| Transcript |
So, all cranial nerves from a oculomotor standpoint have a supranuclear, nuclear, and infranuclear component to them. And the infranuclear pathway has both the neuromuscular junction and the muscle component. Supra - it means above. Infra - it means below. So, when we're doing the efferent pathway, we would like to know, is it a supranuclear problem, nuclear problem, or infranuclear problem? So, for example, for the 7th cranial neve, which controls your face, there is supranuclear input to your face, and it comes from the contralateral cortex. And so, an upper motor neuron 7th nerve paresis will involve just the lower face because the contralateral cortex supplying the upper face. Because we have bilateral innervation to the upper and lower face, a lower motor neuron 7 will cause the entire face to be out on that side. And the reason that's important is, if we just have a lower face, that is actually upper motor neuron, and that is counter-intuitive, that a lower facial nerve palsy would be upper motor neuron - and that's because of preservation of the forehead. So, if I ask a resident in a patient who has what looks like a 7th on the left, and the left face is weak, if the question is, "Is the problem on the right side, the left side, either, or neither, or both?", you cannot tell by just the 7th nerve paresis, whether it is right side or left side. We need to know if it's the lower face, upper face, or both in order to answer the question, "Is it right side, left, either, neither, or both?". However, in a lower face paralysis with sparing of the upper face, we know that is upper motor neuron, so in that case, a left cranial nerve 7 palsy, that is upper motor neuron, is actually a problem of the right side. So just like other cranial nerves, 7 has innervation from supranuclear input, and so if just put in the 3rd nerve here, the 3rd nerve has a nucleus in the midbrain, it's got a peripheral nerve, it's connected to the neuromuscular junction, and to the muscle, but there's supranuclear input that controls the 3rd, that tells the 3rd nerve to do voluntary eye movements. However, we can also talk to the nucleus with the vestibular ocular reflex, the doll's head maneuver, that does not require any supranuclear input, and so we can use the doll's head maneuver to determine whether we have the a supranuclear palsy, a nuclear, or infranuclear palsy, using the vestibular ocular reflex, the doll's head maneuver. So, as a structure, if in general, you think about supranuclear, nuclear, and infranuclear, then you will help yourself in terms of localization, and the doll's head maneuver is what we're going to be using to differentiate the supranuclear palsies. Once it becomes a 3rd nerve palsy, then you only have to decide, "Is it nuclear, fascicle (the part in the brain stem) or the peripheral nerve?" And the same can be said for 4th and 6th nerve, Supranuclear, nuclear, infranuclear: always have a system. And starting off with "Could it be supranuclear?" Alright now… |
