Biology Reference
In-Depth Information
towards the orea serrata. Thus, he could provide explanation both
for Schultze's paradox of the observed acuity difference between the
rod and cone systems, and the decrease in acuity performance with
eccentricity.
The structural arrangement and synaptic connections of the
primate retina shown by Polyak by the Golgi method also provided
new insight into the light sensitivity difference between the rod and
cone systems. Since many more rods than cones were connected
to a given functional unit, more rod impulses could be combined
and, thereby, make the rod system the most sensitive. Hence,
photochemical differences between the cone and rod receptor type
could no longer be regarded as the sole explanatory factor of the
greater rod sensitivity.
6.7 The functional potentials of the
synaptic arrangement
Even more important, the histological investigation of the retina
with the Golgi method revealed that the retinal neural tissue was not
composed of intimately related neurons in continuous nerve nets or
nerve webs, but was made up of individual nerve cells only in contact
with each other through synapses. This profound insight into the
structure of the neural system had been revealed by Cajal in the late
1880s (see Cajal, 1937 ), but it was not until Polyak (1941) published
his great work that the full functional potential of the primate retina
became apparent. Thus, Polyak revealed that the neural structure
of the primate retina was much more complicated than previously
held. Both the bipolar and ganglion cells were composed of several
varieties woven into an intricate synaptic pattern. Such a structure,
of course, made possible much more varied reactions than a neuron
network or neuron web composed of neurons of the same or similar
kinds. In particular, Polyak pointed to the possibility that the location
and number of synaptic contacts might affect both the kind and
magnitude of an input received by a neuron, and that horizontal and
amacrine cells might be involved in facilitation and inhibition of the
 
Search WWH ::




Custom Search