The state of euphoria caused by inert gases affects which part of the body?

The state of euphoria caused by inert gases, frequently referred to as "nitrogen narcosis," primarily affects the brain. This phenomenon occurs when divers experience an increase in nitrogen levels in their system during deeper dives, leading to changes in mental states, including a feeling of euphoria as well as impaired judgment and cognitive function.

Inert gases, such as nitrogen, can dissolve into the body's tissues under high pressure conditions typically experienced during diving. The higher partial pressure of nitrogen at depth can influence the brain’s neurotransmission, resulting in alterations in mood, perception, and thought processes. Therefore, the neurological effects underscore why the brain is the key organ impacted by the euphoria associated with inert gas exposure during diving.

The other options highlight organs and systems not primarily responsible for this sensation; while the lungs, heart, and muscles play roles in gas exchange, circulation, and physical exertion respectively, they do not directly generate the euphoric or altered cognitive states characterized by nitrogen narcosis.