ATLAS OF ANATOMY OF CRANIAL NERVES FOR DENTISTRY KEY CONCEPTS AND ILLUSTRATIVE TABLES ATLAS OF ANATOMY OF CRANIAL NERVES FOR DENTISTRY KEY CONCEPTS AND ILLUSTRATIVE TABLES Introduction VII.!Facial nerve There has been an interest in anatomy since ancient VIII.!Vestibulocochlear Nerve times. The skull and its precious content have always IX.!Glossopharyngeal Nerve been some of the most fascinating and complex ana- X.!Vagus Nerve tomic elements. The head and the neck include hi- ghly specialized parts of the body. The structures con- XI.!Accessory Nerve tained in them are closely related, being packed in XII.!Hypoglossal Nerve an extremely small area. Plus, the head and neck area have an innervation that concerns the work of The cranial nerves have seven specific functional the dentist. Dentists deal with some nerves regularly; components that can be passed within them. No cra- it is, therefore, important for the dentist to know the nial nerve has all the function within it. Each cranial anatomical aspect linked with the head and neck. nerve has specific patterns responsible for receiving Anesthesia allows us to avoid any painful stimulus sensory input through the receptors or producing the during the treatment. It was the basis for this Ana- motor function’s outputs. An additional component is tomy Compendium of the Nerves, focused on the that of proprioception, which can be traced back to a ones of the oral cavity. sensory input that presents the muscles that are in- nervated by cranial nerves [1]. Cranial Nerves Motor Functions – Output Somatic Efferent: the motor innervation of the skele- There are twelve pairs of cranial nerves. Originating tal muscles developed by somitis. from the brain, they pass through some foramina of the skull and distribute to the head-neck area. The General Visceral Efferent: the motor fibers that in- cranial vagus nerve continues in the thorax and abdo- nervate smooth muscles, heart muscles, and glands. men, innervating some entrails. The cranial nerves Only four cranial nerves transmit parasympathetic are named and numbered in sequence with Roman fibers: the oculomotor, facial, glossopharyngeal and Numbers, proceeding in the craniocaudal direction. vagus nerves. Sensory Functions – Input I.!Olfactory Nerve General Somatic Afferent: the general sensation II.!Optic Nerve (touch, pressure, temperature, pain) of the skin around the front and side of the face. An example of III.!Oculomotor Nerve this function is given by the trigeminal nerve when it IV.!Trochlear Nerve covers a wide part of the skin and mucous membra- nes of the face, while the facial, glossopharyngeal V.!Trigeminal and vagus nerves cover the area of the ear. VI.!Abducens Nerve 1 General visceral afferent: composed of the fibers ganglion, located in a subdural dimple (called the that carry the general sensation of the viscera, ge- Meckel) near the apex of the petrosal part of the tem- nerally perceived as pressure and pain. poral bone. From an embryological viewpoint, the tri- geminal forms the nerve of the first pharyngeal arch, Special somatic afferent: carries the sensations co- the same origin of all the tributary muscles mentio- ming from the eye and ear. ned above. Special visceral afferent: these fibers are associa- The nerve leaves the endocranial space through the ted with the special senses of smell, carried in the oval foramen located in the middle cranial fossa olfactory nerve and taste, transmitted in the facial, (sphenoid bone) and emerges in the infratemporal glossopharyngeal and vagus nerves. fossa. Still close to the base of the skull, the main Cranial nerves and oral cavity functions trunk releases the sensory meningeal branch and so- Let's now review the main features of the nerves in me of the motor fibers, and then divides into a smal- the oral cavity: trigeminal, facial, glossopharyngeal, ler anterior branch and a larger posterior branch. vagus, accessory, hypoglossal. Ophthalmic branch TRIGEMINAL NERVE The ophthalmic nerve provides the bulb and palpe- The fifth pair of cranial nerves (V), the trigeminal ner- bral conjunctiva, the tear gland, the skin of the head ve, carries this name because it is divided into three and nose and the mucous membranes of the parana- main branches: ophthalmic (V1), maxillary (V2) sal sinuses with sensory innervation. Before entering and mandibular (V3). The latter represents the main the upper orbital fissure, it releases three terminal branch because, unlike the other two carrying only branches, the tear nerve, the frontal nerve, and the afferent fibers, it also carries efferent fibers: it is, the- nasociliary nerve. refore, due to the mandibular nerve alone that the tri- The tear branch is of great interest concerning the geminal can be called a mixed nerve. The V is also ophthalmic branch when it comes to the oral cavity. the largest of all the cranial nerves, being responsib- The tear nerve is the smallest branch of the ophthal- le for serving—with an eminently sensory role—a lar- mic division; it runs along the lateral rectum muscle ge part of the face, the dental arches and the support- distributing itself to the tear gland and the adjacent ing structures, a large part of the oral cavity and, in conjunctiva. While in the eye socket, it communica- general, of the mucous lining structures of the head. tes with the zygomatic-temporal branch of the The apparent origin of the nerve is located in the zygomatic nerve of the maxillary division of the brainstem, exactly on the anterior face of the bridge trigeminal nerve, which carries postganglionic pa- near the middle cerebellar peduncles. The large, flat- rasympathetic fibers from the pterygopalatine gan- tened sensory root is located laterally to the thin mo- glion. These parasympathetic fibers are then transmit- tor root, which is responsible for innervating the ma- ted to the tear gland through the tear nerve, thus pro- sticatory musculature, the anterior belly of the diga- viding secretomotor innervation. stric muscle, the tensor of the tympanum and that of the soft palate, as well as transporting facial nerve fibers (VII pair of cranial nerves) through the buccal nerve. Maxillary Branch The neurons that make up the sensitive fibers have The second trigeminal nerve branch, the maxillary a trophic center located at the level of the Trigeminal nerve, is only sensory and serves the skin of the side 2 of the nose, cheek, eyelids, central part of the face, nerve divides while it is in the canal to nasopharynx, tonsils, palate, maxillary sinus, gum, form a minor palatine nerve, which co- teeth and structures associated with the upper jaw. mes out to the palate through two or The nerve emerges from the cranial vault through the three homogeneous foramins serving the round foramen after passing through the back of the soft palate, the tonsil and the uvula. cavernous sinus. The nerve flows out of the round o Upper posterior nasal branches: they foramen through the pterygopalatine fossa to enter enter the nasal cavity from the foramen the floor of the orbit at the bottom of it. Here, the ner- sfenopalatino. The nasopalatino nerve ve becomes the infraorbital nerve and enters the in- emerges. fraorbital canal of the same and comes out of the in- fraorbital hole. This nerve can be anaesthetized if an • Foramina of Scarpa: the nerve nasopalatine upper arch procedure is required, including the sinus or foramina of Scarpa is a collateral branch of lift. A publication [2] has precisely evaluated the the pterygopalatine nerve; the internal branch anesthetic effectiveness of The Wand in this procedu- of division of the maxillary branch of the trigemi- re, finding excellent results. nal nerve (V pair of cranial nerves). It runs along the floor of the nasal cavity, attached to Let's see which branches it releases during its cour- the periosteum of the septum, moving from the se. back of the septum forward. It then enters the • Medium meningeal nerve: detaches before foramina of Scarpa to access the oral cavity the maxillary nerve engages in the round hole; through the incisor hole (or anterior palatine). follows the middle meningeal artery in its ramifi- Here we observe a confluence between the cations in the dura mater. two nasopalatine nerves, which, in turn, can • Zygomatic nerves: releases the zygomatic-fa- anastomize with the major palatine branch. The cial branch that provides the sensitivity of the nasopalatine nerve serves the anterior third of cheek and the zygomatic-temporal branch that the hard palate with its mucosa. It may involve innervates the side of the forehead. The fore- the gum and support structures of the inter- head side releases a branch directly to the tear chain region. The nerve block of this structure, nerve before leaving the orbit. This carries indicated in interesting mucous and periosteal postganglion parasympathetic fibers derived interventions and also in periodontal treat- from cranial nerve VII from the pterygopalatine ments at the same area. Dental pulp is not in- ganglion. volved and anesthesia is not recommended when treatment is focused on one or two ele- • Pterygopalatine nerves: they emerge near ments. [3] the homonymous ganglion. Consequences of the block of the foramina o Orbital nerve: the orbital branches enter of Scarpa the orbit to supply the periorbite and the The method is beneficial because it allows the posterior ethmoidal and sphenoidal si- anesthesia of a large portion of the palate with nus. a minimum amount of local anesthetic. At the o Greater palatine nerve: comes out from same time, it can be problematic, as the injec- the homonymous hole located in the pala- tion procedure is often painful in this area. The te about 1 cm apically to the upper mo- main anatomical finding is represented by the lars; it goes forward to the midline to ser- interincisive papilla, under whose palatal conti- ve the entire palate.