has a long spinous process with a broad tubercle has large transverse processes Ligamentum nuchae (elastic ligament) extends from C 7 to skull The Cervical Vertebrae The Thoracic Vertebrae Atlas (C 1 ): Axis (C 2 ): 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 (T 1 T 12 ): have heart-shaped bodies larger bodies than in C 1 C 7 smaller vertebral foramen than in C 1 C 7 long, slender spinous processes which articulate with heads of ribs Figure 7 19b, c 8

9 The Lumbar Vertebrae The Sacrum and Coccyx largest vertebrae oval-shaped bodies triangular vertebral foramen Figure 7 20b, c consists of 5 fused sacral vertebrae Sacral canal: replaces the vertebral canal is curved, more in males than in females Attaches: the axial skeleton to pelvic girdle of appendicular skeleton broad muscles that move the thigh Figure 7 21 Comparing Vertebrae Characteristics of the Coccyx The coccyx: attaches ligaments and a constricting muscle of the anus Mature coccyx: consists of 3 to 5 fused coccygeal vertebrae Table 7 2 9

10 The Rib Cage Formed of ribs and sternum 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 Figure 7 22a Figure 7 23 Articulations of Ribs and Vertebrae 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 T 1 T 10 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 10

11 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 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 11