Repetitive Vocalizations Evoked by Local Electrical Stimulation of Avian Brains; pp. 393–407

Abstract

Factors affecting the tension on the external tympaniform membranes of the syrinx during respiration and vocalization were studied in 35 adult chickens. These membranes are controlled by the interaction of the sternotrachealis and the tracheolateralis muscles, tracheal air flow, and interclavicular air sac pressures to produce sound. The muscles are innervated by the hypoglossal nerves, with the left nerve playing the dominant role in innervating both the left and the right sternotrachealis muscles. Contraction of the tracheolateralis muscles applies tension on the external tympaniform membranes, holding them out of the tracheal air flow. The sternotrachealis muscles relax the membranes by pulling the trachea caudally. This allows interclavicular air sac pressure to push the membranes into the tracheal air flow which causes them to vibrate and produce sound. Section of the sternotrachealis muscles eliminates low level vocalizations and alters the character of calls at any intensity. Inactivating both pairs of muscles has less effect on vocalization because, without the tension caused by the tracheolateralis muscles the external tympaniform membranes are already relaxed, eliminating the need for the sternotrachealis muscles. Loss of pressure in the interclavicular air sac will stop vocalizations in chickens, even when the tracheal air flow is maintained at a rate adequate for calling. Tracheal air flow and interclavicular air sac pressure changes both result from the direct action of the respiratory muscles.

The songbird syrinx morphome: a three-dimensional, high-resolution, interactive morphological map of the zebra finch vocal organ

“…The ST has also been hypothesized to function as an adductor of the syringeal labia [99] and as an antagonist to the TL in many non-songbirds [95,102-108]. The ST muscle is present in all songbirds, and is missing only in very few bird species that are either non-vocal or that produce song with little frequency modulation (for example, the new world vultures [109,110] or Darwin's nothura ( Nothura darwinii [111]).…”

Innervation of the syrinx of the zebra finch (Taeniopygia guttata)

“…However, only XIIts motoneurons were labeled when wheat germ agglutinin was injected into the ventral syringeal muscles (Bottjer & Arnold, 1982;Wild, 1981), supporting the idea that the ventrolateral nucleus projects to extrinsic tracheosyringeal muscles (Wild, 1981). Cells in a similar ventrolateral position have been traced in the fowl from injections into the ypsilotrachealis or cleidotrachealis muscle (Youngren & Philips, 1983), a muscle that originates on the clavicle, inserts into the upper trachea (George & Berger, 1966), and is active during phonation (Youngren, Peek, & Phillips, 1974). In passerines, this muscle also inserts in the rostral trachea, far from the syrinx (Shufeldt, 1890 in the raven; personal observations in the zebra finch), but a role in vocalization seems unlikely because, unlike XIIts motoneurons, the motoneurons ventrolateral to XIIts that probably innervate this muscle do not receive a descending projection from the telencephalic song control system (Wild, 1993).…”

Bilateral innervation of syringeal muscles by the hypoglossal nucleus in the jungle crow (Corvus macrorhynchos)

“…Previous studies have shown that the syringeal muscles of non-oscines are controlled by the nXII bilaterally. For example, in the domestic fowl ( Gallus domesticus ), the left NXII descends toward the syrinx on the Musculus trachealis laterali , which is attached to the lateral side of the trachea, and provides a portion of the innervation of the contralateral muscles (Youngren et al 1974;Youngren & Phillips 1983). A cross-connection between the left and right nXII occurs in the mallard (Lockner & Youngren, 1976;Brackenbury, 1982).…”