If the measured distance from the nasion to the inion is 32 cm, what is the distance from the inion to Oz?

The correct answer is based on understanding cranial anatomy and the standard measurements used in sleep studies or neuromonitoring. The nasion is the bridge of the nose, and the inion is the external occipital protuberance at the back of the skull. Oz refers to the midline occipital electrode site found in the 10-20 system of electrode placement, which is a standard system used for electroencephalography (EEG) and other neurophysiological measures.

In the 10-20 system, the distance from the nasion to the inion is typically divided into segments to determine the placement of electrodes. A useful reference point commonly used in cranial measurements is that the distance from the inion to Oz is approximately 20% of the total distance from nasion to inion.

If the measured distance from nasion to inion is 32 cm, calculating 20% of this distance results in approximately 6.4 cm (0.20 x 32 cm = 6.4 cm). This is the accepted value for the distance from the inion to Oz, making it the correct choice in this context. Thus, knowing the proportions used in cranial measurements helps clarify why this