Warning: Read when sober and after sufficient ingestion of caffeine! The action of the extraocular muscles often causes considerable confusion, this is because people get confused between the anatomical action (where the action of each muscle is considered independently) and how the muscle is clinically tested (where one often has to take into account more than one muscle moving the eye).
In this post, I will be discussing the neuroanatomical differentiation between an upper motor neuron (UMN) and lower motor neuron (LMN) facial palsy. The two pathologies in the title could also be differentiated in other ways, for example, the speed of onset, additional symptoms and signs, etc.; however understanding the neuroanatomy in the context of the clinical picture, is the best way of avoiding making a grave error.
The aim of this post is to clarify some basic neuroanatomy terms and to give you a sound foundation. Before we start, a quick bit of housekeeping, I use the British spelling for neurone (also used by Gray's Anatomy, The Anatomical basis of clinical practice) as opposed to the American spelling neuron. Abbreviations used include CNS: central nervous system, PNS: peripheral nervous system, SNS: sympathetic nervous system and PSNS: parasympathetic nervous system.
I often get asked if I have any tips on how to study anatomy, so I thought a post would be the right place to express my views on this. There are lots of books on this subject, but I'm guessing you have more time to read a blog post than an entire book. With that said, I enjoy studying and teaching anatomy and have developed my own strategies based on the following principles:
Yes, I know, what a catchy title! Trust me this post says what it does on the tin. I came across these rules when I was a medical student (the days when using a tablet meant chiselling into stone) from Robert Whitaker's book Instant Anatomy, a superb book which I thoroughly recommend. Essentially the innervation of the muscles of the head & neck can be broadly covered by six rules;