Somatic Afferent and Visceral Afferent Cranial Nerve Components

Due to these recent findings on the embryological derivation of these cranial nerve components, their former classification into four separate categories of SVA (I the terminal nerve, and the components of VII, IX, and X for taste sensation), SSA (VlII), GSA (V, VII, IX, and X), and GVA (IX and X) can be revised (Table III). Since the bipolar sensory neurons for all these nerves are derived from the same embryonic source (i.e., neural crest and/or placodes), the "special" versus "general" distinction is not warrented. We are thus left with the resolution of classifying most of the cranial nerve sensory components (i.e., the traditional GSA and SSA components plus I and the terminal nerve) simply as somatic afferent (SA). Due to the derivation of the receptor cells from endoderm, the taste components of VII, IX, and X are assigned to the simple category of visceral afferent (VA). The remaining sensory category of GVA for innervation of the thoracic and abdominal viscera and pharyngeal region by the vagus nerve and of the tongue and pharyngeal region by the glossopharyngeal nerve can likewise be revised to the VA category.

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