The chorda tympani is a facial nerve that transmits neural impulses from the tongue to the brain, where these impulses are translated into the sensation of taste. The origin of the chorda tympani nerve is a branch of one of the major facial nerves, referred to as the seventh cranial nerve. This branch occurs in the facial canal, a bony canal at the side of the skull, approximately level with the eye sockets. From the facial canal, the chorda tympani is routed via the middle ear, running from front to back along the eardrum, or tympanic membrane. Emerging from the skull into the mouth cavity, near the base of the tongue, the nerve joins up with a cluster of nerve tissue called the submandibular ganglion, and then continues into the tongue, and innervates the cells at the front of the tongue.
The main role that the chorda tympani nerve plays in the sensation of taste is to detect tastes on the front two thirds of the tongue, and to transmit the appropriate nerve impulses to the brain. This function is carried out by means of sensory fibers within the nerve. In addition to these sensory fibers, the nerve also contains fibers of a different type, which serve to stimulate the submandibular and the sublingual salivary glands, causing them to produce saliva. A further function of these stimulatory fibers is to cause blood vessels in the tongue to dilate.
Chorda tympani anatomy is connected with a number of other, related facial nerves. The mandibular nerve transmits sensations of temperature, touch, and pain from the tongue. Another nerve, the glossopharyngeal nerve, transmits sensations of taste from the back third of the tongue to the brain. The vagus nerve innervates the epiglottis.
The mammalian taste system forms a complex feedback loop. The different nerves that are involved in this system have the ability to inhibit each other, which is how a person is able to become desensitized to a strong taste. For example, if a person holds a sweet with a strong sour flavor in his or her mouth, the taste will seem less intense after a while. The chorda tympani appears to serve an important role in inhibiting the signals from the other nerves involved in the sensation of taste. Chorda tympani damage can result in a disruption of the inhibitory function, causing the sensation of taste to become erratic and uncontrolled.
