Axial Skeleton Anatomy

Introduction

• The adult skeleton has 206 bones.
• The axial skeleton includes 80 bones, providing support and protection for organs in the head, neck, and torso.
• The appendicular skeleton contains 126 bones and forms the upper and lower limbs.
• The axial skeleton is comprised of the skull (cranial and facial bones), the vertebral column, and the thoracic cage.

Selected Bone Markings of the Axial Skeleton

• Foramen are openings and allow passage for blood vessels and nerves.
• Fossa are shallow depressions for muscle attachment or articulation (joints).
• Meatus are tube-like openings that create tubular passageways for blood vessels and nerves.
• Condyle are smooth, rounded articular processes for articulation.

Cranial Bones

• There are 8 cranial bones that surround and protect the organs of hearing, equilibrium and the brain.
• There are 2 parietal bones.
• There are 2 temporal bones.
• There is 1 frontal bone.
• There is 1 occipital bone.
• There is 1 sphenoid bone.
• There is 1 ethmoid bone.

Cranial Sutures

• Cranial sutures are the joints between the cranial bones
• The coronal suture joins the frontal and parietal bones.
• The sagittal suture joins the parietal bones.
• The lambdoid suture joins both parietal bones with the occipital bone.
• The squamous suture joins the parietal and temporal bones.

Facial Bones

• There are 14 facial bones that provide the shape for the face, house the teeth, and provide attachments for the muscles of facial expression.
• There are 2 maxillae.
• There are 2 zygomatic bones.
• There are 2 lacrimal bones.
• There are 2 nasal bones.
• There are 2 inferior nasal conchae.
• There are 2 palatine bones.
• There is 1 mandible.
• There is 1 vomer.

Hard Palate and Nasal Septum

• The hard palate is formed by the fusion of four bones: 2 maxillary bones (3/4) and 2 palatine bones (1/4).
• The nasal septum is formed by bones and cartilage.
• Vomer and the perpendicular plate are the bones in the nasal septum.
• The cartilage is anterior to these two bones.

Hyoid Bone

• The hyoid bone is not attached to the axial skeleton.
• Is located in the anterior neck region.
• It is a U-shaped bone.
• It doe not articulate with any other bones.
• It is secured in place by ligaments and muscles.

Paranasal Sinuses

• Sinuses are cavities lined with mucous membranes.
• They are located near and have openings into the nasal cavities.

Vertebral Column

• Infants have 33 vertebrae, adults have 26.
• The vertebral column has four normal curves: cervical, thoracic, lumbar, and sacral.
• The cervical curve is formed by 7 cervical vertebrae.
• The thoracic curve is formed by 12 thoracic vertebrae.
• The lumbar curve is formed by 5 lumbar vertebrae.
• The sacral curve is formed by 5 fused sacral vertebrae.
• A single primary spinal curve becomes the thoracic and sacral curves in newborns.
• Secondary cervical (head erect) and Lumber (stand) curves develop several months later.
• Each group of vertebra has its own structure, yet the cervical, thoracic, and lumbar vertebrae share 6 common structures: body, transverse process, spinous process, vertebral foramen, superior articular facet, and inferior articular facet.

Sacrum and Coccyx

• The sacrum and coccyx each contains sacral foramina.

Abnormal Spinal Curvatures

• Scoliosis causes lateral bending.
• Kyphosis causes an exaggerated thoracic curve which results in a hunched back and rounded shoulders.
• Lordosis causes an exaggerated lumbar curve which results in swayback and a protruding abdomen.

Thoracic Cage

• The thoracic cage is made up of the sternum, ribs, costal cartilage, and the bodies of the thoracic vertebrae.
• The sternum consists of the manubrium, body of the sternum, and xiphoid process.
• There are 12 pairs of ribs.
• The first 7 pairs are true ribs.
• The last 5 pairs are false ribs.
• Ribs 8-10 are attached to the costal cartilage through the 7th costal cartilage.
• Ribs 11 and 12 are known as floating ribs.
• The space between ribs is called the intercostal space.