The 11th century translations Premnon physicon by Alfanus of Salerno and Pantegni by Constantine the African offered to the Latin West two systematic descriptions of the human bodily architecture and its functioning. Both works highlight the relationship between the material constitution and teleological principles at play in the living body. This paper explores the working of one of these principles, the ‘animal power’, and its principal organ, the brain, within the living body. In particular, it examines the account of pain within these systems, underscoring its relationship to sensation: pain is conceived as an affection of the soul, and as a physical-material change in the sense organ, which is connected with the brain in its activity.