Axial Skeleton

The axial skeleton forms the central axis of the human body and includes the skull, vertebral column, and thoracic cage. It provides support, protection for vital organs, and attachment points for muscles.

Skull

The skull is a complex structure composed of cranial and facial bones. It protects the brain and forms the structure of the face.

Cranial Bones

• Frontal Bone: Shell-shaped bone forming the anterior cranium and the superior orbits.

• Parietal Bones (2): Paired bones forming most of the superior and lateral aspects of the cranium.

• Temporal Bones (2): Bones that form the inferolateral cranium and parts of the cranial floor.

  • Tympanic membrane (ear drum): The temporal bone contains the external auditory/acoustic meatus, a passageway that leads to the middle ear.

  • Mastoid process: Enlargement on the skull posterior to the ear lobe; site of attachment for muscles that move the skull.

  • Mandibular fossa: Depression on the temporal bone where the mandible articulates with the skull.

  • Styloid process: Slender projection below the ear; attachment for muscles and ligaments of the tongue and neck.

  • Zygomatic process: Projection that forms part of the cheekbone.

• Occipital Bone: Large bone forming most of the posterior wall and base of the skull.

  • Foramen magnum: Large opening for the spinal cord to connect with the brain.

  • Occipital condyle: Rounded projections that articulate with the first cervical vertebra (atlas).

• Sphenoid Bone: Butterfly-shaped bone in the middle of the skull forming the posterior wall of the orbits.

  • Optic foramen: Round hole in each posterior orbit; passageway for the optic nerve.

  • Sella turcica: Depression on the superior surface; houses the pituitary gland.

• Ethmoid Bone: Deep in the skull, between the nasal bones and the sphenoid.

  • Cribriform plate: Flat portion on either side of the crista galli; contains olfactory foramina for olfactory nerves.

  • Crista galli: Midline projection; attachment for brain membranes.

Sutures

• Sagittal suture: Between the two parietal bones along the midline of the skull.

• Squamous suture: Between the parietal bone and the temporal bone on either side of the skull.

• Coronal suture: Between the parietal bones and the frontal bone.

• Lambdoid suture: Between the occipital bone and the parietal bones.

Facial Bones

• Mandible: U-shaped lower jawbone; only movable bone of the skull.

  • Coronoid process: Projection for muscle attachment.

  • Mandibular condyle: Articulates with the temporal bone to form the temporomandibular joint.

• Maxillae (2): Upper jaw; forms most of the hard palate and upper teeth sockets.

• Palatine Bones (2): Form the posterior portion of the hard palate.

• Lacrimal Bones (2): Small bones in the medial wall of each orbit.

• Vomer: Forms the inferior part of the nasal septum.

• Inferior Nasal Conchae (2): Curved bones in the lateral walls of the nasal cavity.

• Zygomatic Bones (2): Cheekbones; form part of the lateral orbits.

• Nasal Bones (2): Form the bridge of the nose.

• Hyoid Bone: Not part of the skull; located in the anterior neck; only bone that does not articulate directly with another bone.

Vertebral Column

The vertebral column, or spine, supports the body, protects the spinal cord, and provides attachment points for ribs and muscles.

Abnormal Curvatures of the Spine

• Kyphosis: Exaggerated thoracic curvature ("hunchback").

• Lordosis: Exaggerated lumbar curvature ("swayback").

• Scoliosis: Abnormal lateral curvature.

Parts of a Vertebra

• Body (centrum): Thick, cylindrical, weight-bearing portion.

• Vertebral foramen: Opening formed by the vertebral body and arch; houses the spinal cord.

• Spinous process: Posterior projection; attachment for muscles and ligaments.

• Transverse process: Lateral projections; attachment for muscles and ligaments.

Types of Vertebrae

• Cervical vertebrae (C1–C7): Smallest, lightest vertebrae; found in the neck.

  • Transverse foramina: Openings for vertebral arteries.

  • Atlas (C1): Supports the skull; allows nodding "yes" motion.

  • Axis (C2): Has the dens (odontoid process); allows rotation "no" motion.

• Thoracic vertebrae (T1–T12): Articulate with ribs; have long spinous processes.

• Lumbar vertebrae (L1–L5): Large, sturdy vertebrae in the lower back.

• Sacrum (S1–S5): Five fused vertebrae; forms the posterior wall of the pelvis.

  • Sacral canal: Continuation of the vertebral canal.

  • Sacral hiatus: Inferior opening of the sacral canal.

• Coccyx (Co1–Co4): "Tailbone"; typically four fused coccygeal vertebrae.

Thoracic Cage

The thoracic cage protects vital organs and supports the shoulder girdles and upper limbs. It consists of the sternum, ribs, and thoracic vertebrae.

Sternum

• Manubrium: Superior portion; articulates with clavicles and first ribs.

• Body: Middle, largest portion.

• Xiphoid process: Inferior, smallest portion; site of muscle attachment.

Ribs (12 pairs)

• True ribs (1–7): Attach directly to the sternum via costal cartilage.

• False ribs (8–12): Do not attach directly to the sternum.

  • Floating ribs (11–12): No anterior attachment.

Lab Exam Preparation

• Be able to identify bones and structures on models or images.

• Understand the function and location of each structure.

• Exam question types may include multiple choice, matching, and labeling.

Additional info: For more detailed study, refer to Chapter 7: Axial Skeleton in your textbook and utilize available resources in your course's online platform.