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The following paper deals with several less well known features of the human cranial nerves. It is apparent that there are several design faults, but I was not consulted at the time of design! The Canadian Economist John Kenneth Galbraith in his book The Affluent Society coined the expression "the conventional wisdom" and went on to remark that conventional wisdoms lagged behind development. While writing Clinical History and Examination Taking , 1 I realised that this comment also applied to much conventional clinical teaching.
Most doctors claim to have 12 cranial nerves, whereas humans in fact have 24 (12 pairs). However, on semantic grounds, we probably have 26. The name "olfactory nerve" presupposes smell, a perception of an airborne chemical stimulus that reaches consciousness. Pheromones are not smelt and thus, on semantic grounds, cannot be described as being detectable using olfactory mechanisms. Although humans are said not to have a specific "pheromone nerve", some part of the olfactory apparatus could fulfil the function of the vomeronasal nerve (nerve 0) as present in other vertebrates, 2 but not, strictly speaking, in humans.
OPTIC NERVES
Contrary to the conventional wisdom, the optic nerves are not purely sensory nerves. At least 20% of the fibres are efferent and serve to continuously programme the computer peripheral that is the retina. Indeed, certain visual patterns are analysed locally in the retinal nerve complexes before transmission back to the brain. 3
The conventional wisdom is that we see a scene as if it were a photograph. In fact, we only see "completely" the portion that falls in the macular region, which is only a small proportion of a scene. The further away from the macula that parts of a scene are focused, the less information is derived. The proof of this? The area of a visual field decreases when the peripheries of a visual field are identified with a small non-moving object, compared with the field obtained when using a small moving object. The area becomes even smaller if a small number is used as the object and the number has to be identified (fig 1). Thus, we all have tunnel vision in terms of accuracy. Despite this, we have a strong subjective illusion of a seamless, detailed reality all around...