The Skeletal System: The Axial Skeleton Chapter Seven The Skeletal System: The Axial Skeleton

Introduction Familiarity with the names, shapes, and positions of individual bones helps to locate other organs and to understand how muscles produce different movements due to attachment on individual bones and the use of leverage with joints. The bones, muscles, and joints together form the musculoskeletal system.

Division of the Skeleton Adult has 206 named bones. Most are in pairs (one right, one left). Infants and children have more, because some of them fuse later together) Axial skeleton: Consists of bones along the axis of the body Consists of 80 bones: skull, hyoid bone, bertebral column, sternum, and ribs Appendicular skeleton Consists of 126 bones (arms and legs) Attached to the axial skeleton

Types of Bones Bones are classified according to their shape: long bones, short bones, flat bones, irregular bones, sesamoid bones (shaped like a sesame seed)

1. Skull Consists of 22 bones Located on superior end of the vertebral column. Includes two sets of bones: 8 cranial bones (brain case) = encloses + protects the brain 14 facial bones (form the face) Consists of 22 bones Located on superior end of the vertebral column. Includes two sets of bones: 8 cranial bones (brain case) = encloses + protects the brain Frontal bone, two parietal bones, two temporal bones, occipital bone, sphenoid bone, and the ethmoid bone. 14 facial bones (form the face) Two nasal bones, two maxillae, two zygomatic bones, mandible, two lacrimal bones, two palatine bones, two inferior nasal conchae, and the vomer

Two frontal bones Two parietal bones Two temporal bones The occipital bone The sphenoid bone The ethmoid bones Facial: Two nasal bones Form part of the bridge for the nose Two maxillae Form the upper jawbone Two zygomatic bones Form the cheekbones The mandible Is the jawbone – the largest and strongest facial bone and the only movebale skull bone Two lacrimal bones (inside the eye) Form part of the wall inside the eye socket. Is the smallest bone of the face Two palatine bones (see figure 7.7. Underneath the teeth (light purple)

Two inferior nasal conchae (see figure 7.3, above vomer) Form inside wall of nasal cavity Vomer (see figure 7.3, middle of the nose Now if you look closer at this picture you realize what the frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal and ethmoid bones do? They form the orbit (eye socket) Look at Fig. 7.12

Unique Features of the Skull Sutures Immovable joints that hold the parietal bones and the occipital bone together (7.6) (7.4) squamous suture lambdoid suture coronal suture

Unique Features of the Skull Paranasal Sinuses Spaces in the frontal, sphenoid, ethmoid and maxillary bones that connect nasal cavity

Unique Features of the Skull Fontanels Cartilage and connective tissue Close up Babies heads consists mainly of cartilage and connective tissue. Later ossification occurs and bone replaces the cartilage. Fontanels are fibrous connective tissue between the cranial bones. They are flexible (they must be, in order to be pushed through the birth canal. Allow rapid growth of the brain during infancy. anterior fontanel: closes 18-24 months posterior fontanel: closes around 2 months anterolateral fontanels: closes around 3 month posterolateral fontanel: start closing around 1,2 months, finished by 12 months.

Hyoid Bone Is not in contact with any of the other skull bones Supports the tongue by attachment to muscles of the tongue, neck and pharynx.

2. Vertebral Column The vertebral column, along with the sternum and ribs make up the trunk of the skeleton 4 vertebral curves, 26 bones are divided into 5 regions: Cervical Thoracic Lumbar Sacrum Coccyx The vertebral column, along with the sternum and ribs make up the trunk of the skeleton 4 vertebral curves, 26 bones are divided into 5 regions: Cervical : the neck Thoracic : chest Lumbar : lower back Sacrum : 5 fused vertebrae Coccyx : (KOK-siks) = means cuckoo (looks like the bill of a cockoo) 4 fused vertebrae Check out the hand-out VAHA page 73

Cervical Region There are 7 cervical vertebrae The first is called atlas = supports the skull The second is called axis = permits side to side rotation of the head 3 – 6 = go along with the body movement 7 a bit different (vertebra prominens)

Thoracic Region 12 thoracic vertebrae Must larger and stronger than the cervical vertebrae. Connection with the ribs. 3 basic features: Body – bears weight and increases in size as one moves down the vertebral column Vertebral ach – Articular processes (2) to join the vertebra together Page 77 VAHA

Lumbar Region The largest and strongest – supports large amount of body weight. 5 vertebrae VAHA page 79

Sacrum and Coccyx Sacrum (5 sacral vertebrae) strong foundation for the pelvic girdle Coccyx (COC-siks) formed by the fusion of 4 vertebrae. Used during labor If broken – paralyses from hip down

3. Thorax The entire chest: Collar bone (cavicle) Sternum Breastbone: flat narrow bone of about 6 inches. Connected to ribs by costal cartilage. Ribs 12 pair of ribs. First 7 are true ribs, 5 false ribs (last 2= floating ribs)

3. Thorax False ribs Floating ribs Costal cartilages Do not directly connect to the sternum via costal cartilage Floating ribs Last 2 ribs (11, 12) do not attach at all Costal cartilages Now according to the Bible God created Eve out of a rib of Adams. So Adam has only 11 pair of ribs. Which means that men have one rib pair less than women. Is this a true statement?

Disorders: Homeostatic Imbalances Herniated Disc (slipped disc) Often happens in lumbar region (most weight and stress) nucleus pulposus may herniate (protrude) causing pain and nerve damage Spina Bifida A defect in which part of one or more vertebrae fail to develop completely.