In the examples we’ve just mentioned, looking for food, looking for a mate, pupil constriction, and preventing falls are behaviors that are very closely related to survival and reproduction.
By adapting this response, an organism can ensure that, for most of its life, it will be able to cope with the dangers and temptations that are common in the environment, find a mate and carry on the family line.
Stimulation – the realization of the reflex: only two cells are needed.
Talking about the importance of the stimulus-reflex pattern, do you know how this pattern works in the brain of an animal?I want to use a very classic example to talk about this.
The main character in this example is an animal called the sea hare.
Note that this animal is not a rabbit, but is actually a mollusk that lives on the bottom of shallow seas.The body is about 10 centimeters long and looks a bit like an elephant clam with its shell removed.
It is so called because it has a pair of long, soft antennae on its head, which are a bit like the long ears of a rabbit.
The sea hare is a very important object in the study of neurobiology.An important reason is that in its body, the pattern of stimulus reflex is very easy to study and understand.
Specifically, like other mollusks, sea hares breathe through their gills.The sea hare’s gills are located inside its body and connected to the sea water by a hose.
How does the water get into the gills?The pipes are covered with tiny hairs that wiggle to drive seawater into them, allowing the gills to get oxygen from the flowing water.
It is conceivable that the sea hare’s gills are crucial to its survival.Therefore, protecting the gills is the most important thing for the sea hare.
So the sea hare developed a pattern of improvisational responses called the shriveled gills reflex.
If the sea water suddenly and violently hits the sea hare, or if a natural enemy violently hits the sea hare, it will quickly and tightly wrap its gills to prevent it from being hurt in the violent deformation of its body.
This shrivelled reflex is so important that it requires only a very simple and stubborn biology, namely the stimulus-reflex pattern.
And it’s as simple as two nerve cells.
First, there’s a sensory nerve cell attached to a sea hare’s water pipe.
If there’s a big bang from the sea, the nerve cell senses it and converts the environmental stimulus into a bioelectrical signal.
The second is a motor nerve cell attached to the gills that controls the contraction of the muscles around the gills.
There is a direct connection between this sensory nerve cell and the motor nerve cell.The output of the former, the axon, and the receiving end of the latter, the dendrites, can transmit electrical signals directly.
In this way, the sea hare’s shriveled gill reflex is understood very simply.