Images & Figures

Figures

Neuromodulatory Pathways in the Stomatogastric Nervous System

Neuromodulation can occur through direct or indirect pathways. My focus is on the labral sensory neurons which indirectly modulate the gastric mill rhythm through the decending neurons within the commisural ganglion (CoGs)

Interruption of the Gastric Mill Rhythm by the Labral Nerve

Electrical stimulation of the labral nerve interrupts the gastric mill rhythm (n=5). This appears to occur via inhibition of descending modulatory neurons (n=5).

Number of Cell Bodies Observed in Each Location

The number of cells observed in each population varied between individuals for 2 out of the 5 locations: right lateral and left lateral. The right and left turn locations were only ever observed with one cell present.

Dissection Methods

In order to trace the labral nerves, I dissected out the labrum and pinned it out as flat as possible. I then dyed it with Methylene Blue vital dye to label the axons and cell bodies. The green arrows in the figure indicate the labral nerves in each stage of dissection.

Sensory Neurons Found in the Crustacean Labrum

5 locations of neural cell bodies have been observed in the crustacean labrum extending from branches of the labral nerve. The left and right "turn" cells have only ever been one cell body, while the left and right "lateral" populations have typically been more than one cell body. The two populations are named the "turn" cells because they are at the location where a branch of the labral nerve wraps around a muscle and dives posteriorly into the pouch. Farther posterior than this is where the right descending population was seen. This cell body population has only been observed in one individual.

Swallowing Response Initiated from Physical Touch and Saline Application

Resting Labrum

This is how the labrum sits above the esophagus in absence of stimulus in the live crab and in dead crabs. The arrow indicates where touch with forceps was applied to elicit the swallowing behavior.

Opened

After touching the labrum with forceps in the area indicated in the previous figure, the labrum retracts to uncover the esophagus and the esophagus opens. This also occurs when saline is applied to the labrum and mouth area.

Closed

Following the opening in the previous figure, the labrum moves past its resting position and further over the esophagus to cover the opening and the esophagus closes as well. This cycle repeats a few times following 1 stimulus application.

Video of swallowing response of the labrum after a touch stimulus.

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