The inferior alveolar nerve is found in the mandible and contains sensitive fibers responsible for the teeth, chin, and lower lip. In addition, the inferior alveolar nerve includes a motor branch that controls the mylohyoid muscle and the digastric muscle. Dentistry uses the nerve pathway in part for local anesthesia (conduction anesthesia).
What is the inferior alveolar nerve?
The inferior alveolar nerve is a branch of the mandibular nerve that begins at the trigeminal nerve, the 5th cranial nerve. The semilunar ganglion switches fibers to postganglionic neurons. This nerve cord, as the mandibular nerve, exits the cranial cavity through the oval opening (foramen ovale) and reaches the subparietal fossa (fossa infratemporalis), which is located in the neighborhood of the greater sphenoid wing (ala major ossis sphenoidalis). Several branches of the mandibular nerve branch off at this point, including the inferior alveolar nerve. It belongs to the peripheral nerves and consists of both sensory nerve fibers, which transmit information such as pressure and pain to the brain, and motor nerve fibers, which control muscles. The inferior alveolar nerve is identical to the alveolar nerve of the mandible.
Anatomy and structure
The inferior alveolar nerve has four branches. One of these, the mylohyoid nerve, supplies both the mylohyoid and digastric muscles with commands to control movement. The rami dentales or dental branches lead to the roots of the teeth. In addition, fibers from this branch participate in the inferior dental plexus. The remaining nerve tracts of this plexus originate from the rami gingivales inferiores, which extend from the dental plexus inferior to the gums (gingiva). The third branch of the inferior alveolar nerve is the incisive ramus, which also consists of sensory nerve fibers and innervates the anterior teeth. The inferior alveolar nerve begins at the mandibular nerve and passes under the external wing muscle (lateral pterygoid muscle). This muscle is supplied by another branch of the mandibular nerve – namely the lateral pterygoid nerve. The inferior alveolar nerve then moves to the mandibular foramen and shortly thereafter enters the mandibular canal (canalis mandibulae). Its course finally leads the inferior aveolar nerve to the mental foramen. As a fourth branch, the mental nerve branches off there from the inferior alveolar nerve. It is also known as the chin nerve and extends to the lower lip.
Function and tasks
The inferior alveolar nerve is a mixed nerve with motor and sensory fibers. The latter make up the larger portion, as they divide into three branches of the nerve, whereas only one branch of the inferior alveolar nerve is responsible for muscle control. The motor branch is the mylohyoid nerve. It controls the mylohyoid muscle, which is also called the mandibular hyoid muscle in German. The muscle participates in the opening of the mouth on the one hand and in swallowing on the other. In addition, it forms a large part of the floor of the mouth. The digastric muscle also depends on the neural supply from the mylohyoid nerve. The digastric muscle has two bellies and also participates in opening the mouth and swallowing. In this process, the facial nerve also supplies part of the muscle. The sensitive branches of the inferior alveolar nerve transmit irritation from the roots of the teeth, the gums and the lower lip to the central nervous system. The rami dentales are responsible for the posterior teeth. The third branch of the inferior alveolar nerve is the incisive ramus. Like the rami dentales, it is responsible for carrying somatosensitive information from the teeth – but unlike the rami dentales, the ramus incisivus is responsible for the incisors (dentes incisivi) and the canine (dens caninus) of the corresponding side of the body. The fourth and last branch of the inferior alveolar nerve is embodied by the mental nerve, which also has several branches. With them, the nerve reaches the lower lip and receives information such as pressure, vibration, touch, pain and temperature. In this case, the sensations originate from both the skin of the lower lip and the mucosa.
Diseases
In dentistry, the inferior alveolar nerve serves as one of several ways to provide local anesthesia. To do this, the dentist injects an appropriate medication that causes temporary loss of the nerve. The sensitive nerve pathways can now no longer transmit signals – and the patient accordingly feels no pain when the dentist works on the teeth. This type of anesthesia is known as conduction anesthesia. An involuntary loss of the inferior alveolar nerve is possible, for example, after an injury. In this case, numbness of the tissue is also possible. This condition is called paresthesia in medicine. Paresthesia may also manifest as tingling, falling asleep, or disturbance in the perception of heat and cold. As a result of a lesion of the inferior alveolar nerve, difficulty opening the jaw and difficulty swallowing are possible. More common than damage affecting only the inferior alveolar nerve are neurological problems at a higher level, for example in the mandibular nerve or the trigeminal nerve. In addition to injury, the many possible causes include tumors, inflammation, hemorrhage, contusions, and neurodegenerative diseases affecting the sensitive nuclei in the brainstem.
