Overview of Skull Structure

Basic Structure of the Skull: Cranial and Facial Bones

The human skull is a complex structure composed of cranial and facial bones. These bones protect the brain and form the structure of the face.

• Cranial Bones: These bones encase and protect the brain. Major cranial bones include the frontal bone, parietal bones, temporal bones, occipital bone, sphenoid bone, and ethmoid bone.

• Facial Bones: These bones form the structure of the face and support the entrances to the digestive and respiratory systems. Key facial bones include the maxilla, zygomatic bone, nasal bone, mandible, lacrimal bone, palatine bone, inferior nasal concha, and vomer.

• Function: The skull protects the brain, supports sensory structures, and provides attachment points for muscles involved in chewing and facial expression.

Example: The mandible is the only movable bone of the skull, allowing for mastication (chewing).

Structure of the Vertebrae

Thoracic Vertebrae

The vertebral column is divided into regions, with the thoracic vertebrae forming the middle segment. These vertebrae articulate with the ribs and contribute to the thoracic cage.

• Body: The thick, disc-shaped anterior portion that bears weight.

• Vertebral Foramen: The opening through which the spinal cord passes.

• Transverse Process: Lateral projections for muscle and ligament attachment; in thoracic vertebrae, they also articulate with ribs.

• Spinous Process: Posterior projection for muscle and ligament attachment.

• Superior and Inferior Articular Facets: Articulate with adjacent vertebrae.

• Lamina and Pedicle: Form the vertebral arch, enclosing the vertebral foramen.

Example: The thoracic vertebrae (T1-T12) are distinguished by their articulation with the ribs.

The Sacrum and Coccyx

The sacrum and coccyx are located at the base of the vertebral column and are formed by the fusion of several vertebrae.

• Sacrum: A triangular bone formed by the fusion of five sacral vertebrae. It connects the spine to the hip bones (iliac bones) of the pelvis.

• Coccyx: Commonly known as the tailbone, it is formed by the fusion of three to five small vertebrae.

• Key Features:

  • Ala: Wing-like projections on either side of the sacrum.

  • Median Sacral Crest: Ridge formed by the fused spinous processes.

  • Sacral Foramina: Openings for the passage of nerves and blood vessels.

  • Auricular Surface: Articulates with the ilium of the pelvis.

  • Transverse Lines: Indicate the fusion of sacral vertebrae.

Example: The sacrum forms the posterior wall of the pelvic cavity and supports the weight of the upper body when sitting and standing.

The Pectoral Girdle

Structure of the Scapula

The pectoral girdle connects the upper limb to the axial skeleton and consists of the scapula (shoulder blade) and clavicle (collarbone). The scapula is a flat, triangular bone that provides attachment points for muscles and articulates with the humerus at the shoulder joint.

• Key Features of the Scapula:

  • Medial (Vertebral) Border: Closest to the vertebral column.

  • Lateral (Axillary) Border: Closest to the armpit.

  • Superior Angle: Uppermost point of the scapula.

  • Inferior Angle: Lowermost point of the scapula.

  • Glenoid Cavity (Fossa): Shallow socket that articulates with the head of the humerus.

  • Coracoid Process: Hook-like projection for muscle attachment.

  • Acromion: Lateral extension of the scapular spine; forms the highest point of the shoulder.

  • Supraspinous and Infraspinous Fossae: Depressions above and below the scapular spine for muscle attachment.

Example: The glenoid cavity of the scapula forms the socket of the ball-and-socket shoulder joint.

The Humerus and Forearm

Structure of the Humerus

The humerus is the long bone of the upper arm, articulating proximally with the scapula and distally with the radius and ulna.

• Head: Rounded proximal end that fits into the glenoid cavity of the scapula.

• Greater and Lesser Tubercles: Projections for muscle attachment.

• Shaft: The long, central portion of the bone.

• Distal End: Includes the capitulum and trochlea, which articulate with the radius and ulna, respectively.

Example: The olecranon fossa on the posterior distal humerus accommodates the olecranon process of the ulna during elbow extension.

Bones of the Forearm: Radius and Ulna

The forearm consists of two parallel long bones: the radius (lateral, thumb side) and the ulna (medial, little finger side). These bones articulate with each other and with the humerus and carpal bones.

• Radius: Located on the lateral side of the forearm; its head articulates with the capitulum of the humerus and the radial notch of the ulna.

• Ulna: Located on the medial side; its olecranon process forms the bony prominence of the elbow.

• Interosseous Membrane: A fibrous sheet connecting the radius and ulna along their lengths.

Example: The radial tuberosity serves as the attachment site for the biceps brachii muscle.

Summary Table: Key Bones and Features

Additional info: The above notes expand on the labeled diagrams and brief points in the provided materials, offering definitions, anatomical context, and examples for each major bone and region.