ABSTRACT
Single shocks to the column sometimes evoke tentacle contractions, ranging from slight movement of a few scattered tentacles to rapid bending or shortening of all the tentacles. Some individuals are more responsive than others. Complex bursts of electrical activity follow single shocks, but only in tentacles that contract.
These single shocks excite pulses in two conducting systems - the through-conducting nerve net (TCNN) and the ectodermal slow conduction system (SS1). When a single shock evokes contractions and bursts of electrical activity, these usually follow the SSI pulse, rarely the TCNN pulse. Stimulation of the SS1 alone causes tentacle contraction in responsive anemones.
Fast tentacle contractions always follow the second of two closely-spaced TCNN pulses: the TCNN shows facilitation (Pantin, 1935a). An SSI pulse, however, does not facilitate subsequent pulses in either the SSI or TCNN.
There are two pathways for activation of tentacle contractions. The TCNN pathway is mechano-sensitive and normally requires facilitation. The SS1 pathway is mechano- and chemosensitive, only requires a single SSI pulse to evoke contraction, but is very labile. It is proposed that the TCNN and the SS1 do not excite the ectodermal muscles directly, but via a multipolar nerve net.
