| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (JP) Class of 2022, Baylor College of Medicine, Houston, Texas; (NA) Class of 2023, Baylor College of Medicine, Houston, Texas |
| Transcript |
Does everything that a cranial nerve can do. It has special motor, it has regular motor, special sensory, has regular sensory, and it does autonomic nervous system functions. So when we're dealing with VII you need to know that it does all these things so that you can interpret how this nerve actually does what it does. We already talked about the supranuclear input to the 7th nerve nucleus, and that is from the contralateral side. And the upper face is innervated bilaterally, and so with a lower motor neuron VII we have involvement of both upper and lower face. So let's just start with the nucleus of VII. Its fascicle travels dorsally for a short portion, which makes a bump in the back of the brainstem called the facial colliculus. And then the nerve travels ventrally and has exits at the root exit zone, where it's tethered at the pons. Everybody has to go through the ganglion, and the geniculate ganglion, and the motor portion exits out stylomastoid foramen. It drops off some hitch hikers to strap muscles in the neck, and in the face it travels ‘To Zanzibar By Motor Car', which is the ‘Temporal branch, the Zygomatic branch, the Buccal branch, the Mandibular, and the Cervical branch', controlling the ipsilateral facial muscles on that side. In the internal auditory canal, a small branch, which is the special motor branch, which is the nerve to stapedius. The nerve to stapedius stabilizes the stapes, and if you don't have stabilization of stapes, you might get the symptom of hyperacusis - sounds might be loud to you. There's also small sensory hitch-hiker that's right behind your ear, which is the regular sensory, posterior auricular branch. So right behind your ear is special sensory, goes right behind your ear. So we've covered the special motor, the regular motor, which was ‘To Zanzibar By Motor Car', the regular sensory, and so now we only have to deal with the autonomic fibers and the special sensory fiber. The autonomic fibers go to the glands - that includes the lacrimal gland and the submandibular and parotid glands. And the lacrimal gland branch starts as a nucleus, travels as nervus intermedius, and then the greater superficial petrosal nerve. And that eventually becomes the vidian nerve, and the lacrimal nerve to the lacrimal gland to control tearing. And so a one eye dry eye would be a symptom we might see in a 7th nerve palsy from involvement of the greater superficial petrosal nerve branch, the vidian nerve. The tongue is carried on chorda tympani. So chorda tympani carries the taste, the special sensory, to the anterior 2/3 of the tongue. And that nerve is called the lingual nerve. The hitch-hikers for the autonomics innervate the submandibular glands and the salivary glands, the minor salivary glands, as autonomic branches of VII. So in other words, VII can do everything a nerve can do. It's got special motor to the nerve to stapedius, regular motor ‘To Zanzibar By Motor Car' to the muscles of the face as well as dropping some hitch-hikers on the strap muscles of the neck, the special sensory to the anterior 2/3 of the tongue carried on the lingual nerve via chorda tympani, the regular sensory which is a hitch hiker after leaving the internal auditory canal just behind the ear to the posterior auricular nerve, and the autonomic function for tearing to the lacrimal gland via vidian and the superficial petrosal nerve, and the salivary glands in your mouth, the submandibular glands and the major and minor salivary glands. So if you just know that every nerve including VII has a nucleus, a nerve, and its branches. Everyone has to pass through the ganglion, and then you can go to the target organ. I think that you'll see you'll have a better understanding of VII by understanding its anatomy. |
