Dear Doctor Column, November 18, 2002

Question:

What happens when we cry? What part of the eye do tears come from? Why does our voice sound funny when we cry? Why do we cry when we watch a sad movie? Can people who are blind shed tears? Any information will help.

Answer:

Answers to these questions provide considerable insight into how the body works. Part of the answer comes from the construction of the eye's tear drainage system; the other from how the human nervous system controls involuntary functions.

Tears flow from glands (the lacrimal glands) arranged around the eyes. These glands constantly release a small amount of liquid to wash away debris that settles on the front of the eyes. This constant flow of liquid moisturizes the eyes and helps to keep vision clear. We produce tears whether we are awake, asleep, happy, or sad. Tears produced when our eyes are irritated, for example by onions, are called reflex tears; emotional tears occur when we have strong feelings.

The main lacrimal glands are located just underneath the bony areas of the skull beneath the outer edges of the eyebrows. Tiny ducts, which line the upper and lower eyelids and the inner edges of the eyelids next to the nose, carry tear fluid from the tear glands to the surface of the eyes and then drain into the nasal cavity and then into the throat. The amount of fluid in these tubes is normally small, and we rarely notice the extra fluid in the nose. However, when we cry, excess tears flow through the system. The result: the runny nose and voice changes associated with crying.

The other physical changes associated with crying, such as swollen eyes, a red nose, and puffy face, occur because of why we start crying. Humans have two nervous systems, which control every part of the body. The first one, called the parasympathetic nervous system, is controlled by parts of the brain responsible for our day-to-day involuntary bodily functions, such as digestion, breathing, and the beating of our hearts.

The body's other nervous system, called the sympathetic nervous system, is controlled by centers of the brain and spinal cord that respond to stressful conditions, such as danger or strong emotions. When danger, anger, or fear activates the sympathetic nervous system, we experience a "fight or flight" response. Adrenalin surges through our bodies. Pupils dilate, the lacrimal glands secrete more fluid, the heart begins pumping more blood more rapidly, breathing increases to bring in more oxygen, muscles tense, and our senses stand ready to respond to danger. The body reacts to any strong emotion, such as crying, in this manner. The face becomes flushed and puffy, the facial muscles twitch, and the throat constricts, further changing the quality of the voice.

It's possible that an injury that results in blindness can also cause damage to the anatomical structure of the eye, which, in turn, can affect the lacrimal glands and tear ducts. Typically, however, just because a person is blind does not mean that they do not produce tears and cry just like everyone.