The maxillary nerve is the second branch of the trigeminal nerve, which originates embryologically from the first pharyngeal arch. It is primarily responsible for providing sensory input to the mid-third of the face. In this article, we will explore the anatomy of the maxillary nerve and its sensory and parasympathetic functions.
The trigeminal nerve is composed of four nuclei that extend from the midbrain to the medulla. These nuclei include the mesencephalic nucleus, the principal sensory nucleus, the spinal nucleus, and the motor nucleus. At the level of the pons, the sensory nuclei combine to form a sensory root, while the motor nucleus continues onward to form a separate motor root. This division of the trigeminal nerve is analogous to the division of the dorsal and ventral roots of the spinal cord.
Within the middle cranial fossa, the sensory root expands into the trigeminal ganglion, which is a collection of nerve cell bodies located outside the central nervous system. It is located lateral to the cavernous sinus, in a depression of the temporal bone known as the trigeminal cave or Meckel’s cave. The motor root passes inferiorly through the floor of the trigeminal cave, and supplies motor fibers only to the mandibular division (V3).
From the trigeminal ganglion, the three terminal divisions of the trigeminal nerve arise; the ophthalmic (V1), maxillary (V2), and mandibular (V3) nerves. The maxillary nerve passes through the lateral wall of the cavernous sinus before exiting the skull through the foramen rotundum. This nerve branch also gives rise to numerous sensory branches, which include the superior alveolar nerves (anterior, posterior, and middle), the middle meningeal nerve, the infraorbital nerve, the zygomatic nerve, the inferior palpebral nerve, the superior labial nerve, the pharyngeal nerve, the greater and lesser palatine nerves, and the nasopalatine nerve.
The maxillary nerve’s terminal branches innervate the skin, mucous membranes, and sinuses of derivatives of the maxillary prominence of the 1st pharyngeal arch. This includes the lower eyelid and its conjunctiva, the inferior posterior portion of the nasal cavity (the superior anterior portion is serviced by CNV1), the cheeks and maxillary sinus, the lateral nose, the upper lip, teeth, and gingiva, as well as the superior palate.
Postganglionic fibers from the pterygopalatine ganglion (which originates from the facial nerve) travel with the maxillary nerve to service the lacrimal gland and mucous glands.
The maxillary nerve is a branch of the fifth cranial nerve, or the trigeminal nerve. This nerve is made up of both motor and sensory roots, and it has three main branches: the ophthalmic, the maxillary, and the mandibular. It is formed from sensory nuclei in the midbrain and the motor root of the trigeminal ganglion in the pons. The maxillary nerve gives rise to numerous sensory branches, such as the superior alveolar nerve (which is composed of an anterior, posterior, and middle branch), the middle meningeal nerve, the infraorbital nerve, the zygomatic nerve, the inferior palpebral nerve, the superior labial nerve, the pharyngeal nerve, and the greater and lesser palatine nerves. Additionally, it gives rise to the nasopalatine nerve.
The maxillary nerve's sensory function is to innervate the skin, mucous membranes, and sinuses of derivatives of the maxillary prominence of the first pharyngeal arch. This includes the lower eyelid (and its conjunctiva), the inferior posterior portion of the nasal cavity (with the superior anterior portion being innervated by the trigeminal nerve's CNV1), the cheeks, the maxillary sinus, the lateral nose, the upper lip, the teeth, the gingiva, and the superior palate.
The maxillary nerve also serves a parasympathetic function by having post-ganglionic fibres from the pterygopalatine ganglion travel with it to the lacrimal gland and the mucous glands of the nasal mucosa.
Trigeminal neuralgia is a disorder characterized by chronic pain within the trigeminal nerve's distribution in the face. This is an example of neuropathic pain, and damage to the nerves can cause hyperalgesia (increased sensitivity to pain) and allodynia (pain from a usually non-painful stimulus). Light touch can often trigger excruciating episodes of pain, and its cause is unknown. It is thought to be the result of nerve damage due to conditions such as multiple sclerosis, stroke, and trauma.
The pain is usually unresponsive to typical analgesics, including opioids. As a result, anticonvulsants such as carbamazepine are used to reduce nervous transmission of the pain. This works by blocking the active voltage-gated sodium channels. When pharmacological agents don’t work, surgical destruction of the nerve is possible. However, this causes loss of sensation in the affected area of the face.
The anatomy of the maxillary nerve is important to understand for diagnosis and management of trigeminal neuralgia. With this knowledge, clinicians can select the best course of treatment for this disorder.
