The Giant Axon Escape System of A Hydrozoan Medusa, Aglantha Digitale

• DOI: 10.1242/jeb.84.1.303
• Publication Date: 2021-04-25T15:16:26Z
• Authors: Alan Roberts; G. O. Mackie
• Keywords: Tentacle (botany); Axon hillock

ABSTRACT Aglantha digitale (Hydrozoa) has a ring giant axon, up to 35 μm in diameter, which runs all round the margin of bell outer nerve-ring. Running from margin, inside towards apex are eight motor axons, 40 diameter. These synapse with sub-umbrellar myoepithelium and therefore motoneurones. The myoepithelial cells line have striated muscular tails running circumferentially. Contraction this circular musculature forces water out propels medusa through water. A large axon (up 7 diameter) on aboral side each tentacle. tentacles retract during swimming contain longitudinally aligned muscle tails. Intra- extracellular recordings axons indicate that they involved rapid escape response Aglantha. Stimuli evoke lead brief burst two six impulses (2–3 ms duration) axon. propagate (at 2·6 m s−1). tentacle fire one-to-one contract. excited at chemical synapses (blocked by divalent cations synaptic delay 1·6 ± 1 ms), where large, facilitating epsps an impulse then propagates 4 s−1. overshooting Na+ dependent, 2–3 duration, excite delay. regenerative is evoked. It long duration (15–70 Ca2+ overshoots zero, 0·22 0·29 ms−1. nearly synchronous contraction whole subumbrellar Isolated strips can reach peak tension ms. In absence sarcoplasmic reticulum, for excitationcontraction coupling probably enters impulse. This preparation allowed clear understanding how types co-ordinate behaviour. should also be valuable study transmission, previously very inaccessible Cnidarians.