Essay: The Trigeminal Nerve

The trigeminal nerve is the fifth and largest cranial nerve. The nuclei of the sensory trigeminal nerve are composed of three parts and cover the entirety of the midbrain, pons, medulla, and into the top of the cervical spinal cord. From rostral to caudal, the nuclei consist of parts in the mesencephalic nucleus, chief sensory nucleus, and spinal trigeminal nucleus. The spinal trigeminal nucleus can also be divided even further into the Pars Oralis, Pars Interpolaris, and Pars Caudalis. The sensory nucleus of the trigeminal nerve is located in the pons and is complex. The lower branch of the nucleus contains the ophthalmic division, and the upper branch is the mandibular branch. The main sensory nucleus is the large rostral head. The trigeminal nucleus also spans the spinal tract caudally. Anatomically, ventromedial to the sensory nucleus exists the motor nucleus.
The sensory trigeminal nuclei have a complex system of connectivity. The afferent signals are conceived from the ganglion cells which are on the lateral part of the ventral surface of the pons. The signal is relayed in the cerebral cortex only after the axons of the nucleus cross and rise to the thalamic nuclei. Moving downwards, the ganglion cells have to make their way through both the pons and medulla in the fifth cranial nerve spinal tract, which ends in the nuclei of the trigeminal nerve.
The main sensory nerve of the head is the trigeminal nerve. It covers most of the face functions except the jaw and auricle. The afferent and somatic system of nerves of the nose, mouth, and eyes are all through the trigeminal nerve. Also, the dura and cranial blood vessels get their sensory nerves through passing the trigeminal nerve. The peripheral axon terminals of the trigeminal nerve release vasoactive compounds which reach the cranial blood vessels through sensory nerves. This is proposed to be one of the biological reasons behind headaches.
Damage or pressure on the trigeminal nerve is thought to be the reason behind some clinical conditions and syndromes. Wallenberg syndrome depict the anatomical sophistication of the trigeminal nerve and its connections. Usually, stroke patients suffer from loss of motor function and sensation to one side of the body. In patients with Wallenberg syndrome, a stroke affects one side of the body and the annihilation of pain-temperature sensation of the face on the other side of the body. Ascending neurons of the spinothalamic tract and the spinal tract of the trigeminal nerve are neighbors. The pain-temperature input travels contralaterally in the spinothalamic tract, but from the same side in the spinal tract. A stroke destroys both tracts at the same time. This is why Wallenberg syndrome patients suffer from pain-temperature sensation in the ipsilateral face and contralateral body.
Other syndromes include trigeminal neuralgia and cluster headaches. In trigeminal neuralgia, a patient suffers from chronic pain that comes in typical and atypical types. Typically, a patient experiences severe, unexpected, shock-like pain in half of their face usually with a timespan of seconds to a few minutes. An exact cause as to why the pain happens is uncertain, but it is thought to be related to loss of myelin around the trigeminal nerve. On the other hand, a cluster headache is a neurological disorder in which patients suffer from extremely painful headaches that are around the eye on one side of the head. In addition to this, some symptoms like eye watering, congestion, and swelling arise. Again, the exact cause of the disorder is debatable, but it is usually linked to smoking and a genetic history.