What is the Difference Between Cranial and Spinal Meninges

The main difference between cranial and spinal meninges is that cranial meninges are the protective coverings of the brain, consisting of channels in the dura mater between various parts of the brain called dural folds, whereas spinal meninges are the protective coverings of the spinal cord whose dura mater acts as a dural sheath. Furthermore, cranial meninges contain two layers in the dura mater while the spinal meninges contain a single layer in the dura mater. In addition, cranial meninges may not produce an epidural space while spinal meninges produce an epidural space filled with fat. 

Cranial and spinal meninges are two types of meninges; these are the protective coverings of the central nervous system. Generally, they are composed of three connective tissue layers from the outwards to the inwards: dura mater, arachnoid mater, and pia mater. 

Key Areas Covered 

1. What are Meninges
     – Definition, Anatomy, Function
2. What are Cranial Meninges
     – Significance
3. What are Spinal Meninges
     – Significance
4. What are the Similarities Between Cranial and Spinal Meninges
     – Outline of Common Features
5. What is the Difference Between Cranial and Spinal Meninges
     – Comparison of Key Differences

Key Terms

Arachnoid Mater, Cranial Meninges, Dura Mater, Pia Mater, Spinal Meninges

What are Meninges 

Meninges are the protective outer covering of the brain and the spinal cord. Generally, they contain three connective tissue layers: dura mater, arachnoid mater, and pia mater. In addition, three spaces occur between the three layers: epidural space, subdural space, and subarachnoid space.  

Dura Mater 

Basically, the dura mater is the outer layer, which is thick, dense and fibrous. Also, it is quite inelastic. In addition, the epidural space occurs between the superior surface of the dura and the protective bone layer. On the other hand, subdural space occurs between the dura mater and the arachnoid mater.  

Arachnoid Mater 

Arachnoid mater is the middle layer, which is a delicate web of avascular tissue involved in the cerebrospinal fluid (CSF) metabolism. It also consists of three layers. They include the mesothelial layer, which is superficial, the central layer, which contains cells conjoined by many junction proteins, and a deep layer with loosely packed cells and many collagen fibers. In addition, clusters of arachnoid villi protrude into the dura mater, serving as a network of communication. Moreover, subarachnoid space occurs between the arachnoid and pia mater. It is filled with CSF. Here, the primary function of CSF is to cushion the brain from trauma, while supplying oxygen and nutrients and removing wastes. Therefore, major arteries of the brain run through the subarachnoid space. 

Pia Mater 

The pia mater is the innermost layer, lying closely over the brain. It is thin and highly vascular, aiding the supply of oxygen and nutrients to the brain and the spinal cord. Unlike the arachnoid mater, the pia mater follows the contours of the sulci and gyri. Moreover, there are two layers of pia mater: epipial layer or the outer layer, which contains collagen fibers and the intima pia or the inner layer, which contains elastic and reticular fibers.  

What are Cranial Meninges 

Cranial meninges are the protective outer coverings of the brain. The superior surface of the dura potentially lies the epidural space by securely attaching to the periosteum of the skull. However, an epidural space in the cranial meninges can occur pathologically. Furthermore, the two layers of the dura are the periosteal layer, which is closest to the calvarium, and the meningeal layer, which occurs towards the inside. However, these two layers mostly occur fused other than in venous sinus and dural reflections or folds. 

Figure 1: Cranial Meninges

Furthermore, venous sinuses are the channels complexes which form a branching network to collect oxygen-depleted blood from the brain. On the other hand, dural reflections are the places where the meningeal layer descends into the cranial cavity, forming the septa with two, face-to-face meningeal layers. In addition, the falx cerebri and the tentorium cerebelli are the two main dural reflections. Moreover, subdural space occurs between the meningeal layer and the arachnoid mater. It is also a potential space, which only exists under pathological conditions. Meanwhile, the arachnoid mater of the cranial meninges does not follow the contours of the cortical sulci but, it bridges them. Arachnoid trabeculae protrude into the subarachnoid space. 

What are Spinal Meninges 

Spinal meninges are the protective outer coverings of the spinal cord. Generally, they extend from the foramen magnum to the filum terminale. They also occur separately from the wall of the vertebral canal. Here, the forming space is the epidural space, filled with loose connective tissue and the internal vertebral venous plexus. Furthermore, spinal nerves origins from the vertebral canal, piercing the dural mater. Therefore, the dura mater surrounds the root of the spinal nerve. Same as the epidural space, spinal meninges contain a subdural space as well.

Figure 2: Spinal Meninges

Furthermore, the spinal cord ends up at the L1 and L2 levels, forming a tapered end called conus terminalis. However, the subarachnoid space expands up to filum terminale, forming the lumbar cistern. Also, the pia mater fuses with the filum terminale. Pia mater forms the denticulate ligaments between nerve roots by becoming thick.  

Similarities Between Cranial and Spinal Meninges 

• Cranial and spinal meninges are the two types of meninges which serve as protective outer coverings of the central nervous system. 
• They occur just below the bone. 
• They contain three connective tissue layers: dura mater, arachnoid mater, and pia mater. Also, leptomeninges refer to the arachnoid mater and pia mater collectively. 
• Both contain subarachnoid space filled with cerebrospinal fluid, which acts as a cushion, preventing direct damage to the brain. 
• Their main function is to provide a supportive framework to the cerebral and cranial vasculature. 
• Moreover, they act along with the cerebrospinal fluid to protect the central nervous system from mechanical damage. 

Difference Between Cranial and Spinal Meninges 

Definition 

Cranial Meninges refer to the part of meninges which serve as the protective outer coverings of the brain while the spinal meninges refers to the part of meninges which serve as the protective outer covering of the spinal cord. 

Occurrence 

While cranial meninges mainly surround the skull, the spinal meninges are a prolongation from the skull to the S2 level of the sacrum. 

Epidural Space 

Moreover, cranial meninges may not produce an epidural space while spinal meninges produce an epidural space filled with fat.  

Dural Meter 

Cranial meninges contain two layers in the dural mater while spinal meninges contain a single layer in the dural mater.  

Folds of the Dura Mater 

Furthermore, cranial meninges make folds in the dura mater between various parts of the brain while the dura mater of the spinal meninges forms a dural sheath. 

Subdural Space 

Cranial meninges do not contain a subdural space while spinal meninges contain a subdural space. 

Arachnoid Trabeculae  

In addition, cranial meninges contain arachnoid trabeculae in the subarachnoid space while spinal meninges contain arachnoid trabeculae condensed into the posterior median septum.  

Conclusion 

Cranial meninges are the protective covering of the brain, occurring just below the skull. Significantly, the dural mater of the cranial meninges contains folds between various parts of the grain. Their dural mater contains two layers: periosteal layer and meningeal layer. Besides, the arachnoid trabeculae occur in the subarachnoid space in the cranial meninges. In contrast, spinal meninges are the protective coverings of the spinal cord. However, they contain an epidural space filled with fat. A single dural mater layer occurs in the spinal meninges. On the other hand, their arachnoid trabeculae are condensed into the posterior median septum. Therefore, the main difference between cranial and spinal meninges is their anatomy.   

References:

1. Ghannam JY, Al Kharazi KA. Neuroanatomy, Cranial Meninges. [Updated 2019 Mar 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available Here.
2. Bath, Mike. “The Spinal Cord.” TeachMeAnatomy, 28 Sept. 2019, Available Here.

Image Courtesy:

1. “1316 Meningeal LayersN” By OpenStax (CC BY 4.0) via Commons Wikimedia   
2. “Gray770-en” By Mysid – Made by Mysid Inkscape, based on plate 770 from Gray’s Anatomy (Public Domain) via Commons Wikimedia