Skeletal System: The Axial Skeleton Skull Vertebral Column Ribs Sternum

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

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

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 Sphenoid Bone: medial base of the skull Connects the frontal, temporal, and parietal bones Sella Turcica: a “saddle” for the pituitary gland in the brain

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

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

Facial Bones Your face grows the most in the first two years; then stops by the age of 16. Nasal Bones Maxillae: 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

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

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)

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

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”)

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 vertebrae that fuse Fusion occurs between 20-30 years of age

Epidural Anesthesia Numbing medicine is delivered near the spinal cord through the sacrum

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

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