The Anatomy of a Kiss

Most people think about what to do when kissing another person, but fewer ponder all the technical details behind it. No matter who you're kissing or why, the basic kiss relies heavily on one muscle - the orbicularis oris, which runs around the outside of your mouth. Your orbicularis oris changes the shape of your mouth while you talk, and it puckers your lips when you kiss.

But orbicularis oris is really just the tip of the iceberg. About two-thirds of people tip their heads to the right while kissing. Scientists believe this preference starts before we're born, when we tip our heads to the right in the womb. So muscles in your head, neck and shoulders tilt your head so your nose doesn't collide with your partner's nose.

In addition, the rest of the muscles in your face and head also play a part in a more involved kiss. For example:

• Several muscles move your lips around. Zygomaticus major, zygomaticus minor and levator labii superioris pull your upper lip and the corners of your mouth upward. Depressor labii inferioris and depressor anguli oris pull the corners of your mouth and your lower lip downward.
• If you open your mouth, your lateral pterygoid pulls your jawbone down. Your massiter, temporalis and medial pterygoid close your mouth.
• Several muscles - your genioglossus, styloglossus, palatoglossus and hyoglossus - move your tongue if you decide to use it.

Kissing the Blarney Stone Tourists visiting Ireland often stop by Blarney Castle near Cork to kiss the Blarney Stone. It's said that kissing the stone bestows the kisser with the gift of blarney, or eloquence. Kissing the Blarney Stone takes a lot more than just lips. To reach it, people have to lie on their backs, hold a set of handrails and tip their heads backwards until they are essentially upside down.

Anyone who has ever been kissed knows that the sensations involved aren't confined to the mouth. Your facial nerve carries impulses between your brain and the muscles and skin in your face and tongue. While you kiss, it carries messages from your lips, tongue and face to your brain to tell it what's going on. Your brain responds by ordering your body to produce:

• Oxytocin, which helps people develop feelings of attachment, devotion and affection for one another
• Dopamine, which plays a role in the brain's processing of emotions, pleasure and pain
• Serotonin, which affects a person's mood and feelings
• Adrenaline, which increases heart rate and plays a role in your body's fight-or-flight response

When you kiss, these hormones and neurotransmitters rush through your body. Along with natural endorphins, they produce the euphoria most people feel during a good kiss. In addition, your heart rate increases and your blood vessels dilate, so your whole body receives more oxygen than it does when you're just standing around. You can also smell the person you're kissing, and researchers have demonstrated a connection between smells and emotions.

Your body may also play a role in who you prefer to kiss. Researchers have proven that women prefer men with immune system proteins that are different from their own. In theory, having a baby with someone with different immune proteins can lead to healthier offspring. Scientists believe that a woman may be able to smell these proteins while kissing, and that what she smells may affect whether she finds her partner attractive.

Check out the links on the next page for more on kissing, the human body and related topics.

Cooties from Kissing? Most people know that mouths are germy places. Kissing is directly tied to a few illnesses: Mononucleosis is often called "the kissing disease" because it is carried in saliva and can be spread through kissing. The herpes simplex 1 virus causes cold sores and is easily transmitted through kissing. Although kissing doesn't necessarily cause meningitis, researchers have tracked a correlation between teenagers' number of kissing partners and likelihood of developing the disease. Some researchers theorize that bacteria that cause gastric ulcers may spread through kissing. It's unlikely that a person will contract the human immunodeficiency virus (HIV) through kissing, but the United States Centers for Disease Control has reported one case of HIV transmission contracted this way.