Trigeminal nerve

Trigeminal nerve

Johann Friedrich Meckel made the first description of the subarachnoid space investing the trigeminal nerve into the middle fossa.

Possible pathways for facial pain include: trigeminal nerve (portio major as well as portio minor (motor root).

Supratentorial sensory perception, including facial pain, is subserved by the trigeminal nerve, in particular, by the branches of its ophthalmic nerve, which provide an extensive innervation of the dura mater and of the major brain blood vessels. In addition, contrary to previous assumptions, studies on awake patients during surgery have demonstrated that the mechanical stimulation of the pia mater and small cerebral vessels can also produce pain. The trigeminovascular system, located at the interface between the nervous and vascular systems, is therefore perfectly positioned to detect sensory inputs and influence blood flow regulation. Despite the fact that it remains only partially understood, the trigeminovascular system is most probably involved in several pathologies, including very frequent ones such as migraine, or other severe conditions, such as subarachnoid hemorrhage. The incomplete knowledge about the exact roles of the trigeminal system in headacheblood flow regulationBlood-brain Barrier Permeability, and trigemino-cardiac reflex warrants for an increased investigation of the anatomy and physiology of the trigeminal system 1).

The trigeminal nerve complex is a very important and somewhat unique component of the nervous system. It is responsible for the sensory signals that arise from the most part of the facemouthnosemeninges, and facial muscles, and also for the motor commands carried to the masticatory muscles. These signals travel through a very complex set of structures: dermal receptors, trigeminal branches, Gasserian ganglion, central nuclei, and thalamus, finally reaching the cerebral cortex. Other neural structures participate, directly or indirectly, in the transmission and modulation of the signals, especially the nociceptive ones; these include vagus nervesphenopalatine ganglion, occipital nerves, cervical spinal cord, periaqueductal gray matter, hypothalamus, and motor cortex. But not all stimuli transmitted through the trigeminal system are perceivable. There is a constant selection and modulation of the signals, with either suppression or potentiation of the impulses. As a result, either normal sensory perceptions are elicited or erratic painful sensations are created 2).

Originating in the posterior fossa of the brain stem, it follows a long and complex course towards its distribution territory, crossing several regions with a complex anatomy and establishing important relationships with several structures.

The nerve fibers originate in the brainstem and are part of several grey matter nuclei occupying all the brainstem and even the first spinal cervical segments.

Each of these sensitive and motor nuclei represents different processing centers, and there is a true systematization of the information this nervous tract is responsible for conducting.

The sensitive nucleus is the largest, comprising 3 true sub-nuclei, each responsible for each aspect of the general sensitivity. The highest is the mesencephalic nucleus, located in the tegmentum close to the midline and to the grey matter close to the Sylvian aqueduct. The neurons that form this nucleus are in charge of the propioceptive integration in the Vth nerve territory, high level information for correct mastication. The main nucleus is in the pons, it is also situated in the depth of the tegmentum, and is responsible for the tactile integration of the territory of this nerve. Finally, the inferior nucleus occupies the tegmentum of the medulla, extending caudally to the first segments of the cervical spine, and is in charge of thermal and pain information. Its location explains the possible appearance of symptoms in the facial territory in patients with a degenerative/inflammatory disorder of the upper cervical spine. There is one single motor nucleus, located in the pons tegmentum supplying mastication muscles, and is correspondingly called mastication nucleus. The fibers related with all these nuclei gather in the pons and emerge through the lateral sector of its anterior aspect, forming a thick nervous tract with two roots: a thicker and lateral sensitive root and a thinner more medial motor root.

The only intra-axial segment of the Vth ends there and initiates its long course to its distribution territory; it is formed by different sub-segments before dividing itself into its terminal branches (the cisternal and Gasserian or transdural segments).

The point where the roots emerge in the brainstem is called “REZ” (Root Entry Zone), an anatomical landmark of great functional hierarchy.

see Trigeminal nerve cisternal portion.

The trigeminal nerve as the name indicates is composed of three large branches. They are the ophthalmic nerve (V1, sensory), maxillary nerve (V2, sensory), and mandibular nerve (V3, motor and sensory) branches. The large sensory root and smaller motor root leave the brainstem at the mid-lateral surface of pons.

The trigeminal nerve (the fifth cranial nerve, or simply CN V) is a nerve responsible for sensation in the face and certain motor functions such as biting and chewing. It is the largest of the cranial nerves. Its name (“trigeminal” = tri- or three, and -geminus or twin, or thrice twinned) derives from the fact that each trigeminal nerve, one on each side of the pons, has three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory. The mandibular nerve has both cutaneous and motor functions.

Sensory information from the face and body is processed by parallel pathways in the central nervous system. The motor division of the trigeminal nerve is derived from the basal plate of the embryonic pons, while the sensory division originates from the cranial neural crest.

see Trigeminal nerve sensory pathways.

Trigeminal nerve-related pathology.

see Trigeminal nerve imaging.


Terrier LM, Hadjikhani N, Velut S, Magnain C, Amelot A, Bernard F, Zöllei L, Destrieux C. The trigeminal system: The meningovascular complex- A review. J Anat. 2021 Feb 18. doi: 10.1111/joa.13413. Epub ahead of print. PMID: 33604906.

Goellner E, Rocha CE. Anatomy of Trigeminal Neuromodulation Targets: From Periphery to the Brain. Prog Neurol Surg. 2020 Oct 6;35:1-17. doi: 10.1159/000511257. Epub ahead of print. PMID: 33022684.

Dorsal root ganglion

Dorsal root ganglion

A posterior root ganglion (or spinal ganglion) (also known as a dorsal root ganglion), is a cluster of nerve cell bodies (a ganglion) in a posterior root of a spinal nerve.

This structure is critical in the processing of the pain signal from the peripheral nervous system to its position in the central nervous system.

1st order neuron: small, finely myelinated afferents; soma in dorsal root ganglion (no synapse). Enter cord at dorsolateral tract (zone of Lissauer). Synapse: substantia gelatinosa (Rexed II).

The dorsal root ganglion (sensory) is also located in the foramen within the nerve root sheath.

In the “STIR” image the dorsal root ganglion may enhance on fat suppression images.

In extreme lateral lumbar disc herniation pain tends to be more severe (may be due to the fact that the dorsal root ganglion may be compressed directly) and often has more of a burning dysesthetic quality.

Compression of the dorsal root ganglion may result in a slower recovery from discectomy and overall less satisfying outcome than with the more commonplace paramedian disc herniation.

In a study, Sanz et al. identified a metalloproteinase-dependent mechanism necessary to promote growth in embryonic dorsal root ganglion cells (DRGs). Treatment of embryonic DRG neurons with pan-metalloproteinase inhibitors, tissue inhibitor of metalloproteinase-3, or an inhibitor of ADAM Metallopeptidase Domain 10 (ADAM10) reduces outgrowth from DRG neurons indicating that metalloproteinase activity is important for outgrowth.

The IgLON family members Neurotrimin (NTM) and Limbic System-Associated Membrane Protein (LSAMP) were identified as ADAM10 substrates that are shed from the cell surface of Dorsal root ganglion (DRG) neurons. Overexpression of LSAMP and NTM suppresses outgrowth from DRG neurons. Furthermore, LSAMP loss of function decreases the outgrowth sensitivity to an ADAM10 inhibitor. Together this findings support a role for ADAM-dependent shedding of cell surface LSAMP in promoting outgrowth from DRG neurons 1).

Dorsal root ganglion (DRG) are promising sites for recording sensory activity. Current technologies for DRG recording are stiff and typically do not have sufficient site density for high-fidelity neural data techniques.

In acute experiments, Sperry et al. demonstrated single-unit neural recordings in sacral DRG of anesthetized felines using a 4.5 µm-thick, high-density flexible polyimide microelectrode array with 60 sites and 30-40 µm site spacing. They delivered arrays into DRG with ultrananocrystalline diamond shuttles designed for high stiffness affording a smaller footprint. They recorded neural activity during sensory activation, including cutaneous brushing and bladder filling, as well as during electrical stimulation of the pudendal nerve and anal sphincter. They used a specialized neural signal analysis software to sort densely-packed neural signals.

They successfully delivered arrays in five of six experiments and recorded single-unit sensory activity in four experiments. The median neural signal amplitude was 55 μV peak-to-peak and the maximum unique units recorded at one array position was 260, with 157 driven by sensory or electrical stimulation. In one experiment, they used the neural analysis software to track eight sorted single units as the array was retracted ~500 μm.

This study is the first demonstration of ultrathin, flexible, high-density electronics delivered into DRG, with capabilities for recording and tracking sensory information that is a significant improvement over conventional DRG interfaces 2).

C2 root ganglion.

Sacral dorsal root ganglion.

Dorsal root ganglion stimulation.


Sanz RL, Ferraro GB, Girouard MP, Fournier AE. Ectodomain shedding of Limbic System-Associated Membrane Protein (LSAMP) by ADAM Metallopeptidases promotes neurite outgrowth in DRG neurons. Sci Rep. 2017 Aug 11;7(1):7961. doi: 10.1038/s41598-017-08315-0. PubMed PMID: 28801670.

Sperry ZJ, Na K, Jun J, Madden LR, Socha A, Yoon E, Seymour J, Bruns TM. High-density neural recordings from feline sacral dorsal root ganglia with thin-film array. J Neural Eng. 2021 Feb 5. doi: 10.1088/1741-2552/abe398. Epub ahead of print. PMID: 33545709.

Transverse sigmoid sinus junction

Transverse sigmoid sinus junction

Anatomical localization remains integral to neurosurgery, particularly in the posterior fossa where neuronavigation is less reliable. There have been many attempts to define the location of the transverse- sigmoid sinus junction (TSSJ) using anatomical landmarks, to aid in the placement of the “strategic burr hole” during a retrosigmoid approach. There is a paucity of research allowing direct comparison of such techniques.

The asterion is not a strictly reliable landmark in terms of locating the underlying posterior fossa dura. Its location is very often directly over the transverse sigmoid sinus junction complex. Burr holes placed at the asterion may often open the bone directly over the sinus, leading to potential damage 1).

The asterion was located over the posterior fossa dura in 32% on the right and 25% on the left. Its position was over the transverse sinus or sigmoid sinus complex in 61% on the right and 66% on the left. The landmark was located above the transverse sigmoid sinus junction complex in 7% on the right and 9% on the left 2).

The top of the mastoid notch (TMN) is close to the transverse sigmoid sinus junction. The spatial position relationship between the TMN and the key points (the anterosuperior and inferomedial points of the transverse-sigmoid sinus junction, ASTS and IMTS) can be used as a novel method to precisely locate the sinus junction during lateral skull base craniotomy.

Forty-three dried adult skull samples (21 from males and 22 from females) were included in the study. A rectangular coordinate system on the lateral surface of the skull was defined to assist the analysis. According to sex and skull side, the data were divided into 4 groups: male&left, male&right, female&left and female&right. The distances from the ASTS and IMTS to the TMN were evaluated on the X-axis and Y-axis, symbolized as ASTS&TMN_x, ASTS&TMN_y, IMTS&TMN_x and IMTS&TMN_y.

Among the four groups, there was no significant difference in ASTS&TMN_x (p = 0.05) and ASTS&TMN_y (p = 0.3059), but there were significant differences in IMTS&TMN_x (p < 0.001) and IMTS&TMN_y (p = 0.01), and multiple comparisons indicated that there were significant differences between male&left and female&left both in IMTS&TMN_x (p = 0.0006) and in IMTS&TMN_y (p = 0.0081). In general, the ASTS was located 1.92 mm anterior to the TMN on the X-axis and 27.01 mm superior to the TMN on the Y-axis. For the male skulls, the IMTS was located 3.60 mm posterior to the TMN on the X-axis and 14.40 mm superior to the TMN on the Y-axis; for the female skulls, the IMTS was located 7.84 mm posterior to the TMN on the X-axis and 19.70 mm superior to the TMN on the Y-axis.

The TMN is a useful landmark for accurately locating the ASTS and IMTS 3).

Using high-resolution contrast-enhanced cranial computed tomography images, we constructed three-dimensional virtual cranial models. Fifty models (100 sides) were created from a retrospective sample of images performed in a New Zealand population. Ten methods of anatomical localization were applied to each model allowing qualitative and quantitative comparisons. The “key point” was defined as the point on the outer surface of the skull that directly overlaid the junction of the posterior fossa dura, transverse sinus (TS), and sigmoid sinus (SS). The proximity of each method to this “key point” was compared quantitatively, in addition to other descriptive observations. TSSJ localization methods analyzed included: (1) asterion; (2) emissary foramen; (3) Lang and Samii; (4) Day; (5) Rhoton; (6) Avci; (7) Ribas; (8) Tubbs; (9) Li; and (10) Teranishi.

Mean distance to the “key point” showed two tiers of accuracy, those <10 mm, and those >10 mm: Li (6.3 mm), Ribas (6.6 mm), Tubbs (6.8 mm), Teranishi (7.8 mm), Day (8.4 mm), emissary foramen (12.0 mm), Avci (13.0 mm), asterion (13.9 mm), Lang and Samii (15.6 mm), and Rhoton (17.4 mm). The asterion would most frequently overlie the TS (63%) and was often supratentorial (14%).

Each method has a unique profile of dura or sinus exposure. There are significant differences in the accuracy of localization of the TSSJ among anatomical localization methods 4).

Sixty-three patients, 29 male and 34 female, who would undergo retrosigmoid craniotomy admitted to Department of Neurosurgery, the First Affiliated Hospital of Xinjiang Medical Universityfrom March to October 2019 were enrolled in the study and were divided into trial group and control group according to the computer-generated random numbers. Preoperative venous computed tomographic angiography (CTA) combined with 3-dimensional computed tomography computed tomography (3D CT) was randomly given to the patients(n=32). Asterion was used for identification of the TSSJ in the controls (n=31). The main outcome measures as postoperative complications and relevant intraoperative indicators were compared.

Incision length, craniotomy time, bone window size in trial group were shorter or smaller than those of the controls, as(6.8±0.5) cm vs (8.0±1.5) cm, (37±8) min vs (45±15) min, (8.7±1.2) cm(2) vs (10.2±2.4) cm(2) respectively, with statistical significance (all P<0.05). No statistical significance was found in bleeding amount, incidence of sinus injury and cerebrospinal fluid leakage. While incidence of neck pain was lower in case group (15.63% vs 38.71%; P=0.04) and the remission time of incisional pain in case group was shorter [(6±1) d vs (9±2) d; P=0.01].

While the technique is used, the center of the keyhole should be located at transitional place of the lateral part of the occipitomastoid suture, the retromastoid ridge and the superior nuchal line. Compared with the traditional craniotomy method marked by asterion, it has great advantages in reducing incidence of postoperative complications, craniotomy time, and the remission time of incisional pain 5).


1) , 2)

Day JD, Tschabitscher M. Anatomic position of the asterion. Neurosurgery. 1998 Jan;42(1):198-9. PubMed PMID: 9442525.

Li R, Qi L, Yu X, Li K, Bao G. Mastoid notch as a landmark for localization of the transverse-sigmoid sinus junction. BMC Neurol. 2020 Mar 27;20(1):111. doi: 10.1186/s12883-020-01688-2. PMID: 32220232; PMCID: PMC7099776.

Hall S, Peter Gan YC. Anatomical localization of the transverse-sigmoid sinus junction: Comparison of existing techniques. Surg Neurol Int. 2019 Sep 27;10:186. doi: 10.25259/SNI_366_2019. PMID: 31637087; PMCID: PMC6778333.

Wu H, Li YL, Maimaitili M, Chen LX, Mamutijiang M, Bate G, Shen YS, Lyu MY, Zhu GH. [Assessment of computed tomographic angiographysinus development combined with occipitalbone marks for the location of transverse sigmoid sinus junction]. Zhonghua Yi Xue Za Zhi. 2020 Sep 8;100(33):2618-2621. Chinese. doi: 10.3760/cma.j.cn112137-20191210-02695. PMID: 32892609.
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