21 of the most iconic photos ever taken. The image of a napalm scarred little girl running from her burning village in Vietnam is one of the most well known photographs in the world. Kim Phuc, the girl featured in the image, is now receiving free laser surgery to cover her scars, 40 years after that terrible day.
1 Oxygen: Specialized nerve cells within the aorta and carotid arteries called peripheral chemoreceptors monitor the oxygen concentration of the blood and feed back on the respiratory centers. 2  If the oxygen concentration in the blood decreases, they tell the respiratory centers to increase the rate and depth of breathing. This mechanism prevents damage to the lungs that would be caused by over-inflation. 2  Signals from higher brain centers: Nerve cells in the hypothalamus and cortex also influence the activity of the respiratory centers. 3  During pain or strong emotions, the hypothalamus will tell the respiratory centers to speed up.
The medulla, located nearest the spinal cord, directs the spinal cord to maintain breathing, and the pons, a part of the brain very near the medulla, provides further smoothing of the respiration pattern. This control is automatic, involuntary and continuous.