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2.1). |
2.2A). |
2.2B). |
3.3). |
I. |
Adapted from Cajal |
(1909–1911). |
AB C |
e |
e |
e |
e |
e |
e |
e |
s s |
mm |
stimulus |
FIGURE 2.3 Activation of effector cells (e) in simple animals. |
(B) In cniderians, bipolar sensory neurons (s) differentiate in the ectoderm. |
The sensory neuron outer |
process detects stimuli and is thus a dendrite. |
Arrows show the direction of information fl ow. |
2.3). |
BASIC PLAN OF THE NERVOUS SYSTEM |
I. |
2.2B, 2.3C). |
In this hypothetical scenario (Fig. |
Then the axon of each moto- |
neuron innervates an effector cell population. |
One is a typical axon innervating an |
effector cell population. |
However, the other is a process |
that contacts homologous processes from other moto- |
neurons. |
Con- |
sider a stimulus to one specifi c part of the animal or |
even one sensory neuron. |
2.1). |
2.4). |
2.5). |
The |
largest, most complex ganglia (cephalic ganglia) are |
I. |
2.6). |
They are typical neurons conforming to the |
functional polarity rule. |
There are, however, three other critical functions |
interneurons subserve. |
Refer to McConnell (1932) and |
Koizumi (2002). |
Refer to Lentz (1968). |
Reproduced with |
permission from Yale University Press. |
Sensory neurons (s) usually innervate |
motoneurons and interneurons but not effectors (e). |
Arrows show |
the usual direction of information fl ow. |
EVOLUTION HIGHLIGHTS: GENERAL ORGANIZING PRINCIPLES 19 |
20 2. |
BASIC PLAN OF THE NERVOUS SYSTEM |
I. |
NEUROSCIENCE |
By this defi nition the vast majority of vertebrate |
brain neurons are interneurons. |
However, he eventually entered the Univer- |
sity of Zaragoza and received a medical degree in 1873. |
2.2A). |
This concept became known as the neuron |
doctrine. |
The meeting in Stockholm may not have |
diminished the great personal friction between them. |
2.6). |
Features of simple nervous systems are preserved |
throughout evolution. |
2.7). |
2.8, 2.9). |
2.9). |
Note nerves extending |
from ventral nerve cord and cerebral ganglia. |
Refer to Brusca and |
Brusca (1990). |
EVOLUTION HIGHLIGHTS: GENERAL ORGANIZING PRINCIPLES 21 |
22 2. |
BASIC PLAN OF THE NERVOUS SYSTEM |
I. |
NEUROSCIENCE |
motor information. |
Here we simply consider macroscopic |
structural changes during the transformation. |
2.10). |
2.8) as well as the |
length of the embryonic neural plate and neural tube (see |
Figs. |
2.10 and 2.12). |
2.8. |
The basic principles are much easier |
to illustrate than to describe in writing (see Fig. |
The other source of confusion is simply the dif- |
ferent names that are used. |