Chapter 7: The Axial Skeleton

Human Skeleton Human Skeleton = 206 Bones Axial Skeleton: -longitudinal axis -80 bones Appendicular Skeleton: -limbs -126 bones

The Axial Skeleton Figure 7–1a

Axial Skeleton

Appendicular Skeleton

Axial Skeleton Function Support and protect organs in dorsal and ventral body cavities Provide surface area for muscle attachment: Adjust position of head, neck, & trunk Perform respiratory movements Stabilize appendicular skeleton

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

Skull: 22 Bones

Cranial Bones Enclose the cranial cavity Which contains the brain: and its fluids, blood vessels, nerves, and membranes

The Facial Bones Superficial facial bones: Deep 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 Vomer

The Maxillary Bones The largest facial bones Figure 7–10a

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)

The Palatine Bones Figure 7–10b,c

Functions of the Palatine Bones Form the posterior portion of the hard palate Contribute to the floors of the orbits

The structures and functions of the nasal complex.

The Small Bones of the Face Figure 7–11

Functions of the 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

The Mandible Forms the lower jaw Figure 7–12a,b

The Hyoid Bone Function: Supports the larynx Attaches muscles of the larynx, pharynx, and tongue Figure 7–12c

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

Skull Four major sutures: Lambdoid: Corona: Sagittal: Squamous: - separates occipital bone from parietal bones Corona: - separates frontal bone from parietal bones Sagittal: - separates parietal bones Squamous: - (2) separates temporal bone from parietal bone

Sutures The immovable joints of the skull Figure 7–3a, b

Sutures Figure 7–3c

Sutures Figure 7–3d, e

The Orbital Complex Portions of 7 cranial and facial bones Figure 7–13

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

The Nasal Complex Bones of the nasal cavities and paranasal sinuses Figure 7–14

The Nasal Complex: Sinuses air filled chambers inside flat bones Function: Reduce weight of bone House mucus membranes that moisten and clean incoming air Found in: Sphenoid, ethmoid, frontal, palatine, and maxillary bones

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

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 bones

The Infant Skull Fusion is not complete at birth: Fontanels 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

The 4 Fontanels Anterior fontanel: Occipital fontanel: frontal, sagittal, and coronal sutures Occipital fontanel: lambdoid and sagittal sutures Sphenoidal fontanels: squamous and coronal sutures Mastoid fontanel: squamous and lambdoid sutures

Infant Skull

Skull Development Abnormalities Craniostenosis: Premature closure of frontanels, Without surgery, the brain is crushed Microcephaly: - Brain fails to enlarge - Cranium remains small

Craniostenosis Microcephaly

In which bone is the foramen magnum located? sphenoid occipital bone ethmoid parietal bone

Tomás suffers a blow to the skull that fractures the right superior lateral surface of his cranium. Which bone is fractured? frontal bone right temporal bone right parietal bone ethmoid

Which bone contains the depression called the sella turcica Which bone contains the depression called the sella turcica? What is located in this depression? sphenoid bone; pituitary gland ethmoid; olfactory epithelium temporal bone; inner ear lacrimal bone; tear apparatus

The vertebral regions, the curvatures of the vertebral column, and their functions.

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)

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

The Vertebrae Figure 7–20a

Comparing Vertebrae

Characteristics of the Sacrum and Coccyx 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

4 Curvatures of the Vertebral Column Cervical curve Thoracic curve Lumbar curve Sacral curve

Primary Curves Thoracic and sacral curves: are called primary curves (present during fetal development) or accommodation curves (accommodate internal organs)

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

Abnormalities in Curvature Kyphosis: - exaggerated thoracic curvature Lordosis: - exaggerated lumber curvature Scoliosis: - abnormal lateral curvature

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

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

Structure of a Vertebra Figure 7–17a,b

The Vertebral Canal Figure 7–17d,e

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

Why does the vertebral column of an adult have fewer vertebrae than that of a newborn? Vertebrae are absorbed as adult stature is reached. Newborns require more support in the cervical region. The sacrum and coccyx fuse post-puberty. Vertebrae are formed that later become ribs.

What is the importance of the secondary curves of the spine? balances weight of head balances weight on lower limbs allows walking provides greater flexibility

superior articular processes pedicles transverse processes When you run your finger along a person’s spine, what part of the vertebrae are you feeling just beneath the skin? superior articular processes pedicles transverse processes spinous processes

Joe suffered a hairline fracture at the base of the dens Joe suffered a hairline fracture at the base of the dens. Which bone is fractured, and where is it located? second cervical vertebra; posterior neck first cervical vertebra; posterior neck occipital bone; posterior base of skull sacrum; posterior pelvis

thoracic lumbar sacral cervical 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? thoracic lumbar sacral cervical

Why are the bodies of the lumbar vertebrae so large? They develop first and therefore have longer to grow. To provide more flexibility. To distribute weight over a larger area. To provide greater protection to the lumbar spinal nerves.

The significance of articulations between ribs, thoracic vertebrae, and sternum.

The Thoracic Cage The skeleton of the chest: Consists of: supports the thoracic cavity Consists of: 24 Ribs 1 sternum (breastbone)

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

The Rib Cage Formed of ribs and sternum Figure 7–22a

Articulations of Ribs and Vertebrae Figure 7–22b

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

The Ribs Figure 7–23

Functions of Ribs Ribs: Rib movements (breathing): are flexible are mobile can absorb shock Rib movements (breathing): affect width and depth of thoracic cage changing its volume

Ribs Ribs (costae): Ribs are divided into 3 types: 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

KEY CONCEPT The axial skeleton: Vertebrae: 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

How could you distinguish between true ribs and false ribs? True ribs attach directly to the sternum by their own costal cartilage. True ribs are entirely bony. False ribs are not part of the thoracic cage. True ribs are attached only to the sternum.

Improper administration of cardiopulmonary resuscitation (CPR) can result in a fracture of which bone(s)? cervical vertebra and ribs thoracic vertebra and ribs sternum and thoracic vertebra sternum and ribs

What are the main differences between vertebrosternal and vertebrochondral ribs? Vertebrosternal ribs attach to the sternum. Vertebrochondral ribs attach to costal cartilage. Vertebrosternal ribs increase in curvature and length from 1 - 7. All of the above are true.