TMJ: Basic anatomy and physiology of the temporomandibular joint
The tempormandibular joint (jaw joint or TMJ) is a rather complex aspect of our anatomy. Its complexity leaves it prone to a number of pain responses and histological (tissue) changes. The following is a brief description of its anatomy and how it functions in relation to the rest of our skull and central nervous system.
The squamous portion of the temporal bone articulates with the condyle of the mandible at a juncture that is known as a temporomandibular joint (TMJ). In great apes (man included) the mandible is fused at the midline allowing each of the bilaterally symmetrical TMJ’s to operate as one unit. Together both TMJ’s are referred to as a single craniomandibular joint (CMJ). The CMJ encompasses the whole mandible along with both articulating surfaces of the temporal bone (2). The fact that the CMJ is made up of two joints that work in unison creates a dependence of one on the other. Any dysfunction experienced on one side is sure to influence the opposite side (5).
The TMJ is extremely complex and is almost constantly in motion. The TMJ is mobile when we talk, chew, make certain facial expressions; even during sleep, it is activated to some degree. It is composed of two synovial cavities that allow movement of the mandibular condyle over the glenoid fossa of the temporal bone. The superior portion of the joint is an arthrodial gliding joint and the inferior portion is a ginglymoid hinge joint (5). The complexity of the TMJ allows lateral movement, elevation, depression, protrusion, and retraction of the mandible (2). The reduction of the canines in hominids during evolution allowed us the rotary movement that is not possible in most primates. The drawback is that teeth grinding came with this trait. Branches of the trigeminal nerve innervate the muscles of mastication that are responsible for movement of the mandible. The trigeminal nerve is related to the reticular alarm system (RAS) of the central nervous system, which is active during mental stress (1, 3, 4, 5,). Trigeminal nerve innervates the pons of the brain which is where sympathetic (fight or flight) nerve responses are registered. This is one of the main reasons that mental stress is a common etiology for temporal mandibular dysfunction.
- 1) Campbell, Bernard G., Loy, James D.: Humankind Emerging, The Concise Edition. Pearson Education Company, Boston, MA; 2002.
- 2) Elson, Lawrence M., Kapit, Wynn.: The Anatomy Coloring Book, 3rd edition. Benjamin/Cummings Publishing Company Incorporated, Menlo Park, CA; 2002.
- 3) Henderson, David F., A Comprehensive Overview of the Temperomandibular Joint. 2004.
- 4) Marieb, Elaine N.: Human Anatomy and Physiology, 4th edition. Benjamin/Cummings Publishing Company, Menlo Park, CA; 1998.
- 5) Upledger, John E., D.O., F.A.A.O.: Craniosacral Therapy II, Beyond the Dura. Eastland Press Incorporated, Seattle, WA; 1987.