Localization of the Motoneurons Innervating the Hindlimb Muscles in the Spinal Cord of the Domestic Fowl

Abstract

The origins of the motor nerve fibers supplying the individual hindlimb muscles were elucidated in the fowl by the retrograde degeneration method. Chromatolytic cells were seen in the ipsilateral lamina 9 of the lumbosacral enlargement. Motoneurons innervating the individual hindlimb muscles were localized in the characteristic position of lamina 9. Both hip and thigh muscles are supplied by motoneurons of almost all the columns in lumbar segments and by those of dorsolateral columns in sacral segments, while the shank and foot muscles are supplied by motoneurons of ventromedial columns in sacral segments. The origins of the dorsal cord of the lumbosacral plexus are situated laterally in the lamina 9 and those of the ventral cord are located medially in it. U.S. 142 OHMORI, WATANABE and FUJIOKA 3 -0minutes. The lumbosacral enlargement of the spinal cord was removed, immersed in the same fresh fivative for more than a week, and then embedded in paraffin in the conventional manner. Transverse sections 15pm thick were cut serially and stained with lux01 fast blue and cresyl fast violet (KL~VER/BARRERA, 1953). Chromatolytic cells with a distinct nucleolus were counted.In addition to these fowls, some birds were used for identification of hindlimb muscles and nerve supply. Results I. NomenclatureNomenclature of hindlimb muscles and nerves supplying them is essentially in accordance with the Nomina Anatomica Avium (VANDEN BERGE, 1979; BREAZILE/ YASUDA, 1979). The spinal cord which has a segmental structure sends out 41-42 pairs of spinal nerves in the fowl. An arbitrary line is drawn in the middle level between the most caudal rootlet of a ventral root and the most cranial rootlet of the next, and serves as the demarcation with the neighboring segments. The region between the two lines is regarded as a "spinal segment" for each spinal nerve.

Topographic Position of Forelimb Motoneuron Pools Is Conserved in Vertebrate Evolution

“…The present investigation of reptilian and mammalian forelimb motor pools is consistent with previous studies of the motor pools in birds [Ohmori et al, 1982;Straznicky and Tay, 1983] and those in other terrestrial mammals [Horner and Kummel, 1993]. The position of forelimb motor pools in the transverse and frontal planes, with respect to the brachial plexus, shows little variation either within species or between vertebrate classes.…”

“…Using these techniques, we mapped the position in the spinal cord of each motoneuron pool for seven forelimb muscles in a representative mammal (Mus musculus) and reptile (Iguana iguana). These motor pool maps are consistent with maps of homologous muscles in an avian wing [Ohmori et al, 1982;Straznicky and Tay, 1983] and provide additional evidence that motoneuron pools remain largely conserved across vertebrate classes.…”

“…5). Although the pools remain distinct, domestic fowl exhibit a greater degree of motor pool overlap along the rostrocaudal axis [Ohmori et al, 1982]. For example, the avian pectoralis pool extends from spinal nerves 14 to 16, overlapping the posterior half of the supracoracoideus and biceps pools.…”

“…Error bars denote standard errors. dal to the supracoracoideus, spinodeltoid, and biceps pools and, thus, the general topography is maintained with iguanas and mice [Ohmori et al, 1982;Straznicky and Tay, 1983].…”

“…Cervical spinal nerves 5 to 8 and the first thoracic nerve (nerve 9) contribute to the brachial plexus in mammals. The position of the brachial plexus in birds varies with the length of the neck, but in domestic fowl it consists of spinal nerves 13 to 17 [Ohmori et al, 1982]. Individual motor pools within a species have a constant location with respect to adjacent motor pools and the margin of the ventral horn.…”