The responses of the antennular muscles of the brachyuranScylla serrata (Forskål) (Portunoidea, Brachyura) to repetitive activation of specific motoneurons
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The electrical and mechanical responses in all the antennular muscles of the medial and distal segments of the antennule ofScylla serrata, in response to repetitive stimulation of all the antennular motoneurons at 10, 20, 50 and sometimes 100 Hz, are described.
In muscle group 30 both M30V and M30D contract and relax relatively slowly. The EJPs of motoneurons to this muscle group always show some facilitation. Tension production always occurs smoothly and is accompanied by a plateau of depolarisation in the muscle fibres.
In muscle group 31 both M31Sv and M31Sm contract and relax slowly whereas M31F contracts and relaxes rapidly. Motoneuron A31S1 gives rise to facilitatory EJPs in both ‘slow’ muscles whereas the large EJPs of A31S2 do not show facilitation. Motoneuron A31F gives rise to large, facilitatory EJPs in M31F whereas motoneuron A31–32F gives rise to very large EJPs in M31F which show some antifacilitation even at 20 Hz.
In muscle group 32, M32F contracts and relaxes very rapidly whereas M32S contracts and relaxes slowly. Even at 50 Hz the EJPs of motoneurons A32F and A31–32F do not show any facilitation or antifacilitation. The EJPs of motoneuron A32S1 are relatively large and do not show any facilitation. Each of these EJPs elicits a small, slow contraction in M32S and summation of these results in the production of a plateau of tension even at 10 and 20 Hz. The EJPs of motoneuron A32S2 facilitate only slighly and evidence suggests that the plateau of tension produced arises, in part at least, from the summation of small slow contractions produced by each EJP.
Motoneuron A32F-S gives rise to facilitating EJPs in M32F but non-facilitating EJPs in M32S. Paradoxically this motoneuron does not produce any tension in M32S but at 100 Hz does produce large, possibly electrogenic, responses in M32F which are accompanied by twitch contractions.
The behavioural role of particular antennular motoneurons is discussed and compared with previously published data on the hermit crab antennule.
KeywordsMuscle Fibre Mechanical Response Muscle Group Distal Segment Hermit Crab
excitatory junction potential
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