Trigeminal Nerve - Peripheral Anatomy

Peripheral Anatomy

The three major branches of the trigeminal nerve, the ophthalmic nerve (V₁), the maxillary nerve (V₂), and the mandibular nerve (V₃) converge on the trigeminal ganglion (also called the semilunar ganglion or gasserian ganglion), located within Meckel's cave, and contains the cell bodies of incoming sensory nerve fibers. The trigeminal ganglion is analogous to the dorsal root ganglia of the spinal cord, which contain the cell bodies of incoming sensory fibers from the rest of the body.

From the trigeminal ganglion, a single large sensory root enters the brainstem at the level of the pons. Immediately adjacent to the sensory root, a smaller motor root emerges from the pons at the same level.

Motor fibers pass through the trigeminal ganglion on their way to peripheral muscles, but their cell bodies are located in the nucleus of the fifth nerve, deep within the pons.

The areas of cutaneous distribution (dermatomes) of the three branches of the trigeminal nerve have sharp borders with relatively little overlap (unlike dermatomes in the rest of the body, which show considerable overlap). Injection of local anesthetics such as lidocaine results in the complete loss of sensation from well-defined areas of the face and mouth. For example, the teeth on one side of the jaw can be numbed by injecting the mandibular nerve. Occasionally, injury or disease processes, though, may affect two or all three branches of the trigeminal nerve, and in these cases the involved branches may be termed:

• V1/V2 distribution - referring to the ophthalmic and maxillary branches
• V2/V3 distribution - referring to the maxillary and mandibular branches
• V1-V3 distribution - referring to all three branches

Notably, nerves on the left side of the jaw outnumber slightly the number of nerves on the right side of the jaw.