Each featured original illustration from the early 1900s, is accompanied by a caption written to engage scientists, researchers and investigators who populate the NIH campus.  As well as a 3-D printed rendering that enlarges a detail of the illustration above.  In this way, the drawings are rendered more accessible to a variety of audiences—including vision-impaired visitors who can directly experience these tactile versions of Cajal's drawings.  These  These files are made available on the 3D Print Exchange.  Direct links to the 3-D print files are provided at the end of this page.

The Cajal illustrations currently on-view include: 

• Auditory Tracts
• Axonal Tracts in Rat
• Cajal-Astrocytes
• Cajal Astrocytes
• Cerebral Cortex-ii
• Interneuronal Plexuses
• Medulla
  
  

Using the silver nitrate staining method to visualize these cells, he recognized that although the axons of the stellate neurons made numerous synapses with the Purkinje neuron cell bodies, they did not fuse at any point.  This supported his Neuron Doctrine, wherein the nervous system is composed of distinct cells rather than a network of continuously connected cells, and nervous impulses travel from the axon of one cell to the body of another.  

Although he first posited the Neuron Doctrine in 1894, it was not until the 1950s, when the first electron microscopes became available, that scientists were able to confirm the existence of the synapse and thus validate Cajal’s theory.Courtesy of the Cajal Institute, Spanish National Research Council or CSIC©

Astrocytes are a type of macroglia that are critical for maintaining physiological homeostasis in the CNS and supporting neuronal function.  Astrocytes in the grey and white matter of the brain typically have pedicles, or “feet”, that form contacts with capillaries (A, B, e) and control local blood flow.  

Using a uranium-nitrate technique specifically for staining astrocytes on a tissue sample bordering a cerebral wound, Cajal observed not only normal astrocytes in contact with capillaries, but also small amoeboid cells (a,b,c).  Other scientists, such as Alzheimer, had previously noted such cells in the CNS tissue of persons with various degenerative diseases, but their origins were uncertain.  Cajal correctly inferred that these cells were astrocytes which had somehow reshaped themselves after the injury.  

We now know that astrocytes become “reactive” after a brain injury: they become polarized, migrate, and their cell bodies swell.  Such reactive astrocytes are postulated to have both beneficial (wound healing, limitation of inflammation) and detrimental (scar formation) roles in the response to injury.Courtesy of the Cajal Institute, Spanish National Research Council or CSIC©

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The gross anatomy and function of the visual system had been a subject of human curiosity for nearly 2000 years by the time Cajal made his careful studies of its constituent neurons in the early 1900s.  His meticulous eye allowed him to recognize and distinguish most of the neuronal cell types we recognize today, although he had only the morphology of the stained cells to guide him.  

He arranged his descriptions of the primary visual cortex, the first processing center for visual signals within the brain, according to 9 layers clearly delineated by the types of cells present.  A subset of these layers are shown above: medium pyramidal cells (B, D, F) in layer 6 give rise to recurrent axons (a) which reach back to the outermost layer of the cortex, while the giant pyramidal cells (A, E) in layer 7 form horizontal dendrite bundles as well as axons that descend into the lower layers of the cortex.  

Cajal was the first to realize how short the horizontal axonal/dendritic connections between the cells of the primary visual cortex were, and to hypothesize the significance of this fact: information flows vertically through the layers of the cortex with little lateral spread.Courtesy of the Cajal Institute, Spanish National Research Council or CSIC©

While neurogliaform cells do form some classical synapsesclassical synapses, of the type that Cajal predicted, it is now known now known that many of their boutons do not have a specific a specific post-synaptic target; instead, they are able to able to mediate mass-signal transmission to nearly any neuronal any neuronal process within their axonal plexus using gammausing gamma-Aminobutyric acid.  Most modern research on research on neurogliaform cells has been performed on the hippocampusthe hippocampus, where they are hypothesized to provide to provide signaling cues to adult-born neurons.

Courtesy of the Cajal Institute, Spanish National Research Council or CSIC©