<p>This is a simple logic to understand. 
In the brain the grey matter is on the cotex.Grey matter is a tissue made of the cytons due to which the cotex is pinkish Grey in colour. The White matter,the tissue made of axons is inside to the brain.
   Cortex is the processing centre which has cytons. In the spine the processing is to be done internally. So the cytons concentrate inside the spine which we call the Grey matter.Similarly the axons are to be around the Grey matter to transfer messages from and to other organs.They form the White matter outside the spine.</p>

CC BY-SA 3.0
2016-01-04T01:39:41.733Z
2016-01-04T01:39:41.733Z
Krishna teja.
<p>I'll tackle this question from a <strong>functional</strong> point of view. </p>

<p>Gray matter are cell bodies, white matter are myelinated fiber tracts.</p>

<p>In the brain, the gray matter is basically the cortex, the white matter lies mainly underneath it. The Cortex is the place where all the higher mental <strong>processing</strong> takes place (Fig. 1).</p>

<p><img src="https://i.sstatic.net/YrwUI.jpg" alt="cortex"><br>
<sup>Fig. 1. Cortical functions. Source: <a href="http://www.pennmedicine.org/health_info/body_guide/reftext/html/nerv_sys_fin.html" rel="nofollow noreferrer">Penn Medicine</a></sup></p>

<p>The white matter in the brain connects the various parts of the cortex so that information can be transported for further processing and integrated.</p>

<p><img src="https://i.sstatic.net/wjtYo.jpg" alt="white matter"><br>
<sup>Fig. 2. Central white matter. Source: <a href="http://www.nlm.nih.gov/medlineplus/ency/article/002344.htm" rel="nofollow noreferrer">NIH Medline</a></sup></p>

<p>Since the cortex is the 'processor', it makes sense to connect the parts subcortically (more efficient as it leads to shorter connections). However, the cortex has been expanding very late in evolution, so this 'endpoint reasoning' can be contested, because from an evolutionary perspective, more cortex was needed and hence it was expanded right where it happened to be, namely in the outer part of the brain.</p>

<p>In the spinal chord things are pretty much reversed; grey matter within, white matter around it (Fig. 3). </p>

<p><img src="https://i.sstatic.net/XESUZ.jpg" alt="gray white matter spinal chord"><br>
<sup>Fig. 3. Section through spinal chord with central grey matter and surrounding white matter. Source: <a href="http://www.med.umich.edu/lrc/coursepages/m1/anatomy2010/html/modules/NS_overview_module/NS_Overview_07.html" rel="nofollow noreferrer">University of Michigan</a></sup></p>

<p>The white matter, again, is formed by various tracts (Fig. 4) and the grey matter with parts that are processing information (fig. 5). </p>

<p><img src="https://i.sstatic.net/mkYNf.png" alt="spinal tracts"><br>
<sup>Fig. 4. Section through spinal chord showing the spinal tracts forming the white matter. Source: <a href="https://biology.stackexchange.com/questions/2864/spinal-cord-do-the-axons-from-white-matter-synapse-with-the-cell-bodies-in-grey">Biology.SE</a></sup></p>

<p><img src="https://i.sstatic.net/E24eh.jpg" alt="Spinal reflex archs"><br>
 <sup>Fig. 5. Section through spinal chord showing the spinal reflex arches forming the gray matter. Source: <a href="http://www.apsubiology.org/anatomy/2010/2010_Exam_Reviews/Exam_4_Review/CH_12_Internal_Anatomy_of_the_Spinal_Cord.htm" rel="nofollow noreferrer">APSU Biology</a></sup></p>

<p>The white matter in the spinal chord constitutes the various sensory and motor pathways to and from the brain, respectively. The gray matter constitutes basic processing nuclei that form the reflex arches in the spinal chord. These reflex arches process incoming sensory information (e.g. pain) and govern motor output (e.g., pulling the hand away from the fire). </p>

<p>Again, the structure makes sense in terms of efficiency, as the reflex arches combine the sensory and motor tracts to govern reflexes, and therefore processing them from within saves space.  </p>

CC BY-SA 3.0
2015-05-26T12:43:45.740Z
2015-05-26T12:52:05.040Z
2017-04-13T12:48:14.127Z
AliceD
<p>In the brain proper, grey matter forms the outer layer of the brain, and white matter forms the inner layer. In the spine, this is reversed: white matter forms the outer layer of the spine, and grey matter the inner layer. Is there a developmental or functional reason for this?</p>

<neuroscience><neuroanatomy>
Why is the order of white/grey matter different in the brain and spinal cord?
RECURSIVE FARTS
# Why is the order of white/grey matter different in the brain and spinal cord?

(Asked by: username_0 on 2015-05-25)

In the brain proper, grey matter forms the outer layer of the brain, and white matter forms the inner layer. In the spine, this is reversed: white matter forms the outer layer of the spine, and grey matter the inner layer. Is there a developmental or functional reason for this?

**Tags:** neuroscience, neuroanatomy


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## 2 answers

### Answer by username_2 on 2015-05-26. Score: 9 | Accepted answer

I'll tackle this question from a **functional** point of view.

Gray matter are cell bodies, white matter are myelinated fiber tracts.

In the brain, the gray matter is basically the cortex, the white matter lies mainly underneath it. The Cortex is the place where all the higher mental **processing** takes place (Fig. 1).

![cortex](https://i.sstatic.net/YrwUI.jpg)  
Fig. 1. Cortical functions. Source: [Penn Medicine](http://www.pennmedicine.org/health_info/body_guide/reftext/html/nerv_sys_fin.html)

The white matter in the brain connects the various parts of the cortex so that information can be transported for further processing and integrated.

![white matter](https://i.sstatic.net/wjtYo.jpg)  
Fig. 2. Central white matter. Source: [NIH Medline](http://www.nlm.nih.gov/medlineplus/ency/article/002344.htm)

Since the cortex is the 'processor', it makes sense to connect the parts subcortically (more efficient as it leads to shorter connections). However, the cortex has been expanding very late in evolution, so this 'endpoint reasoning' can be contested, because from an evolutionary perspective, more cortex was needed and hence it was expanded right where it happened to be, namely in the outer part of the brain.

In the spinal chord things are pretty much reversed; grey matter within, white matter around it (Fig. 3).

![gray white matter spinal chord](https://i.sstatic.net/XESUZ.jpg)  
Fig. 3. Section through spinal chord with central grey matter and surrounding white matter. Source: [University of Michigan](http://www.med.umich.edu/lrc/coursepages/m1/anatomy2010/html/modules/NS_overview_module/NS_Overview_07.html)

The white matter, again, is formed by various tracts (Fig. 4) and the grey matter with parts that are processing information (fig. 5).

![spinal tracts](https://i.sstatic.net/mkYNf.png)  
Fig. 4. Section through spinal chord showing the spinal tracts forming the white matter. Source: [Biology.SE](https://biology.stackexchange.com/questions/2864/spinal-cord-do-the-axons-from-white-matter-synapse-with-the-cell-bodies-in-grey)

![Spinal reflex archs](https://i.sstatic.net/E24eh.jpg)  
Fig. 5. Section through spinal chord showing the spinal reflex arches forming the gray matter. Source: [APSU Biology](http://www.apsubiology.org/anatomy/2010/2010_Exam_Reviews/Exam_4_Review/CH_12_Internal_Anatomy_of_the_Spinal_Cord.htm)

The white matter in the spinal chord constitutes the various sensory and motor pathways to and from the brain, respectively. The gray matter constitutes basic processing nuclei that form the reflex arches in the spinal chord. These reflex arches process incoming sensory information (e.g. pain) and govern motor output (e.g., pulling the hand away from the fire).

Again, the structure makes sense in terms of efficiency, as the reflex arches combine the sensory and motor tracts to govern reflexes, and therefore processing them from within saves space.


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### Answer by username_1 on 2016-01-04. Score: 0

This is a simple logic to understand.
In the brain the grey matter is on the cotex.Grey matter is a tissue made of the cytons due to which the cotex is pinkish Grey in colour. The White matter,the tissue made of axons is inside to the brain.
Cortex is the processing centre which has cytons. In the spine the processing is to be done internally. So the cytons concentrate inside the spine which we call the Grey matter.Similarly the axons are to be around the Grey matter to transfer messages from and to other organs.They form the White matter outside the spine.


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