Innervation of the crayfish thoracic deep flexor musculature

✍ Scribed by Crabtree, Robert L. ;Sherman, R. G.

• Publisher: John Wiley and Sons
• Year: 1980
• Tongue: English
• Weight: 825 KB
• Volume: 213
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402130104

✦ Synopsis

Abstract

The innervation and neuromuscular physiology of the deep flexor muscles in the thorax of the crayfish, Orconectes rusticus are described. Four muscles arise ventrally from the endophragmal shelf and join at segmental inscriptions to form a single functional mass. Deep flexor 1 (DF~1~) extends from the anterior thoracic endoskeleton to be joined by DF~2~, DF~3~, and DF~4~ in more posterior segments. The mass inserts on the abdominal flexor at the common flexor inscription.

Motor axons from thoracic ganglionic third roots 1–3 innervate the deep flexor muscles. Light and electron microscopical examination indicates that the third root of the first thoracic ganglion contains only three or four axons that innervate the musculature, and the third root of the second thoracic ganglion usually contains five. The largest number of deep flexor axons (10) occurs in the third root of the third thoracic ganglion.

Methylene blue staining and microelectrode recording methods show that each deep flexor muscle fiber is innervated by three motoneurons: the motor giant, a non‐giant excitor and an inhibitor. The motor giant elicits excitatory postsynaptic potentials (EPSPs) that rapidly antifacilitate, while the non‐giant excitor elicits EPSPs that do not antifacilitate. Both excitors produce spiking activity in the deep flexors. The inhibitory motor neuron reduces the amplitude and duration of the EPSP and prevents spiking activity. These results show that the thoracic deep flexor system is similar to the homologous system in the abdomen.