Anatomy of Axial Skeleton

The Axial Skeleton

• Forms the longitudinal axis of the body
• Comprises 80 bones
• Includes the skull, vertebral column, thoracic cage, and associated bones

The Skull

• Protects the brain and entrances to the respiratory and digestive systems
• Comprises 22 bones
• 8 cranial bones form the braincase or cranium
• 14 facial bones protect and support the entrances to the digestive and respiratory tracts

The Cranial Bones

• The occipital bone forms the posterior and inferior surfaces of the cranium
• Articulates with the parietal, temporal, sphenoid bones, and the first cervical vertebra (atlas)
• Marks include the external occipital protuberance and external occipital crest

The Vertebral Column

• Comprises 24 vertebrae (7 cervical, 12 thoracic, 5 lumbar)
• Vertebrae are numbered from top to bottom (C1-L5)
• The sacrum articulates with the fifth lumbar vertebra and the coccyx
• The vertebral column has four curvatures: cervical, thoracic, lumbar, and sacral

Vertebral Anatomy

• Intervertebral foramina are gaps between pedicles of adjacent vertebrae for nerve connections to the spinal cord
• The vertebral canal is formed by the vertebral foramina and encloses the spinal cord
• Intervertebral discs are pads of fibrous cartilage that separate the vertebral bodies and absorb shocks

Vertebral Regions

• The cervical vertebrae (C1-C7) have small bodies, large vertebral foramina, and concave superior surfaces
• The thoracic vertebrae (T1-T12) have heart-shaped bodies, larger bodies than C1-C7, and costal facets for articulation with ribs
• The lumbar vertebrae (L1-L5) have oval-shaped bodies, thicker bodies than T1-T12, and no costal or transverse costal facets

Functions of the Axial Skeleton

• Supports and protects organs in body cavities
• Attaches to muscles of the head, neck, and trunk
• Involved in respiration and support for the appendicular skeleton

Vertebral Column

• The vertebral column consists of 33 vertebrae, divided into 5 regions: cervical, thoracic, lumbar, sacrum, and coccyx.
• Each region has distinct characteristics: cervical is smallest and most flexible, thoracic is intermediate in size and flexibility, and lumbar is largest and least flexible.
• The vertebral column supports the weight of the head and body, protects the spinal cord and nerves, and allows for flexibility and movement.

Cranium Structure

• The cranium is composed of 22 bones, including 8 cranial bones and 14 facial bones.
• The cranium is divided into three parts: calvaria (skullcap), base of the skull, and face.
• The cranium protects the brain and sensory organs and provides a base for the face and facial expressions.

Spinal Cord

• The spinal cord extends from the base of the brain to the level of the second lumbar vertebra (L2).
• The spinal cord is protected by the vertebral column and meninges (three layers of connective tissue).
• The spinal cord transmits messages between the brain and the rest of the body, controls involuntary actions, and interprets sensory information from the body.

Cranial Nerves

• There are 12 pairs of cranial nerves that emerge from the brain, controlling various functions, such as:
  • Olfactory (I): smell
  • Optic (II): vision
  • Oculomotor (III): eye movement
  • And others...

Skull Fractures

• There are four types of skull fractures: linear, depressed, basilar, and comminuted.
• Skull fractures can be caused by trauma, violence, or other means.
• Symptoms of skull fractures include headache, confusion or loss of consciousness, vomiting or nausea, seizures or convulsions, and clear fluid leaking from the nose or ears.