Chapter 7: The Skeleton

7.1 The Skull Consists of 8 Cranial Bones and 14 Facial Bones

The skull is a complex structure composed of cranial and facial bones that protect the brain and form the framework of the face. Understanding the names, locations, and functions of these bones is essential in anatomy and physiology.

Major Regions of the Axial Skeleton

• Skull: Protects the brain and forms the structure of the face.

• Vertebral column: Supports the body and protects the spinal cord.

• Thoracic cage: Protects vital organs in the chest.

Cranial Bones: Names and Classification

• Paired cranial bones: Parietal bones, temporal bones

• Unpaired cranial bones: Frontal bone, occipital bone, sphenoid bone, ethmoid bone

Facial Bones: Names and Classification

• Paired facial bones: Maxillae, zygomatic bones, nasal bones, lacrimal bones, palatine bones, inferior nasal conchae

• Unpaired facial bones: Mandible, vomer

Identification of Skull Bones (A–N)

• N: Occipital bone

• E: Mandible

• L: Palatine bone

• H: Zygomatic bone

• K: Parietal bone

• J: Maxillary bone

• I: Frontal bone

• G: Temporal bone

• B: Ethmoid bone

• V: Vomer

• A: Lacrimal bone

• D: Inferior nasal concha

• M: Sphenoid bone

Functions of Skull Bone Markings

• H: Forms the prominence of the cheek (Zygomatic bone)

• L: Forms the posterior portion of the hard palate (Palatine bone)

• K: Forms most of the superior and lateral skull (Parietal bone)

• E: The largest bone of the face; the lower jawbone (Mandible)

• F, G: Forms the lateral skull surface (Temporal bone)

• C: Forms the bridge of the nose (Nasal bone)

• I: The keystone of the cranial floor (Frontal bone)

• B: Slender, plow-shaped bone that forms part of the nasal septum (Vomer)

• D: Projects medially from the lateral wall of the nasal cavity (Inferior nasal concha)

• M: Forms the anterior cranium (Sphenoid bone)

Major Skull Sutures and Connected Bones

Classification of Skull Bones by Shape

• Flat bones: Most skull bones are classified as flat bones.

Selected Skull Bone Markings and Functions

7.1b Functions of the Cranium and Facial Skeleton

The cranium and facial skeleton serve distinct but complementary roles in protecting vital organs and forming the structure of the face.

• Cranium: Serves as a protective encasement for the brain and organs of hearing and equilibrium. Shields the brain from external impacts and offers attachment sites for head and neck muscles, facilitating movement and support.

• Facial bones: Consist of 14 bones and play crucial roles such as the framework of the face, openings for air and food, cavities for sense organs, securing teeth, and muscle attachment.

7.1c Bony Boundaries of the Orbits, Nasal Cavity, and Paranasal Sinuses

Several bones contribute to the formation of the orbits, nasal cavity, and paranasal sinuses, which are important for protection, respiration, and sensory functions.

• Orbit bones: Frontal bone, sphenoid bone, zygomatic bone, maxillary bone, palatine bone, lacrimal bone, ethmoid bone

• Paranasal sinuses: Frontal bone, ethmoid bone, sphenoid bone, maxillary bone

• Functions of paranasal sinuses: Lighten the skull, warm and moisten air, enhance voice resonance, and mucus production

Unique Skull Bone

• Hyoid bone: The only bone in the body that does not articulate directly with any other bone. Located in the anterior middle of the neck, just below the mandible.

7.2 The Vertebral Column is a Flexible, Curved Support Structure

The vertebral column, or spine, is a central support structure composed of irregular bones called vertebrae. It protects the spinal cord and provides flexibility and resilience to the body.

Structure and Curvatures of the Vertebral Column

• Number of vertebrae: 26 irregular bones in the adult vertebral column

• Regions: 7 cervical, 12 thoracic, 5 lumbar, sacrum (5 fused), coccyx (4 fused)

• Curvatures: Cervical and lumbar curvatures are concave posteriorly; thoracic and sacral curvatures are convex posteriorly

• Intervertebral discs: Cushion-like pads sandwiched between vertebrae that act as shock absorbers

Structure of a Typical Vertebra

• Vertebral foramen: Opening for the spinal cord

• Spinous process: Posterior projection for muscle and ligament attachment

• Transverse process: Lateral projections for muscle attachment

• Pedicle: Connects the body to the arch

• Vertebral arch: Encloses the vertebral foramen

• Lamina: Forms the sides of the vertebral arch

• Body: Main weight-bearing region

• Superior articular facet: Articulates with adjacent vertebrae

Special Vertebrae and Features

• Atlas (C1): First cervical vertebra, supports the skull, allows nodding motion

• Axis (C2): Second cervical vertebra, has a peg-shaped dens that acts as a pivot for rotation

• C7 (vertebra prominens): Used as a landmark for counting vertebrae

• Thoracic vertebrae: Articulate with ribs

• Lumbar vertebrae: Receive the most stress, have large bodies

• Sacrum: Commonly called the tailbone, connects the spine to the hip bones via sacroiliac joints

Key Terms and Definitions

• Annulus fibrosus: Outer ring of intervertebral disc

• Nucleus pulposus: Inner gelatinous core of intervertebral disc

Equations and Formulas

• Number of vertebrae:

Comparisons and Classifications

• Flat bones vs. Irregular bones: Most skull bones are flat; vertebrae are irregular.

• Paired vs. Unpaired bones: Some cranial and facial bones are paired, others are unpaired.

Example Application

• Temporomandibular joint: Formed by the articulation of the mandibular fossa of the temporal bone and the condylar process of the mandible, allowing movement of the jaw.

Additional info: Academic context and expanded explanations have been added to ensure completeness and clarity for exam preparation.