The bullet that sliced through the neck of Boston Marathon bomb suspect Dzhokhar Tsarnaev likely missed his major arteries and windpipe, experts said.
Otherwise, he would have been dead within minutes.
"If you think about it, [the neck has] got a lot of very important structures in a very small, confined space," said Dr. Elliott Haut, a professor of surgery at Johns Hopkins University School of Medicine.
About 20 percent of the blood from the heart goes to the brain via the carotid artery, which is about as thick as a thumb and is located in the neck . Haut said injuring it could cause a patient to bleed out in about five minutes. The jugular vein, which carries used blood back down from the brain, is also in the neck and could be life-threatening if damaged.
"When we talk about survivability, the main thing we're talking about is bleeding," said Dr. Gaelyn Garrett of the Vanderbilt Voice Center, many of whose patients have self-inflicted gunshot wounds to the head. "The fact that he was able to climb out of the boat makes you think that he did not have an acutely life threatening wound."
Tsarnaev, 19, was taken into custody Friday night after being cornered in a backyard boat in Watertown. He was bleeding heavily and a federal complaint said he was wounded in the head, the neck, legs and hand.
Investigators have not been able to determine whether head and neck wounds were self-inflicted, sources told ABC News.
Garrett said patients survive suicide attempts "more often than you'd think." They often have injuries to their eyes, jaw bones, mouths, throats, tongues and vocal chords, requiring them to undergo rehabilitation. Carotid artery injuries can also result in brain damage because blood can't carry oxygen to the brain.
Since the windpipe is also located in the neck, Haut said trauma doctors are trained to check airways as soon as the patient arrives in the trauma bay.
"The first thing we think about is whether this person is able to breathe," Garrett said, adding that breathing can be interrupted by blood in the airway, nerve damage and swelling.
Doctors then assess whether the patient can swallow and communicate, she said.
Tsarnaev has begun communicating with law enforcement in writing, sources told ABC News, but it's not clear whether this is necessary because of a neck injury or because he is on a ventilator.