The anatomical term “commissure” refers to a junction in the anatomy, a site where two things join. A number of different structures in the body may be referred to as commissures, with some of the most important examples being located inside the brain. The complex network of communication within the brain is enabled in part by several commissures which allow different parts of the brain to communicate with each other. Without these junctions, the brain would not be able to relay information nearly as quickly.
In the case of the brain, the two halves of the brain are divided by a deep groove known as the longitudinal fissure. The corpus callosum, a bundle of nerve fibers, spans this divide to facilitate communication between the hemispheres of the brain. This structure includes the anterior commissure. The brain also contains the posterior commissure, another network of nerves which is used to bridge the space between two areas of the brain so that they can signal each other.
Likewise, the spinal cord has a structure known as the commissure which crosses between the sides of the spinal cord, creating a join. The bilateral symmetry of the body can be seen in many structures like the brain and spinal cord which come in halves even though people often think of them as solid and singular structures. Different halves have different functions, making bodily junctions important. When these junctions are severed, people can sometimes develop health problems as a result, although in structures like the brain, the remaining tissue may remap itself to compensate.
People also sometimes refer to the folds of the lips and eyes as commissures because they mark a point where two parts of the body are joining. A commissure of this nature can become a topic of interest for a physician because these folds sometimes develop irritation or attract infections, requiring treatment. Cracks and dry skin on the face, for example, often show up near the corners of the eyes and lips first.
In a surgical procedure known as a commissurotomy, the junction may be surgically severed or excised. This can be done to treat several different health issues, such as a microstomia or small mouth, which can be treated by cutting into the commissure at the corner of the lips to make the mouth wider. This procedure may be performed if someone has difficulty eating or speaking as a result of having an unusually small mouth.