Correction:
Nucleus dorsalis is Clarke's nucleus.
Main sensory nucleus is nucleus proprius.

Vertebral Levels of the Spinal Cord Segments:

• Spinal cord segments are present higher than their corresponding vertebrae due to the upward shift of the spinal cord during development.
• The rule 123 is applied to the vertebral spines:

1. In the cervical region: add one to the spine
C5 spine is opposite C6 cord segment (5 + 1).

2. In the upper thoracic region: add 2 to the spine
T4 spine is opposite T6 cord segment (4 + 2).

3. In the lower thoracic region: add 3 to the spine
T8 spine is opposite T10 cord segment (8 + 3).
T10 spine is opposite L1 cord segment (10 + 3).
T11 spine is opposite L2 to L5 cord segments.

4. T12 and L1 spines are opposite all sacral segments.