Axial Skeleton Notes

Axial Skeleton Overview

  • The axial skeleton consists of the skull, vertebral column, and thoracic cage, which collectively support the head and trunk.

Skull

  • Comprised of:
    • 8 Cranial Bones: Protects the brain.
    • 14 Facial Bones: Protects facial structures and supports sensory organs.
    • 6 Auditory Ossicles: Transfer and amplify sound vibrations.

Cranial Bones

  1. Frontal Bone

    • Description: Single bone forming the front of the skull.
    • Function: Protects the frontal lobes of the brain.

  2. Parietal Bones (2)

    • Description: Paired curved bones forming the middle segment of the cranial dome.
    • Function: Protects the parietal lobes of the brain.

  3. Occipital Bone

    • Description: Single posterior bone at the base of the skull.
    • Function: Protects the occipital lobe.

  4. Temporal Bones (2)

    • Description: Paired bones on the sides of the cranium.
    • Function: Protects the temporal lobe.

  5. Sphenoid Bone

    • Description: Wedge-shaped bone with a central body and extended wings.

  6. Ethmoid Bone

    • Description: Single bone forming the middle portion of the anterior cranial floor.
    • Function: Forms part of the orbit, nasal cavity, septum, and anterior cranial fossa.

Facial Bones

  • 14 facial bones that serve various functions:

  1. Maxillae (2)

    • Description: Upper jaw bones that house the upper teeth.

  2. Nasal Bones (2)

    • Description: Paired bones that comprise the strongest part of the nose and support the nasal septum.

  3. Lacrimal Bones (2)

    • Description: Thin bones in the medial wall of the orbit, supporting the lacrimal apparatus.

  4. Palatine Bones (2)

    • Description: Form the posterior third of the hard palate; contribute to oral cavity, nasal cavity, and orbits.

  5. Inferior Nasal Conchae (2)

    • Description: Thin-curved bones that project from the lateral walls of the nasal cavity.

  6. Zygomatic Bones (2)

    • Description: Cheekbones providing shape to the face.

  7. Vomer

    • Description: Bone forming the lower portion of the nasal septum.

  8. Mandible

    • Description: Single lower jawbone.

Auditory Ossicles

  • 6 small bones that transmit sound.

  1. Malleus (2)

    • Function: Attached to the tympanic membrane, known as the hammer.

  2. Incus (2)

    • Function: Known as the anvil, transmits vibrations from malleus to stapes.

  3. Stapes (2)

    • Function: Base covers the round window of the cochlea.

Vertebral Column

  • Composed of:
    • 24 single vertebrae: Cervical (C1-C7), Thoracic (T1-T12), Lumbar (L1-L5)
    • 2 fused bones: Sacrum and Coccyx

Types of Vertebrae

  1. Cervical Vertebrae (C1-C7)

    • Atlas (C1): Lacks a body, allows nodding of the head.
    • Axis (C2): Contains the dens for rotation.

  2. Thoracic Vertebrae (T1-T12)

    • Position: Posterior thorax; articulates with ribs.

  3. Lumbar Vertebrae (L1-L5)

    • Function: Provides stability to the back.

  4. Sacrum

    • Description: Composed of 5 fused vertebrae.

  5. Coccyx

    • Description: Composed of 4 fused coccygeal vertebrae; known as tailbone.

Thoracic Cage

  • Composed of:
    • 12 pairs of ribs
    • Sternum

Ribs

  1. True Ribs: Superior 7 pairs.
  2. False Ribs: Remaining 5 pairs (8-12).
  3. Floating Ribs: 11th and 12th ribs that do not attach to the sternum.

Sternum (Breastbone)

  • Composed of:
    • Manubrium: Upper part.
    • Body: Middle section.
    • Xiphoid Process: Lower part, at the 5th intercostal space.

Hyoid Bone

  • A unique, freely floating bone in the neck aiding in the swallowing process.