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Innervation of the Anterior and Posterior Levator Muscles of the Fifth Leg of the Crab Carcinus Maenas
1 Department of Zoology, Washington State University, Pullman, Washington, 99164, USA
In the fifth pair of legs, the anterior levator muscle of the basi-ischiopodite (AL) consists of a dorsal thoracic head (ALd), two closely aligned ventral thoracic heads (ALv) and a small coxal head (ALc). Major thoracic subdivisions are separately innervated, whereas the nerve innervating the coxal head projects from ALd. The posterior levator (PL) is located in the coxa and is separately innervated.
Nerve recordings, dye backfilling, muscle fibre recordings and nerve crosssections yielded somewhat different estimates for the levator motor innervation.
Nerve backfills reveal at least 10 motoneurones supplying AL: six shared by ALd and ALv, one unique to ALv and three unique to ALd.
Nerve recordings reveal six motoneurones supplying ALd and five supplying ALv. Four (including the common inhibitor) are shared by ALd and ALv and six project from ALd to ALc.
Most AL muscle fibres are innervated by two or three motoneurones, but fibres innervated by five were encountered. Postsynaptic potentials ranging from small (<1-5 mV) to large (15-25 mV) were found distributed throughout AL.
PL is innervated by two excitors not shared with AL and by the common inhibitor.
Electron micrographs reveal more axons than any of the methods for counting motoneurones. Neurones with axon diameters below 3 µm are likely to be sensory.
Key words: basi-ischiopodite, inhibitory/excitatory motoneurones, light/electron micrographs, nerve recordings, dye mapping, brachyuran arthropod
Accepted on September 18, 1986
