Today we will look at the layer of supportive and protective tissue that separates the skull and the brain.
The main functions of the meninges include:
- Protecting the brain and spinal cord form mechanical injury
- Providing blood suply to the skull and to the hemispheres
- Providing a space for the flow of cerebrospinal fluid.
This layer of protective tissues is collectively named the “meninges” but is actually composed of 3 main layers: The Dura mater, the Arachnoid layer, and the Pia mater.
The Dura Mater
The dura mater is the toughest and outermost layer of the meninges. If you have the chance to dissect a real brain, you will notice that the dura mater is indeed quite strong.
The Dura mater can be divided into two layers:[unordered_list style=”arrow”]
- The endosteal layer: This is the thickest layer and it lines the skull.
- The meningeal layer: This layer lines the endosteal layer most of the time, except in a few places such as the falx cerebri and the tentorium cerebelli. At these places, the meningeal layer actually separates from the endosteal layer and “sinks down” between the left and right hemishpere for the falx cerebri, and between the occipital cortex and the cerebellum for the tentorium cerebelli.
Here is a hint for remembering what “tentorium cerebelli“ stands for: The word “tentorium” comes from the word “tent.” You can visualize those old tents that had the curved shape of Chinese temple roofs. If you look at the brain and the cerebellum from the back, you will see that the space in between them kinda looks like that shape… Thus giving “tent of the cerebellum”, or “tentorium cerebelli” in latin.[/box]
As it “sinks down” the meningeal layer creates a space between the endosteal layer . This space can house the sinuses.
2 Interesting Facts About The Dura Mater:
- The dura mater has it’s own blood supply that comes from a set a meningeal arteries, the main one being the middle meningeal artery.
- The dura mater is pain sensitive. Yes, the rest of the brain is not sensitive whatsoever, but the dura mater is innervated by trigeminal nerves (mostly).
The Arachnoid layer
The layer right under the dura mater is called the arachnoid. If “arachnoid” makes you think of spiders, you are in the right direction. The arachnoid layer is actually filled with a intricate “web” of collagen.
I like to think of this layer as a sort mattress filled with collagen instead of springs, that dampens any shock the layer may receive.
The innermost layer is called the pia mater. But right in between the arachnoid layer and the pia mater, there is “a space” named the “subarachnoid space.” This subarachnoid space houses the brain’s cisterns (“pools” of Cerebro Spinal Fluid) as well as cerebral arteries and veins.
The Pia Mater
The pia mater is the innermost layer lining the brain. In fact, it completely lines every sulci and gyri of the hemispheres, contours the brainstem, and all the folds of the cerebellum. It is very tender (“pia” means “tender” in latin) and is very easily damaged while performing dissections.
The pia mater also plays a role in the formation of the choroid plexus (for the lateral, 3rd and 4th ventricles).
Together the arachnoid layer + the pia mater are called the leptomeninges.
Minimum to remember:[unordered_list style=”tick”]
- There are 3 layers of protection and support between the brain and the skull: The Dura mater, the arachnoid layer, and the pia mater.
- The dura mater is the “toughest” layer, and the pia mater is the “softest” layer.
- The arachnoid layer is filled with a web of collagen.
- All together these three layers are called the meninges.
- The arachnoid layer + pia mater layer is called the leptomeninges.
If you want more articles and videos about the Nervous System, you can find them here. More resources are available to help make Biology fun. I invite you to absorb all the content you can find here at Interactive-Biology.com.