Lecture Notes: The Axial Skeleton

Introduction

• Focus on the axial skeleton, part of the skeletal system.
• Lecture combines material from lectures and lab sessions.
• Highlight: Common problematic bones for students will be discussed.
• Adult skeleton typically has 206 bones; variability due to fusion or non-fusion of bones.

Axial Skeleton Overview

• Composed of the skull, vertebral column, and thoracic cage.
• Provides an axis for appendages (arms and legs).

Skull

• Cranial Bones: Form the cranium to enclose the brain.
• Facial Bones: Form the face, protect digestive and respiratory entrances, attach facial muscles.
• Importance of facial features in communication and protection.

Skull Anatomy

• Vomer Bone: Small, plow-like bone in the nasal cavity, part of the nasal septum.
• Zygomatic Arch: Composed in part by the zygomatic bone and its temporal process.
• Mandible: Lower jaw; includes coronoid process, mandibular condyle, ramus, angle, body, and mental foramen.

Cavities of the Skull

• Cranial Cavity: Encloses and supports the brain.
• Other cavities: orbits, oral cavity, nasal cavity, and paranasal sinuses (frontal, ethmoid, maxillary, sphenoidal).
• Sinuses lighten skull, humidify/warm air, and add resonance to the voice.

Ethmoid Bone

• Challenging for students; involves orientation.
• Crista Galli: Projects upward, part of cranial cavity.
• Perpendicular Plate: Forms nasal septum.

Sutures of the Skull

• Immovable fibrous joints in the skull.
• Key Sutures: Coronal, Sagittal, Lambdoid.
• Fontanelles: "Soft spots" in infant skulls, allow for passage during birth.

Orbital Complex

• Composed of seven bones: frontal, lacrimal, zygomatic, maxilla, palatine, ethmoid, sphenoid.
• Palatine Bone: Contains horizontal plate, contributes to the orbit.

Auditory Ossicles

• Tiny bones in the ear: malleus (hammer), incus (anvil), stapes (stirrup).

Hyoid Bone

• Does not articulate with other bones; attachment for tongue and larynx muscles.
• Important in forensic science (e.g., determining cause of death).

Vertebral Column

• Composed of 26 bones: 24 individual vertebrae (7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 3-5 coccygeal).
• Functions: support, protection of spinal cord, weight transfer.

Vertebrae Specifics

• Basic Structures: Body, spinous process, transverse processes, lamina, pedicle.
• Atlas (C1) & Axis (C2): Unique vertebrae; atlas supports skull, axis allows rotational movement.

Sacrum and Coccyx

• Sacrum: Contains sacral promontory, median sacral crest, auricular surface.

Thoracic Cage

• Composed of thoracic vertebrae, ribs, sternum.
• Protects heart, lungs, trachea, esophagus.
• Sternum Parts: Manubrium, body, xiphoid process.

Ribs

• 12 pairs total:
  • True Ribs (1-7): Direct attachment to the sternum.
  • False Ribs (8-10): Indirect or no attachment to the sternum.
  • Floating Ribs (11-12): No attachment to the sternum.
• Rib Anatomy: Shaft (main body), costal groove (indented along the shaft).