The B cell

In addition to the two acoustic receptor cells, A1 and A2, tympanic organ of noctuid moth includes a third neuron usually referred to as the B neuron or the B cell. It is a large neuron which enters the CNS via the tympanic nerve along with A1 and A2 axons. Within central ganglia its projections are very similar to those of the A1 neuron (Treat, Roeder, 1959; Surlykkå, Miller, 1982)

This cell is known to be the source of continuous and apparently spontaneous impulses in the tympanic nerve.

Central branchings of the three neurons from a moth ear

(from Surlykkå, Miller, 1982).

While the auditory receptor (A1 and A2) responses were extensively investigated, almost nothing was known about the function of the B cell. No direct interaction with the acoustic elements has been demonstrated (Treat, Roeder, 1959), and the function of the cell for a long time remained unknown.

The shape of B cell branching suggests that it has some close connection with the auditory system. In the course of studies of echolocation we suggested that it could serve as a detector of moth's own click, marking it out among different sounds.

To test the hypothesis one had to force a moth somehow to emit a click during the electrophysiological recording from the B cell. There was no way to do that in noctuids since their mechanism for click production induces the heavy vibration which goes through the whole body of a moth and that makes the reliable recording almost impossible. Fortunately there is a different moth family, Arctiidae, which are closely-related to Noctuidae. In this family the mechanism for sound production is different - particularly, of a tymbal type (Blest et al., 1963). Gently pushing the surface of the tymbal it is possible to generate a click so we were able to conduct the experiment recording from the B cell in Arctia caja (Arctiidae). Artificially evoked tymbal clicks of arctiids caused 2-3 spikes of the B cell with a latency of 3-6 ms (Lapshin, Fyodorova, 2000).

Examples of response to the artificially evoked tymbal click

The recordings were made from tympanic nerve of Arctia caja The moment of click generation is pointed by arrow.

Spikes belonging to the three axons within the tympanic nerve are easily discriminated by their amplitude.

What was also interesting, the responses of the most sensitive acoustic receptor cell (A1) on such stimuli was reduced in comparison with it's reactions to external sounds.

We have also described the B cell response to mechanical pushing of some points of thorax in noctuid moth Blepharita satura (Noctuidae). It demonstrated the increase of average spiking frequency.

After-stimulus histograms of tympanic receptor responses to mechanical stimulation of different areas of body.

Recorded from tympanic nerve of Blepharita satura Responses of three different neurons were discriminated by their amplitude (see the picture above). Each histogram is plotted from the results of 10 stimulus presentations.

A, B: responses of the B-cell to a puch applied to the upper part of metepisternum and to the base of the hindwing, accordingly;

C: changes in spontaneous activity of the acoustic receptor A1 in response to a push applied to the coxa.

The stimulus is shown below as the diagram of pressure change.


Treat A.E., Roeder K.D. (1959) A nervous element of unknown function in the tympanic organs of moths // J. Insect. Physiol. V.3. ¹2. P.262-270.

Surlykke A., Miller L.A. (1982) Central branchings of three sensory axons from a moth ear (Agrotis segetum, Noctuidae) // J. Insect. Physiol. V.28. N°4. P.357-364.

Blest A.D., Collett T.S., Pye J.D. (1963) The generation of ultrasonic signals by a new world arctiid moths // Proc. R. Soc. London, Ser.B V.158. P.196-207.

Lapshin D.N. Fyodorova M.V. The functions of the B-cell in the tympanic organs of nocturnal moths (Lepidoptera, Noctuoidea) // Sensornye Systemy. 2000. V.14. ¹5. P.148-155. (in Russian).