Musculotopic innervation of the primary flight muscles, the pectoralis (pars thoracicus) and supracoracoideus, of the pigeon (Columba livia): A WGA‐HRP study

Abstract

The distribution of motoneurons innervating the primary depressor and elevator muscles of the wing of the domestic pigeon (Columba livia) was studied by using the retrograde axonal tracer lectin-conjugated horseradish peroxidase (WGA-HRP). Injection of WGA-HRP into the pectoralis (pars thoracicus) labeled neurons in the ventromedial corner of the lateral motor column of the spinal cord. These neurons were arranged in a column extending from spinal segment X or XI to spinal segment XII or XIII. The pectoralis, the primary depressor muscle of the wing, consists of two parts which are anatomically and functionally distinct, the sternobrachialis (SB) and thoracobrachialis (TB). Injection into the SB labeled neurons in the rostral and middle regions of the pectoralis motoneuron column. In contrast, injection into the TB labeled neurons in the middle and caudal regions of the pectoralis motoneuron column. Injection into the primary elevator muscle of the wing, the supracoracoideus, labeled neurons in the lateral motor column in spinal segments X and XI. These motoneurons were located dorsolateral to motoneurons labeled following pectoralis injection. These data demonstrate musculotopic segregation of the motoneurons innervating the primary flight muscles in the pigeon and, further, illustrate that the SB and TB subregions of the pectoralis are innervated by discrete aggregations of motoneurons.

Neuromuscular control of wingbeat kinematics in Anna's hummingbirds (Calypte anna)

“…This, despite the fact that the hummingbird pectoralis major is innervated by a large motor pool spanning several spinal segments, as are the pectoral muscles of other birds (E. R. Donovan, B. K. Kenney and D.L.A., unpublished observations) (Sokoloff et al, 1989). Hummingbirds are therefore synchronizing hundreds of motoneurons during the behaviors reported here.…”

Widespread accumulation of [ 3 H]testosterone in the spinal cord of a wild bird with an elaborate courtship display

“…Therefore, we assume that at least some of these sex steroid-accumulating motoneurons in manakins are also part of androgendependent neuromuscular systems. Because in manakins the majority of sex steroid-accumulating cells are found in the cervical and lumbosacral enlargements, and motoneurons in these enlargements largely control muscles of the upper and lower extremities (19,29), these cells may be involved in multiple behavioral functions, perhaps innervating muscles controlling the elaborate dancing and wing-snapping of these birds.…”

“…Cellular position in the rostrocaudal plane was established by observing landmarks such as visible dorsal-root ganglion, the beginning of the cervical enlargement that starts at C10 in the pigeon (19), and the lumbosacral enlargement that starts at L1 in the pigeon (20). Cells in the dorsoventral axis were located by estimating the proximity of the cell to Lamina IX (20), a morphologically prominent motoneuronal cell column throughout the ventral horn.…”

Neuromuscular Correlates to the Evolution of Flapping Flight in Birds

“…A functional subset of motoneurons (= motoneuronal pool) within the motornuclei of these muscles has not been identified. At least two motoneuronal pools have been identified within the pectoralis motor nucleus of pigeons [Sokoloff et al, 1989[Sokoloff et al, , 1998] which might also be the situation for the European starling. The consistent rostro-caudal and dorsolateral offset of the SB and TB motoneuronal pools support this hypothesis.…”