How many vertebrae are present in the human adult spine?

The adult human spine typically contains a total of 33 vertebrae, which are categorized into different regions: cervical (7), thoracic (12), lumbar (5), sacral (5 fused into 1 sacrum), and coccygeal (4 fused into 1 coccyx).

Cervical, thoracic, and lumbar vertebrae are individually counted, while the sacral and coccygeal vertebrae are fused into single structures in adult life. This amalgamation explains why the total number of vertebrae reaches 33 in adults, as some vertebrae that are separate during infancy become fused later on. Understanding this breakdown helps in recognizing the structure and function of the spine across different ages and developmental stages.

The other options do not accurately reflect the total number of individual vertebrae in an adult spine. 24, 30, and 26 do not account for the full structure of the adult spine, which includes the total of 33 vertebral elements that make it up.