Afferent fibers mediate sensation from posterior external auditory canal, concha, ear lobe, and deep parts of face. Degeneration Interruption of the continuity of the axon separates the distal axon from its metabolic source, the neuron or cell body. Wallerian degeneration of the distal axon and myelin sheath begins within 24 hours. Macrophages phagocytose degraded myelin and axons. Regeneration Neuron metabolism leads to increases in mRNA, enzymes, and structural proteins.
Axonal stumps swell with axoplasm and proliferation of neurofilaments.
Conditions at the site of injury govern the fate and organization of the sprouts. The presence of a peripheral facial paralysis demands a complete head and neck examination with otoscopy and cranial nerve evaluation. Unable to wrinkle forehead, raise eyebrow, wrinkle nasolabial fold, purse lips, show teeth, or completely close eye. Because of uncrossed contributions from ipsilateral supranuclear areas, movements of the frontal and upper orbicularis oculi mm. tend to be spared. Facial movement may be present on affected side during emotional expression.