The Atlas (C1 Vertebra) & The Axis (C2 Vertebra)

A. The Atlas (C1 Vertebra)

The atlas is the first cervical vertebra, specialized to support the skull. It has no body or spinous process, allowing greater motion. It forms joints with the occiput (atlanto-occipital joint) and with the axis (atlanto-axial joint). It transmits the vertebral artery and spinal nerve, and its lesions can lead to headaches, dizziness, and visual symptoms.

Key Features:

• No body or spinous process. 
• Articulates with the skull and axis.
• Supports nodding and slight rotation. 
• Important structures: vertebral artery, C1 spinal nerve. 
• Clinical importance in headache, vertebrobasilar insufficiency

Questions & Answers: 

1. Why is it called the atlas?

Ans- It supports the skull, like Atlas held up the sky in Greek mythology.

2. What joint does it form with the skull? 

Ans- Atlanto-occipital joint. 

3. What unique feature does it lack?

Ans- It has no vertebral body or spinous process

4. What artery passes through the transverse foramen? 

Ans- Vertebral artery. 

5. Clinical sign of atlas misalignment?

Ans - Headache, neck stiffness, dizziness.

6. Main motion allowed? 

Ans- Flexion-extension (nodding).

7. Important related nerve? 

Ans- Suboccipital nerve (C1)

B. The Axis (C2 Vertebra)

The axis (C2) is the second cervical vertebra. It is unique because of a bony projection called the dens (odontoid process) that acts like a pivot, allowing the atlas (C1) and skull to rotate side to side ("no" movement). The atlas rotates around the dens, making this the most mobile vertebral joint in the spine.

Key Features:

• Function: Supports rotation of the head (side-to-side)
• Special feature: Dens (odontoid process)
• Joint formed: Atlanto-axial joint (C1-C2)
• No intervertebral disc between C1 and C2
• Vulnerable to injury, but vital for head mobility
• Spinal cord and vertebral artery are closely related — making lesions here serious

Questions & Answers

1.  What is the main function of the dens?
   Ans: It serves as a pivot that the atlas (C1) and skull rotate around.

2. What joint is formed between the atlas and axis?
   Ans: The atlanto-axial joint.

3. What happens if the transverse ligament (which holds the dens) is damaged?
   Ans: The dens can press on the spinal cord — a potentially fatal condition.

4. What movements are allowed at the atlanto-axial joint?
   Ans: Rotation (side-to-side head turning).

5. Why is there no intervertebral disc between C1 and C2?
   Ans: To allow free pivot movement and reduce resistance during rotation.

6. Which nerve is related to C2?
   Ans: The greater occipital nerve - it may be involved in tension headaches.

Clinical Insight:

A rotated or misaligned axis can cause:

1. Vertigo or balance problems
2. Neck stiffness,
3. Irritation of the vertebral artery
4. Headaches (especially at the back of the head)
5. Gentle manual correction can relieve symptoms and restore head movement.