NEURAL ACTIVIT"!' IN THE RETINA 



695 



FIG. 2. A. Scheme of the structures of the primate retina as revealed by the method of Golgi. 

 The layers and the zones are designated as follows: (/) pigment layer; (,2-a) outer zone and (^-A) 

 inner zone of the rod and cone layer; (5) outer limiting membrane; (_4-a) outer zone and (^-A) 

 inner zone of the outer nuclear layer; (is-a) outer zone, (j-A) middle zone and (j-c) inner zone 

 of the outer plexiform layer; (5) inner nuclear layer with its four zones; (7) inner plexiform layer; 

 C5) layer of the ganglion cells; (9) layer of the optic nerve fibers; and (/o) inner limiting membrane. 

 The nerve cells are designated as follows: (a) rods, (A) cones, (r) horizontal cells, (d, e, f, A) bi- 

 polar cells, (i, /) so-called 'amacrine cells', (m, n, 0, p, i) ganglion cells and 00 'radial fibers' of 

 Miiller. In this scheme the nervous elements are reduced to their essentials, with, however, the 

 characteristic features of each variety preserved — the location of the cell bodies, the size, the shape, 

 and the spreading of the dendrites and of the axis cylinders — and with the synaptic contacts pre- 

 sented accurately. [From Polyak (122}.] 



B. The structure of the primate retina reduced to its essentials, including the synopsis of the 

 propagation of the retinal impulses from the photoreceptors to other parts of the retina, to the 

 brain, and from the brain back to the retina (direction indicated by the arrows). The marking 

 of the layers and the zones the same as in A. Labeling of the cells: (a. A) rods and cones, the pho- 

 toreceptors where the nervous impulses are generated by physical 'light' (in the scheme only the 

 left group of the photoreceptors is assumed to be stimulated by light); (c) horizontal cells which 

 transmit the impulses to the surrounding rods and cones; (_d, c, /, A) centripetal bipolar cells of 

 the mop, brush, flat and midget varieties, which 'transmit' the impulses from the photoreceptors 

 to the ganglion cells, the bipolars serving as 'analyzers'; (i) centrifugal bipolar cell, a variety of 

 the 'amacrine cells,' which probably receives the impulses from the centripetal bipolars from the 

 ganglion cells, and also from the brain by way of the centrifugal or efferent fibers (/) and trans- 

 mits them back upon the photoreceptors (a. A); (/) an 'amacrine cell' which possibly intercepts 

 a part of the bipolar impulses and spreads them over the surrounding territory; and (m, n, 0, p, j) 

 ganglion cells which receive impulses from the centripetal bipolars and transmit them to the brain 

 along their axon called 'optic nerve fibers.' [From Polyak (122).] 



bodies. The brush and flat bipolars reseinble each 

 other and occur everywhere in the retina from the 

 fovea to the ora serrata. They have large dendritic 

 territories. Their most interesting properties seem to 

 be: a) a "reciprocal overlapping of each of the den- 

 dritic territories with its own kind" (122) and 6) 

 axodendritic articulations with the ganglion cells. 

 The midget system also intermingles with this wide 



a.xodendritic or plexiform (inner plexiform layer) 

 network. The basic pattern consists of bipolar ter- 

 minals, ganglion cell dendrites and the Golgi type II 

 of cells called amacrines. Similar large plexiform net- 

 works with Golgi type II of cells are found elsewhere 

 in the nervous system, including the cortex of the 

 cerebellum. 



The ganglion cells, for physiological correlations. 



