Grey and white matter
Cut across, the brain shows two shades. The grey matter, the cortex on the surface and the nuclei deep inside, is where the bodies of the nerve cells sit and their connections are made. The white matter under the cortex is cabling: billions of nerve fibres wrapped in fatty myelin, which gives it its colour.
A human brain cut across from side to side: grey cortex over white matter, the two thalami (2), and below them the midbrain (3), pons (4), medulla (5) and spinal cord (6)Wikimedia Commons, John A. Beal, Louisiana State University Health Sciences Center Shreveport, CC BY 2.5 (Human brain frontal (coronal) section description.JPG)
The fibres run three ways. Some join areas within one hemisphere, some cross to the other hemisphere, and some run between the cortex and the brainstem and cord. These gather into a fan, the internal capsule, which passes between the deep nuclei. A small stroke there can paralyse a whole half of the body.
Coronal section through the thalamus: the internal capsule runs between the thalamus and caudate nucleus on one side and the putamen and globus pallidus on the other, Gray's Anatomy, 20th edition, 1918, figure 718Wikimedia Commons, Henry Vandyke Carter, Public domain (Gray718.png)
Sources
- Susan Standring (ed.), Gray's Anatomy, 42nd ed. (2020), chapter on the cerebral hemispheres.
- Arthur Guyton and John Hall, Textbook of Medical Physiology, 13th ed. (2016), ch. 56.
Prev: LanguageNext: The bridge between the halves