The Science of Bodily Functions

Why We Yawn, Sneeze, Burp, and More

Have you ever coughed, sneezed, or gotten goosebumps and wondered, "What's the point?" Although they can be annoying, bodily functions like these help to protect the body and keep it functioning normally. We can control some of our bodily functions, but others are involuntary reflex actions, over which we do not have control. Others may be controlled both voluntarily and involuntarily.

Why Do We Yawn?

Baby Yawning
Baby Yawning. Multi-bits/The Image Bank/Getty Images

Yawning not only occurs in humans but in other invertebrates as well. The reflex reaction of yawning often happens when we are tired or bored, but scientists don't fully understand its purposes. When we yawn, we open our mouths wide, suck in a large volume of air, and exhale slowly. Yawning involves stretching of the muscles of the jaw, chest, diaphragm, and windpipe. These actions help to get more air into the ​lungs.

Research studies indicate that yawning helps to cool the brain. When we yawn, our heart rate increases and we breath in more air. This cooler air is circulated to the brain bringing its temperature down to a normal range. Yawning as a means of temperature regulation helps to explain why we yawn more when it is time for sleep and upon waking up. Our body temperatures fall when it is time for sleep and rise when we wake up. Yawning also helps to relieve pressure build up behind the eardrum that occurs during changes in altitude.

An interesting aspect of yawning is that when we observe others yawn, it often inspires us to yawn. This so-called contagious yawning is thought to be the result of empathy. When we understand what others are feeling, it causes us to place ourselves in their position. When we see others yawn, we spontaneously yawn. This phenomenon not only happens in humans but also in chimpanzees and bonobos.

Why Do We Get Goosebumps?

Goosebumps. Bele Olmez/Getty Images

Goosebumps are small bumps that appear on the skin when we are cold, afraid, excited, nervous, or under some type of emotionally stressful situation. It is believed that the term "goosebump" was derived from the fact that these bumps resemble the skin of a plucked bird. This involuntary reaction is an autonomic function of the peripheral nervous system. Autonomic functions are those that do not involve voluntary control. So when we get cold, for instance, the ​sympathetic division of the autonomic system sends signals to the muscles on your skin causing them to contract. This causes tiny bumps on the skin, which in turn cause the hairs on your skin to rise. In hairy animals, this reaction helps to insulate them from cold by helping them to conserve heat.

Goosebumps also appear during frightening, exciting, or stressful situations. During these events, the body prepares us for action by accelerating heart rate, dilating pupils, and increasing metabolic rate to provide energy for muscle activity. These actions occur to prepare us for a fight or flight response that occurs when faced with potential danger. These and other emotionally charged situations are monitored by the brain's amygdala, which activates the autonomic system to respond by preparing the body for action.

Why Do We Burp and Pass Gas?

Burping Baby
Dad burping his baby. Ariel Skelley/DigitalVision/Getty Images

A burp is the releasing of air from the stomach through the mouth. As digestion of food occurs in the stomach and intestines, gas is produced in the process. Bacteria in the digestive tract help to break down food but also generate gas. The releasing of extra gas from the stomach through the esophagus and out of the mouth produces a burp or belch. Burping can be either voluntary or involuntary and can occur with a loud sound as the gas is released. Babies need assistance in order to burp as their digestive systems are not fully equipped for burping. Patting a baby on the back can help to release the extra air gulped during feeding.

Burping can be caused by swallowing too much air as often happens when eating too fast, chewing gum, or drinking through a straw. Burping can also result from consuming carbonated drinks, which increase the amount of carbon dioxide in the stomach. The type of food we eat can also contribute to excess gas production and burping. Foods such as beans, cabbage, broccoli, and bananas can increase burping. Any gas that is not released by burping travels down the digestive tract and is released through the anus. This release of gas is known as flatulence or a fart.

What Happens When We Sneeze?

Woman Sneezing
Woman sneezing releasing moisture into the air. Martin Leigh/Oxford Scientific/Getty Images

Sneezing is a reflex action caused by irritation in the nose. It is characterized by the expulsion of air through the nose and mouth at a high rate of speed. Moisture within the respiratory tract is expelled into the surrounding environment.

This action removes irritants such as pollen, mites, and dust from the nasal passages and respiratory area. Unfortunately, this action also helps to spread bacteria, viruses, and other pathogens. Sneezing is stimulated by white blood cells (eosinophils and mast cells) in the nasal tissue. These cells release chemicals, such as histamine, that cause an inflammatory response resulting in swelling and the movement of more immune cells to the area. The nasal area also becomes itchy, which helps to stimulate the sneezing reflex.

Sneezing involves the coordinated action of a number of different muscles. Nerve impulses are sent from the nose to the brain center that controls the sneeze response. Impulses are then sent from the brain to the muscles of the head, neck, diaphragm, chest, vocal cords, and eyelids. These muscles contract to help expel the irritants from the nose.

When we sneeze, we do so with our eyes closed. This is an involuntary response and may occur to protect our eyes from germs. Nose irritation is not the only stimulus for the sneeze reflex. Some individuals sneeze due to sudden exposure to bright light. Known as photic sneezing, this condition is an inherited trait.

Why Do We Cough?

Woman coughing.
Woman coughing. BSIP/UIG/Getty Images

Coughing is a reflex that helps to keep respiratory passages clear and keep irritants and mucus from entering the lungs. Also called tussis, coughing involves a forceful expulsion of air from the lungs. The cough reflex starts with irritation in the throat that triggers cough receptors in the area. Nerve signals are sent from the throat to cough centers in the brain found in the brainstem and pons. The cough centers then send signals to the abdominal muscles, diaphragm, and other respiratory muscles for coordinated involvement in the coughing process.

Coughing is produced as air is first inhaled through the windpipe (trachea). Pressure then builds in the lungs as the opening of the airway (larynx) closes and respiratory muscles contract. Finally, the air is rapidly released from the lungs. A cough can also be produced voluntarily.

Coughs can happen suddenly and be short-lived or may be chronic and last for several weeks. Coughing may indicate some type of infection or disease. Sudden coughs may be the result of irritants such as pollen, dust, smoke, or spores inhaled from the air. Chronic coughing may be associated with respiratory diseases such as asthma, bronchitis, pneumonia, emphysema, COPD, and laryngitis.

What's the Purpose of a Hiccup?

Woman Covering Mouth
Hiccups are involuntary reflexes. drbimages/E+/Getty Images

Hiccups result from involuntary contractions of the diaphragm. The diaphragm is the dome-shaped, primary muscle of respiration located in the lower chest cavity. When the diaphragm contracts, it flattens increasing volume in the chest cavity and causing pressure to decrease in the lungs. This action results in inspiration or the breathing in of air. When the diaphragm relaxes, it returns to its dome-shape reducing volume in the chest cavity and causing pressure to rise in the lungs. This action results in the expiration of air. Spasms in the diaphragm cause a sudden intake of air and the widening and closing of the vocal cords. It is the closing of the vocal cords that create the hiccup sound.

It is not known why hiccups occur or their purpose. Animals, including cats and dogs, also get hiccups from time to time. Hiccups are associated with: drinking alcohol or carbonated drinks, eating or drinking too quickly, eating spicy foods, changes in emotional states, and sudden temperature changes. Hiccups don't normally last for long, however, they can last for a while due to nerve damage of the diaphragm, nervous system disorders, or gastrointestinal problems.

People will do strange things in an attempt to cure a bout of hiccups. Some of which include pulling on the tongue, screaming for as long as possible, or hanging upside down. Actions that seem to help stop hiccups include holding your breath or drinking cold water. However, none of these actions is a sure bet to stop hiccups. Almost always, hiccups will eventually stop on their own.


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Bailey, Regina. "The Science of Bodily Functions." ThoughtCo, Feb. 16, 2021, Bailey, Regina. (2021, February 16). The Science of Bodily Functions. Retrieved from Bailey, Regina. "The Science of Bodily Functions." ThoughtCo. (accessed April 14, 2021).