Skeletal System: The Axial Skeleton

1. Skeletal System:The Axial Skeleton SkullVertebral Column Ribs Sternum

2. The Skull • 22 separate bones, many fused together • Two divisions: • Cranial Bones (8 bones) • Facial Bones (14 bones)

3. Ethmoidbone Bones of the Cranium • Enclose and protect the brain • Bones: • Frontal (1) • Parietal (2) • Temporal (2) • Occipital (1) • Sphenoid (1) • Ethmoid (1) Sphenoid bone

4. Ethmoid and Sphenoid Bones • Ethmoid Bone: anterior part of the cranium base • Forms the floor of the cranium • Makes up the medial wall of the orbits (eye sockets) • The major supporting structure for the nasal cavity and attachment for the covering membranes of the brain. • Sphenoid Bone: medial base of the skull • Connects the frontal, temporal, parietal and occipitial bones • SellaTurcica: a “saddle” for the pituitary gland in the brain

5. Sutures in the Skull • Suture: An immovable joint found only in the skull bones • Coronal Suture: between the frontal and two parietals • Sagittal Suture: between the two parietals • Lambdoid Suture: between the two parietals and the occipital • Squamous Sutures: between the parietals and temporal bones

6. Fontanels • Membrane-filled spaces found between cranium bones in infants • “Soft Spots” • Eventually become ossified (replaced by bone- 2 years) • Allow for: • The babies skull to compress, thus allowing childbirth • The brain to grow before the skull is completely fused

7. Facial Bones • Your face grows the most in the first two years; then stops by the age of 16. • Nasal Bones • Maxilla: form the lower orbit and upper jaw • Zygomatic Bones: cheekbones • Mandible: lower jawbone • Lacrimal Bones: smallest bones in the face; have a foramen for the tear duct to pass • Palatine Bones: form the hard palate in the roof of the mouth

8. Hyoid Bone • A U-shaped bone located in the neck between the mandible and the larynx (voicebox) • Does not articulate with any other bone • Supports the tongue • Provides attachment for muscles to allow for neck movement and swallowing

9. Vertebral Column • Protects the Spinal Cord • Allows the major nerves to enter and exit the spinal cord • Usually 33 Bones • 7 Cervical • 12 Thoracic • 5 Lumbar • 5 Sacral (fused to form the sacrum) • 4 Coccygeal (fuse to form one or two fused = coccyx)

10. Typical Vertebra • Body: the thick weight bearing portion • Vertebral foramen: the hole that holds the spinal cord • Spinous Process: a single projection for muscle attachment • Transverse Process: two lateral projections for muscle attachment • Articular Processes: the facets that allow the vertebrae to move with the vertebrae superior and inferior to them

11. Atlas and Axis • Atlas (C1): supports the head • Articulates with the occipital condyles of the skull (nod your head “yes”) • Axis (C2): The “peglike” dens makes a pivot for the head to rotate (move your head “no”)

12. Sacrum and Coccyx • Sacrum (holy bone): 5 fused vertebrae • Usually starts to fuse at age 16-18 and end in mid 20s) • Provides a foundation for the pelvis and allows nerves to pass • Coccyx: Usually 4 (can be 3-5) vertebrae that fuse • Fusion occurs between 20-30 years of age

13. Epidural Anesthesia Numbing medicine is delivered near the spinal cordthrough the sacrum

14. Sternum • Aka: Breastbone • Three separate bones: • Manubrium • Body • Xiphoid Process • Articulates with the ribs, provides attachment point for some abdominal muscles, hematopoiesis • Fuses in late teens; completely by age 40.

15. Ribs • 12 pairs (24 total) • True Ribs: pairs 1-7 directly attach to the sternum by costal cartilage • False Ribs: pairs 8-12, their cartilage attaches to the 7th rib cartilage • Floating Ribs: pairs 11-12; don’t attach to the sternum