In addition to housing main parts of the nervous system — the brain and spine — and the start of the digestive system, the head contains many important sensory organs.
Major sensory organs located in the head include:
- Ears: The outer, middle, and inner ear are responsible for collecting auditory information. Sound waves travel through the ears and vibrate membranes and tiny bones. Those signals are sent to the brain via the vestibulocochlear nerve. Other than hearing, your inner ears also help you keep your balance.
- Eyes: Light rays pass through the eye and refract through the vitreous humor, or liquid part of the eye. This stimulates the optic nerve, which sends the information to the brain.
- Mouth: The mouth contains the teeth, tonsils, and tongue. There are 32 teeth in average adult’s mouth. They are used to grab, tear, chew, and grind food. Teeth also affect the shape of our mouth, facial expression, and the way we form words. Tonsils are located in the back of throat and are part of the lymphatic system. They catch and kill germs that enter the body through the mouth. Tonsillitis is a fairly common infection of the tonsils. This is first treated with antibiotics but can require surgical removal of the tonsils, called tonsillectomy. The tongue is covered in taste buds, which collect tastes. Three nerves (facial, glossopharyngeal, and vagus) then send this taste information to the brain where it is interpreted. The tongue also helps you speak; its movement inside the mouth helps form sounds that become words.
- Nose: Olfactory nerves in your upper nasal cavity send messages to your brain to help you distinguish an infinite number of smells. The sense of smell also aids your sense taste.
Facial expressions, created by muscles that crisscross throughout the head, play a big role in how we express ourselves. Research in the 1960s by Paul Ekman showed that there are some universal facial expressions, meaning that people across the world understand these expressions the same way. These include fear, anger, disgust, joy, and surprise. Other emotions are open to cultural and personal interpretation.
The skin of the head is different than skin of other areas of the body. It sees more exposure to the elements than most other parts of the body. Also, skin in certain areas of the head is thinner and more sensitive, especially the skin around the eyes.