Morris J L
Am J Physiol. 1976 Oct;231(4):1272-8. doi: 10.1152/ajplegacy.1976.231.4.1272.
The sphincter pupillae muscle cells in the iris of Bufo marinus contract autonomously in response to bright light, causing a rapid constriction of the pupil. A strong sympathetic beta-adrenergic inhibition of the sphincter pupillae is apparent in this species. The inhibitory fibers can originate in the second, third, or fourth ventral spinal roots. No strong, consistent excitatory innervation of the toad iris was detected, even by transmural stimulation of the isolated iris. Pupilloconstriction occasionally resulted from stimulation of the 3rd or 5th cranial nerves, but the effect was small (10-20% of the magnitude of the light response) and inconsistent. It therefore appears that the toad must regulate pupillary diameter by balancing myogenic contraction, in direct response to light, against neurogenic (sympathetic) relaxation of the sphincter pupillae.
海蟾蜍虹膜中的瞳孔括约肌细胞会因强光自主收缩，导致瞳孔迅速收缩。在该物种中，对瞳孔括约肌存在明显的交感β-肾上腺素能抑制作用。抑制性纤维可起源于第二、第三或第四腹侧脊髓神经根。即使通过对分离出的虹膜进行透壁刺激，也未检测到对蟾蜍虹膜有强烈、持续的兴奋性神经支配。刺激第三或第五对脑神经偶尔会导致瞳孔收缩，但效果较小（仅为光反应幅度的10 - 20%）且不恒定。因此，蟾蜍似乎必须通过平衡直接对光作出反应的肌源性收缩与瞳孔括约肌的神经源性（交感）舒张来调节瞳孔直径。
