Sensory Fields and Properties of the Oesophageal Proprioceptors in the Mollusc, Philine

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Abstract
The buccal ganglia of Philine each contain four mechanosensory neurones that are proprioceptors in the oesophageal wall. The sensory fields of the three small receptors are bilateral and separate from each other, but two are overlapped by the more extensive field of the largest cell. The sensory field of each receptor overlaps that of its contralateral homologue. The receptors respond to touch or stretch of the oesophageal wall or certain nerve trunks with a rapid burst of impulses, which adapt quickly to repetitive stimulation. The soma spike is characterized by a large undershoot that summates at high-impulse frequencies to hyperpolarize the cell. Repetitive stimulation leads to the axon spike failing to propagate to the soma. Blocking most probably occurs at a branch point on the main axon within the ganglion. Impulses generated in one part of the axon normally propagate to all parts of the cell. Conduction velocity increases in the axon as the soma is approached. Conduction velocity may vary in different branches of the axon.