The neurons in Phil Ivey's cerebral cortex require an adequate supply of oxygen in order to function properly. To compensate for this demand the body relies heavily on the respiratory organ system to gather oxygen from the surrounding atmosphere which is made up of approximately ~78% nitrogen, ~21% oxygen, and ~1% various other components.
In order for the respiratory system to transfer oxygen into the bloodstream the lungs expand and fill with air. When Phil Ivey yawns, the lungs expand fully to maximize air volume and surface area within the lungs. This maximizes oxygen transfer to the red blood cells. The oxygen molecules adhere to the iron contained within the red blood cells. The red blood cells then transfer the oxygen molecules throughout the body via the circulatory system. Once the oxygen molecules reach the neurons within Phil Ivey's cerebral cortex, the oxygen is transferred to the neurons via osmosis.
The neurons in Phil Ivey's cerebral cortex require an adequate supply of oxygen in order to function properly. To compensate for this demand the body relies heavily on the respiratory organ system to gather oxygen from the surrounding atmosphere which is made up of approximately ~78% nitrogen, ~21% oxygen, and ~1% various other components.
In order for the respiratory system to transfer oxygen into the bloodstream the lungs expand and fill with air. When Phil Ivey yawns, the lungs expand fully to maximize air volume and surface area within the lungs. This maximizes oxygen transfer to the red blood cells. The oxygen molecules adhere to the iron contained within the red blood cells. The red blood cells then transfer the oxygen molecules throughout the body via the circulatory system. Once the oxygen molecules reach the neurons within Phil Ivey's cerebral cortex, the oxygen is transferred to the neurons via osmosis.
You forgot to mention that the increase in oxygen helps seratonin uptake, which increases neural processing power. This process also helps to inhibit melatonin, a sleep hormone. If the initial yawning fails to create proper homeostasis, then negative feedback informs the visceral cranial nerve to increase the involuntary movement of the diaphram, causing another yawn. In severe cases, sleep may be warranted.