The Science Behind the Goose Bump

The skin is the largest organ in the human body. Most people don’t realize the critical role skin plays in the survival of multi-cellular organisms. The skin is air tight and provides a mechanical and defensive barrier between the outside environment and the body’s internal structures. It is what holds us together, gives us shape, if you will, and this multifaceted structure is perhaps the less appreciated out of all the body’s organs. The skin contains blood vessels, nerves, sweat glands, specialized glands to ward off pathogens, immune cells, sense receptors, hair, and muscle. And that’s not even the half of it. Within the skin’s three distinctly different layers, its components are specifically  arranged to produce a dynamic organ with the capabilities to repair itself. It is for these reasons, and many more, that makes the skin one of the most interesting organs of the body.

Many of the skin’s functions developed out of our need to survive. For example, the malanocyte is a specialized skin cell that helps the body ward off ultraviolet radiation by darkening our skin.

skinAnother evolutionary adaptation is the goose bump, that prickly raising of the skin that occurs when one is cold or senses danger. What exactly is the goose bump, and why is it important? Let’s take a look at a  simplified cross-section of human skin. As mentioned, mammalian skin has three layers. The epidermis, the dermis and the hypodermis. Each hair is contained in a sheath of epidermal cells called a hair follicle. This follicle is associated with sebaceous glands, capillaries, and a microscopic smooth muscle bundle called the arrector pili. This tiny muscle bundle attaches the hair follicle to the underside of the epidermis.

Let’s now look at the mechanics of the goose bump formation. Ordinarily, the hair emerges from the skin at an angle. When the arrector pili muscle fibers contract, this action pulls the lower half of the hair follicle toward the epidermis, resulting in the hair standing more erect. The result of this creates a “bumping” of the skin surrounding the shaft of hair above the skin. You now have a goose bump.

So, that’s the mechanics, now let’s take a look at the cause of a goose bump. Goose bumps are the effect of activation of the sympathetic branch of the autonomic nervous system. As mentioned above, the skin is innervated by nerves. Nerve cells respond to stimuli in the body and produce neurotransmitters, small molecules that bind to receptors on a cell surface.  The arrector pili muscle cells contain alpha 11) adrenergic receptors which bind to the neurotransmitter norepinephrine. The release of norepinephrine from the neuron follows the “fight-or-flight” response. When a person senses danger, surprise, or the body is under certain stress, the neuron receives a message and responds by releasing nor-epi. Norepinephrine then binds to the cell surface, and series of events occur within the cell that causes the arrector pili to contract.

Why do we have goose bumps? The answers are quite simple. Our ancestors had more hair than we did. To withstand the frigid temperatures the arrector pili was stimulated, causing the hairs to stand on end and trapping warmer air closer to the skin. It provided our ancestors with the thermal layer they needed. Erect hair also shows dominance. This is seen today when the hairs of a dog stand on end. Perhaps long ago our ancestors displayed the same sort of aura to their rivals. Imagine 150,000 years ago if you were face to face with your enemy who had hair sticking out like a pekingese dog. My guess would be you would do more than laugh. In a more practical sense, when someone becomes frightened or threatened, the “fight-or-flight” response kicks in, and a host of reactions take place. Heart rate increases, digestive functions decreases, skeletal muscles contract, eyes dilate, blood flow increase, hair stands on end. This reaction helps us fight, or allows us to get out of the way fast. It most likely is a reason for the success of Homo sapiens as a species.

The average adult has about 5 million hair follicles. That’s a awful lot of goose bumps.

ENDORPHINS. Not the happy drug you’re looking for.

The human body has many mechanisms that signal that something is not right. For instance, a fever indicates the presence of a harmful pathogen, thirst is a natural response to dehydration, and feeling pain brings about an awareness that damage is occurring within the body. In turn, the body may release hormones or other molecules that help overcome the crisis.

We have known for some time that endorphins act as a natural analgesic, that is, it is a natural pain reliever.  They are considered endogenous opioids because they bind to the same cell surface receptor as do opium and morphine, and hence have similar effects. There are many myths surrounding the release of endorphins into the blood stream. Many people believe that endorphins are released when one is happy, during orgasms, even when someone smiles. The truth is, that there is NO scientific evidence supporting these claims. In fact, the level of endorphins in the blood stream has been shown to decrease during sex8.

Endorphins are released in the body in response to pain, or extraneous exercise. Simply put, they prevent someone from feeling the pain associated with tissue damage. β-endorphin is a 31-amino-acid-peptide that functions as a neurotransmitter, that is, its target cell is a neuron. β-endorphin is released from the anterior pituitary gland in response to a pain signal that has been sent to the hypothalamus.  It then enters the blood stream.

Let’s first look at the pain signal. There are pain receptors throughout the body, called nociceptors. When tissues are damaged, they release a variety of substances, such as histamine, potassium and arachidonic acid. These substances stimulate the nerves and cause the release of Substance-P, which activates the pain pathway and transmits the pain signal to the central nervous system. In this way, the brain not only recognizes pain, but it also commits its source to memory. It is this recognition that creates the reflex to move away from the source of the pain.

endorphin

The opiate receptor is located on the neurons that release Substance-P. When β-endorphin is release in response to pain, it will bind to this receptor and as a result Substance-P will not be released. Therefore, the pain pathway will not be initiated, or will be reduced. β-endorphin is quickly degraded by an enzyme, and the receptor will then be free to bind to its substrate again. If this degradation process did not take place, then the feeling of pain will be nullified and the hand that inadvertently sat on the hot stove will remain there.

Addiction to opioids such as morphine and opium is the result of the drugs remaining on the receptors for long periods of time. A person becomes numb after a while because the receptors become “down regulated,” that is, there are less of them on the surface of the cell. Quite simply, there are fewer receptors and it takes more of the drug to find them. It then takes more of the drug to reach the same level of the “pain free” high.

The physiological role of endorphins in the human body has not yet been fully elucidated. However, one thing is clear. Its role is not to induce happiness, but to remove the pain.