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Journal of Experimental Biology 58,767-784 (1973)
Published by Company of Biologists 1973

The Motor Innervation and Musculature of the Antennule of the Hermit Crab, Pagurus Alaskensis (Benedict)

P. J. SNOW ¹

¹ Zoology Department, University of Alberta, Edmonton, Alberta, Canada

1. The motor innervation and musculature of the medial and distal segments of the hermit-crab antennule have been described anatomically.

2. Intracellular recordings within these muscles and simultaneous monitoring of whole-muscle tension have been used to define the motoneurones and contractile properties of the muscle fibres they innervate.

3. The motor system consists of two fast, two slow and one mixed muscle which are innervated by seven motoneurones.

4. The motor innervation is such that this system may be divided into three components: phasic, phasic-tonic and tonic. The possible involvement of these components in the antennular activities is discussed.

5. The tonic component is adapted to produce fine tonic tension in response to relatively low-frequency (5-10/sec) motoneurone discharge. It is suggested that this may be important for the postural control of appendages which, owing to the density of the environmental medium, are relatively weightless.

6. No evidence of postsynaptic inhibition was found, and this is discussed in relation to the movements of the antennule.