Meninges: Structure, Functions & Features

Meninges, singularly referred to as meninx has three membranous envelopes known as pia mater, arachnoid, and dura mater. These membrane layers protect and cover the spinal cord and the brain. Meninges also provide support to the nerves, blood vessels, lymphatics and cerebrospinal fluid surrounding your central nervous system. The cerebrospinal fluid fills the brain ventricles along with the space between the arachnoid and the pia mater. Cerebrospinal fluid and meninges both work together to protect our nervous system.

Key Terms: Meninges, Pia mater, arachnoid, dura mater, brain, spinal cord, nervous system, brain

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What are Meninges?

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Meninges are made up of 3 layers that protect the brain and spinal cord (central nervous system). The three layers of the meninges are –

1. Dura mater - This outermost layer of meninges is closest to the skull.
2. Arachnoid mater - This is the middle meninges layer.
3. Pia mater - This is the innermost layer that is closest to the brain tissue.

The arachnoid mater and pia mater are collectively known as leptomeninges.

Meninges

There are also spaces within the meninges. These spaces are –

a) Epidural Space

This space exists between the skull and dura mater and bones of the vertebral column and dura mater of the spinal cord.

b) Subdural space

The subdural space exists between the dura mater and the arachnoid mater. This space can be opened with a medical condition or in case of trauma to the brain as a brain bleed.

c) Subarachnoid space 

The subarachnoid space exists between the arachnoid mater and the pia mater. Subarachnoid space is filled with cerebrospinal fluid that protects the brain and spinal cord.

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Structure of Meninges

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The three layers of meninges are –

1. Pia Mater

The layer that tightly encloses the surface of the brain and spinal cord is known as the pia mater.

• Made up of fibrous tissue, the layer is filled with a flat layer of cells on the outside.
• Pia mater is filled with blood vessels travelling to the brain and spinal cord.
• It is separated from the arachnoid, a transparent and thin membrane, by the subarachnoid space.

2. Dura Mater

The outermost layer of the meninges, known as pachymeninx, is a strong, thick and dense membrane. 

• Dura mater is formed with dense fibrous tissue having flat cells covering the inner surface like the ones found in the pia mater and arachnoid.
• The layer surrounds the arachnoid and performs a lot of functions. 
• The dura mater supports the large venous channels, known as dural sinuses, carrying blood from the brain to the heart.

Dura Mater Infolding

The dura mater can be segmented into multiple septa supporting the meninges of the brain. 

In some places, the subdural space is absent, and intimately, the arachnoid is fused with the dura mater.

• The elongations of the arachnoid in walls of vast venous channels of the dura mater penetrate the dura mater as well as project in the veins.
• The walls of vast venous channels of the dura mater are a significant region where the fusion between two meninges takes place. 
• Here, the elongations of the arachnoid penetrate like fingers in the dura mater as well as project into veins. 
• The fingerlike arachnoids are also known as arachnoid granulations or arachnoid villi. 
• The cerebrospinal fluid passes through these projections on its way from the subarachnoid space to the dural space. 
• Spinal anaesthetics are also often introduced in the subarachnoid space.

Dura Mater Infolding

Arachnoid Mater

The middle element of meninges is the arachnoid mater or arachnoid membrane. It resembles a spider web, hence it is named as such. It is a transparent and thin membrane that cushions the meninges of the central nervous system. It is made up of fibrous tissue and its outer layer is packed with flat cells just like the pia mater, forming an arachnoid barrier.

The arachnoid appears like a loose fitting sac as it does not obey the surface convolutions of the brain. Whereas in the region of the brain high number of fine filaments called arachnoid trabeculae passes via from the arachnoid to blend with the tissues of the pia mater.

The arachnoid barrier does not have any extracellular collagen. It is considered a functional and morphological meningeal barrier that exists between the subarachnoid space and cerebrospinal fluid.

Leptomeninges

Leptomeninges is the name given to the pia mater and the arachnoid together. The word literally means "thin meninges". They are responsible for the beta trace protein production (prostaglandin D2 synthase). The beta trace protein is a major cerebrospinal fluid protein.

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Previous Year Questions

1. Which one of the following is the correct difference between rod cells and cone cells of our retina ?...[NEET 2008]
2. A sagittal section of the human brain is shown here. Identify at least two labels from A-D.... [NEET 2013]
3. Afferent nerve fibre carries impulses from...[NEET 1992]
4. Alzheimer's disease in humans is associated with the deficiency of...[NEET 2009]
5. Destruction of the anterior horn cells of the spinal cord would result in loss of...[NEET 2015]
6. Good vision depends on adequate intake of carotene rich food : Select the best option from the following statements...[NEET 2017]
7. Injury localized to the hypothalamus would most likely disrupt...[NEET 2014]
8. Myelin sheath is produced by….[NEET 2017]
9. Receptor sites for neurotransmitters are present on :…..[NEET 2017]
10. Injury to vagus nerve in human is not likely to affect...[NEET 2004]
11. A gymnast is able to balance his body upside down even in the total darkness because of..[NEET 2015]
12. Light rays entering the eye is controlled by...[NEET 1993]
13. What used to be described as Nissel granules in a nerve cell are now identified as...[NEET 2003]
14. Which part of the human ear plays no role in hearing as such but is otherwise very much required?….[NEET 2012]
15. Which part of the brain is responsible for thermoregulation …..[NEET 2019]

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Things to Remember

• Meninges are three layers in the brain that protects the brain and spinal cord.
• The delicate innermost layer of the meninges is the pia mater.
• The middle layer is like a web filled with fluid, it cushions the brain and is known as arachnoid.
• The tough outer layer is the toughest and is known as the dura mater.
• There are three spaces within the meninges - the epidural space, the subdural space, and the subarachnoid space
• The meninges acts as a support system for blood vessels that deliver blood to your central nervous system tissues, nerves lymphatics and cerebrospinal fluid.