Stationary and non-stationary occurrences of miniature end plate potentials are well described as stationary and non-stationary Poisson processes in the mollusc Navanax inermis

Neuronal analysis of pharyngeal peristalsis in the gastropod Navanax in terms of identified motoneurons innervating identified muscle bands. II. Radial and circumferential motor fields

The neuronal basis of pharyngeal ingestion and peristalsis was studied in the gastropod Navanax inermis. Radially and circumferentially oriented muscles produce expansion and constriction of the pharynx. Motor fields of 11 identified radial motoneurons and 13 identified circumferential motoneurons were determined with respect to circumferential and longitudinal muscle band coordinates by muscle movements, electromyography, antidromic stimulation and axonal anatomy. Activation of these identified motoneurons can account for all the elemental pharyngeal movements observed during feeding. Four motoneurons, each innervating most of radial muscle, can mediate ingestion. Three radial motoneurons with anterior motor fields can mediate anterior expansion during sealing of the pharyngeal lips around prey and during regurgitation. Ten circumferential motoneurons have small arciform motor fields, the distributions of which correspond to the regional specializations in circumferential band organization. Arciform constriction can center eccentric ingested prey within the pharyngeal lumen during peristalsis. Arciform constrictions could combine to form an annular constriction in peristalsis. Small, non-overlapping, circumferential motor fields maximize the number of independent annular units available to produce a fine peristaltic wave. Sphincters have more circumferential motoneurons with smaller motor fields; this innervation permits finer motor control. Radial motoneurons with posterior motor fields can produce expansion caudal to a circumferential constriction during peristalsis. Motor fields of regional radial motoneurons show greater interanimal variability than circumferential motor fields, which is correlated with a less essential role of radial motoneurons in peristalsis. Two circumferential motoneurons with giant posterior pharyngeal motor fields can mediate pharyngeal emptying either in swallowing or in regurgitation.

Neuronal analysis of pharyngeal peristalsis in the gastropod Navanax in terms of identified motoneurons innervating identified muscle bands. I. Muscle band identifiability

The neuronal basis of pharyngeal ingestion and swallowing can be conveniently studied in the marine mollusc Navanax inermis because of the small number of neurons involved in the behavior, reproducible identifiability of many individual neurons and simple muscle arrangement. The Navanax pharynx contains 3 approximately orthogonal muscle groups, circumferential, longitudinal and radial, arranged in well defined layers. Pharyngeal peristalsis involves sequential circumferential constriction, apparently with coordinated local pharyngeal expansion produced by radial muscle. Circumferential and longitudinal muscles consist of discrete, well defined bands. The number, position and arrangement of circumferential and longitudinal bands show little interanimal variability; these bands are individually identified by sequential number. Regional morphologic specializations of circumferential bands presumably facilitate peristalsis. Circumferential and longitudinal bands form a two dimensional reference system defining position on the pharyngeal surface. In the accompanying paper circumferential motor fields are described in terms of identified motoneurons innervating identified bands, and radial motor fields are located with respect to the coordinate system of overlying longitudinal and circumferential bands.