What's the Point?

After looking at all these sections and slides and close-ups of the various types of brains, what have we learned? What kinds of trends have we observed? What are we still curious about?

When you saw the sagittal slices of all the brains, what did you notice? Comparing across the sections you probably noticed that there were some general differences between the brains (involving size, shapes of structures, etc). For example, it may seem easier to differentiate structures in the human brain as opposed to the rat brain. It has been found that as one ascends a phylogenetic sequence, there is clearer definition and demarcation of structures, almost as if the brain is better organized. Yet, the closer we got, especially when we made forebrain and hindbrain slices, the more you may have realized that the brains and their structures look quite similar. In other words, yes, there are differences between animals' brains but also deep and fundamental similarities. Here are some pictures to remind you:

Cross-section of cat hindbrain group of brains - midsagittal slice cross-section of monkey hindbrain
Cat Hindbrain Cat, Monkey, Human -- Midsagittal View Monkey Hindbrain

 Rat brain vs. Frog brain

As you can see above, both the cat and monkey cerebellums look rather similar. The structure is located in similar places on each respective brain, above the brainstem, and is rather convuluted. Yet, there are also general differences that make it easy to differentiate one from another.

Another interesting comparison is between the rat and frog brains. Look at the picture to the right and note any similarities and differences. This may be difficult for you to see due to the fuzziness of the photograph, but stick with me. The frog brain is on the bottom; the middle brain is a sagittal view of the rat brain; the top brain is a full view of a rat brain. Essentially, the frog brain resembles the basic structures of the rat brain, laid out flat. For example, you see the spinal cord leading to the brain stem and cerebellum and then the midbrain/forebrain structures. So, in this way, the rat and frog brains are quite similar. Yet, in the rat brain we find neocortex surrounding the mid- and forebrain, which we cannot see in a frog brain. Indeed, frogs do not have neocortex (remember -- only mammals have this multi-layered structure). Click here for a discussion about this.

 

Magnified neuron

What if we look even closer, at the cellular level? What if we magnify these pictures so that we can see individual neurons?

Click here to see individual neurons

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