Descending Pathways to the Spinal Cord in Tetrapods: A Brief Outline

Available experimental data on the cells of origin, funicular trajectory and site of termination of descending supraspinal pathways in amphibians (ten Donkelaar et al. 1981; ten Donkelaar 1982; Tóth et al. 1985; Naujoks-Manteuffel and Manteuffel 1988), reptiles (ten Donkelaar et al. 1980; ten Donkelaar 1982), birds (Cabot et al. 1982; Gross and Oppenheim 1985; Webster and Steeves 1988; Webster et al. 1990) and mammals (see Kuypers 1981 for review; for data in opossums see Martin et al. 1975; Crutcher et al. 1978; Holst et al. 1991) show that throughout tetrapods a basic pattern in the organization of descending pathways is present. The most notable difference between nonmammalian tetrapods and mammals is the apparent absence of somatomotor cortical areas giving rise to long descending projections to the spinal cord.