ABSTRACT
We did a light and electron microscope study of the infrared receptors in the labial pits of a python, Python regius. The receptors are elongated, tapering terminal nerve masses about 8 × 20 μm located immediately below the conified surface of the pit fundus. The receptors are surrounded and supported by epithelial cells, and together with these epithelial cells are renewed and sloughed off periodically with each molting cycle. Each terminal nerve mass is packed with mitochondria in numbers not seen in any other sensory organ. Beneath the receptors is a dense network of fine capillary vessels which probably serve both to supply the tremendous energy requirements of the mitochondria-rich receptors and to stabilize and control the thermal sensitivity of the receptors. In active terminals (as opposed to degenerating ones), the mitochondria show both energized and discharged states, as well as ladder-like junctions between individual mitochondria, which suggest that the mitochondria are intimately involved in producing the nerve impulse.
