Seeing the Nervous System, Advanced Brain Imaging techniques, and more
Updated: Dec 11, 2018
Can we see the nervous system with the naked eye? Well, the retina of the eye is indeed an outgrowth of the developing brain (from the ectodermal tissue within the developing embryo), and thus considered a part of the central nervous system. Is it possible to physically view the retina? Based upon the figure below, the retina is present at the back of the eye, and thus cannot be viewed simply by looking at a mirror. However, there are methods to view one’s retina indirectly; Else, the alternative option would involve physical surgery upon the retina in order to locate it.
Figure 1. The Retina
Moreover, viewing the nervous system depends primarily on the definition of the above term. If you refer to individual neurons themselves, they would be impossible to see unless cultured in a laboratory and viewed under a microscope. However, if you are referring to entire nervous systems, then yes, it is definitely possible to view the central nervous system.
This is because the central nervous system comprises of the brain and spinal cord (and retina), which are often exposed during neurosurgery or, possibly, orthopedic surgery for spinal cords. These involve a significant amount of drilling, anesthesia, and careful peeling away of the protective dura, arachnoid and pia maters, and are therefore not necessarily the most accessible methods to view the nervous system - however, it is indeed possible.
Figure 2. Protective layers of the brain
A less ethically challenging (although still incredibly demanding) method would be to obtain mouse or animal models and perform a similar surgery on them; However, similar to human models, animals must be earned for testing and thus can usually only be obtained at post-doctoral levels.
Alternatively, there have been initiatives to make the brain ‘transparent’ in order to provide a clear picture of neuronal connections. This involves the addition of the SDS detergent that degrades lipids (fats) in the brain that occlude light, resulting in a see-through brain. Although not quite matching your request of a naked eye, this comes very close and allows for a much more detailed analysis into the synapses formed between neurons within the brain. This could lead to some interesting 3-Dimensional images into sliced brain tissue:
Figure 3. A 3-D image of a clarified brain image from below .
Lastly, I wanted to highlight the significance of brain-imaging in elucidating its neural networks. I recently read an article discussing the development of new, incredibly powerful MRI scanning machines with minimal, harmless temporary side-effects. This involves the utilisation of an extremely strong magnetic field (up to 10 Tesla), as compared to the standard 1.5–3T magnets. The result? An image similar to the one below, which was only generated using a 7T magnet:
Although it does not yield exact information of the neurons in the brain, MRI scans can provide insight into the structural organization of the brain and thus further information about its neuronal structures. Do read the linked article if interested!
With regards to the peripheral nervous system, to my knowledge it is not possible to be seen directly with the naked eye - simply due to the extensive amounts of collagen (skin tissue), muscle and bone contained within our bodies that burrow the actual neural connections to them, as opposed to the bunched-up concentrated location of neurons in the brain.