Axial Skeleton

Vertebral Column

The vertebral column is a central structure of the axial skeleton, providing support and protection for the spinal cord. It consists of a series of vertebrae grouped into regions.

• Regions:

  • Cervical: 7 vertebrae (C1–C7)

  • Thoracic: 12 vertebrae (T1–T12)

  • Lumbar: 5 vertebrae (L1–L5)

  • Sacrum: Fused 5 vertebrae

  • Coccyx: Fused 3–5 small vertebrae

• Intervertebral Discs: Fibrocartilaginous pads between vertebrae that absorb shock and allow movement.

Structure of Typical Vertebrae

Most vertebrae share common structural features that support their function.

• Body (centrum): Main weight-bearing portion.

• Vertebral arch: Encloses the vertebral foramen.

  • Pedicles

  • Laminae

• Processes:

  • Spinous process

  • Transverse processes

  • Superior and inferior articular processes

• Vertebral foramen: Canal for spinal cord.

• Intervertebral foramina: Openings for spinal nerves.

Cervical Vertebrae

Cervical vertebrae have unique features to support head movement and protect neural structures.

• C1 (Atlas): Lacks a body; superior articular facets articulate with occipital condyles, allowing nodding motion.

• C2 (Axis): Has a vertical process called the Odontoid process or Dens, allowing rotation of the head.

• C3–C6: Vertebral foramen is triangular; spinous process is bifurcated (two branches).

• C7 (Vertebra Prominens): Prominent spinous process; not bifurcated.

Thoracic Vertebrae (T1–T12)

Thoracic vertebrae articulate with ribs and have distinctive features.

• Heart-shaped body

• Articulate with ribs via costal facets

• Round vertebral foramen

• Long spinous processes

Lumbar Vertebrae (L1–L5)

Lumbar vertebrae are the largest and strongest, supporting most of the body's weight.

• Large bodies

• Thick, hatchet-shaped spinous processes

• Spinal cord ends at the superior edge of L1–L2; the lower canal contains cauda equina and cerebrospinal fluid

Sacrum and Coccyx

The sacrum and coccyx are formed by the fusion of vertebrae and provide attachment points for ligaments and muscles.

• Sacrum:

  • Formed from fusion of 5 vertebrae

  • Features: Median sacral crest, sacral foramina, sacral canal, auricular surface

• Coccyx:

  • Fusion of 3–5 small, irregularly shaped vertebrae

  • Attached to sacrum by ligaments

The Bony Thorax

Sternum

The sternum is a flat bone forming the anterior portion of the thoracic cage.

• Manubrium: Superior part; features jugular notch and sternal angle

• Body: Main central portion

• Xiphoid process: Inferior tip

Ribs

The ribs protect thoracic organs and support breathing.

• 12 pairs

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

• False ribs (8–10): Attach indirectly to sternum via cartilage

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

Appendicular Skeleton

Pectoral (Shoulder) Girdle

The pectoral girdle connects the upper limb to the axial skeleton and allows a wide range of motion.

• Clavicle:

  • Sternal end

  • Acromial end

  • Conoid tubercle

• Scapula:

  • Acromion process

  • Coracoid process

  • Subscapular notch

  • Glenoid cavity

• Borders: Superior, medial (vertebral), lateral (axillary)

• Angles: Superior, inferior, lateral

• Fossae: Infraspinous, supraspinous, subscapular

The Upper Arm

The humerus is the major bone of the upper arm, articulating with the scapula and forearm bones.

• Humerus:

  • Head

  • Anatomical neck

  • Surgical neck

  • Greater and lesser tubercles

  • Intertubercular sulcus

  • Deltoid tuberosity

  • Lateral and medial epicondyles

  • Trochlea, capitulum

  • Radial fossa, coronoid fossa, olecranon fossa

Forearm

The forearm consists of the radius and ulna, which articulate with each other and the humerus.

• Radius:

  • Radial tuberosity

  • Head

  • Neck

  • Ulnar notch

  • Styloid process

• Ulna:

  • Olecranon process

  • Coronoid process

  • Trochlear notch

  • Radial notch

  • Head

  • Styloid process

Hand

The hand consists of carpal bones (wrist), metacarpals (palm), and phalanges (fingers).

• Carpals: Eight wrist bones arranged in two rows.

  • Scaphoid, lunate, triquetrum (triangular), pisiform (proximal row)

  • Trapezium, trapezoid, capitate, hamate (distal row)

• Metacarpals: Numbered 1–5 from thumb (pollex) to little finger

• Phalanges: Each finger has proximal, middle, and distal phalanges; thumb (pollex) has only proximal and distal

Table: Classification of Ribs

Additional info:

• The vertebral column's curvature and intervertebral discs contribute to flexibility and shock absorption.

• The pectoral girdle's structure allows for a wide range of upper limb movement, essential for manipulation and locomotion.

• Carpal bone arrangement is crucial for wrist flexibility and strength.