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.