Did you just feel that last warm gasp of summer air touch your face? Fair enough, whilst writing this it is still summer, but there is more to it than just motion of the air in the atmosphere. And this is where the fifth cranial nerve, or trigeminal nerve, comes in. It is a nerve responsible for such motor functions as chewing and biting and – you guessed it – the sensation in the face.
When talking about the trigeminal nerve, it is most important to remember both functional classification and anatomical division. For the sake of simplicity let’s start with the anatomy part. As the name “trigeminus” already suggests, the nerve itself is divided into three great branches – ophthalmic (or V1), maxillary (V2) and mandibular (V3), which leave the skull via different foramina – the superior orbital fissure, foramen rotundum and foramen ovale, respectively. Those branches converge on the trigeminal ganglion, from which a large sensory root and a smaller motor root travels to the brainstem, which it enters at the level of pons. This also quite precisely describes the proportion of function in the nerve, of which the most part is sensory that involves all three branches. When talking about interesting and unique things about the nerve, then the borders of the dermatomes of the branches are relatively sharp and have almost no overlap, comparing to other dermatomes of the body. This means that, when under local anesthesia or if a branch is infected, a very well-defined area will be affected. To explore the nerve in greater detail, we truly recommend you to visit anatomynext.com. The amazing detail really makes it stand out in the field and make anatomy learning and teaching a different experience.
When talking about the function, it is usually easier to learn the nerve step-by-step, starting from the very uppermost branch – the ophthalmic or V1. This branch transmits sensory information from the forehead, scalp, upper eyelids, parts of the eye such as conjunctiva and cornea, most of the nose (the exception are the nose wings, which are innerved by the maxillary branch), nose mucosa with the help of the maxillary branch and the frontal sinuses. Interestingly enough, the nerve innervates dura mater and meningeal vessels as well, although this is done in a teamwork of all three branches.
The maxillary nerve furthermore covers lower eyelids, nares and the upper lip, the cheek, upper teeth and gums, roof of the pharynx along with the palate and the sinuses that the ophthalmic branch did not cover – the maxillary, ethmoid and sphenoid ones.
The third branch, or the mandibular nerve transmits senses from the lower lip along with lower teeth and gums, the chin and the jaw and parts of the external ear. It is worth noting though that the angle of the jaw is not innerved by this branch, but by the C2-C3.
When summarizing the sensory part of trigeminal nerve, it is very useful to use sensory diagrams, which you can check out when learning anatomy with the help of Anatomy Next as well. As I already mentioned earlier, the borders are quite sharp and specific for each branch and this helps those of us who have a good visual memory, and all of the branches take part in meningeal innervation and divide the job of innervation of the sinuses between the ophthalmic nerve (for the frontal sinus) and the maxillary nerve (the ethmoid, maxillary and sphenoid).
The smaller, but not lesser part of the nerve has a motor function which involves four muscles of mastication (masseter, temporal and lateral and medial pterygoids) as well as four other muscles – tensor veli palatini, tensor timpani, mylohyoid and the anterior belly of the digastric. They are all controlled by the motor part of the mandibular branch and involved into the process of eating – biting, chewing and swallowing. The exception is the tensor tympani, which has a sound dampening function, including the sound of chewing.
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