Gabby Plata

Gabby has one younger sister and a dog named Granola who kind of looks like a cow. She has a very big interest in STEM and even attended the Academy for Science and the Arts in Des Plaines for some…

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Meninges and PBI

Abstract:

The meninges form 3 tiers of fibrous tissue known as wrappers that envelop and protect the central nervous system. In regard to penetrative brain injury (PBI), “the external part of the dura, the periosteal (dura mater) layer, is tightly fixed to the skull.” (Decimo. I, 2012). Meaning both the skull and the meninges work together to protect the brain from penetration. Besides the skull, the dura mater is the first to encounter penetration when suffering from a PBI because it is the outermost layer of the meninges and is faced with foreign objects first. This report explores the density and strength of the meninges without the added protection of the skull. The results indicate that the glad wrap, replicating the role of the meninges is not able to resist forces above 0.09634 newtons. The 0.5% and 1% agarose gel and glad wrap emulating white, grey matter and the meninges respectfully cannot handle a weight of 24.6g or higher because penetration occurred in all three layers in every test (figure 1). The amount of force the meninges can withstand pales in comparison to the skulls withstanding force of 2400 newtons. However, due to the close proximity of the two, the meninges do not need to be able to withstand great amounts of force. Suggesting a symbiotic relationship between the meninges and the skull. The two are structured to complement the other in order to protect the brain from both PBI’s and TBI’s simultaneously.

Background:

“Penetrating injury to the brain occurs from the impact of a bullet, knife or other sharp objects that force hair, skin, bones, and fragments from the object into the brain.” (Brain injury alliance; 2005). Penetrating Brain Injury (PBI) is less common than other traumatic brain injuries (TBI) such as concussions but has a very high mortality rate of 91%. Those that do survive PBI have reduced cognition caused by the rupture of neurons within the brain. PBI is often associated with intracranial hemorrhage, edema, ischemia and a high risk of infection. The meninges form 3 tiers of fibrous tissue known as wrappers that envelop and protect the central nervous system. Combined with cerebrospinal fluid, the meninges act as a shock absorber of TBI’s with blunt objects by acting as a stabilizer. However, in regard to penetration, “the external part of the dura, the periosteal (dura mater) layer, is tightly fixed to the skull.” (Decimo. I, 2012). Meaning both the skull and the meninges work together to protect the brain from penetration. It has been documented that the skull can withstand 2400 newtons (Journal of Neurosurgery, 2012) of force. The role of the meninges in preventing PBI is relatively unknown due to the connection between the dura mater and the overshadowing strength of the skull. This report explores the density and strength of the meninges without the added protection of the skull.

Aim:

To determine the impacts of brain penetration at various forces.

Hypothesis:
As the force of penetration increases (IV), the damage to the brain and meninges (DV) will increase.

Apparatus:

• One pen

• 3X 100g 0.5% agarose concentration

• 3X 100g 1% agarose concentration.

• 3X 30ml lab containers

• A roll of glad wrap

• A set of varying weights: 20g, 50g, and 100g.

• Sticky tape

• Ruler

Method:

1. Combine the two cubes of agar into a lab container by placing the agar gel cube with the higher concentration (1%) of agarose on top of the cube with the lower concentration (0.5%). Repeat twice more to have a total of three agar filled lab containers.

2. Fix a tight membrane of glad wrap over the top of the container, sealing the contents inside.

3. Fix a 20g weight to the blunt end of the pen with sticky tape, leaving the sharp end exposed.

4. Drop the pen from a height of 43cm onto a container containing the agarose concoction.

5. Record using qualitative methods such as photos and visual observations detailing the impact the pen has on the agarose.

6. Repeat steps 2–5 replacing the 20g weight increasing size; 50g first and then 100g. Pierce a different agarose concoction each time.

Results:

Figure 1:

20g weight (Combined mass of 24.62g)

Glad wrap: Clean penetration

1% Agar: Clean penetration

0.5% Agar: Clean penetration

Depth of object (cm): 7

Force of object (N): 0.0963

50g weight (Combined mass of 54.62g)

Glad wrap: Clean penetration

1% Agar: Clean penetration

0.5% Agar: Clean penetration

Depth of object (cm): 7

Force of object (N): 0.2137

100g weight (Combined mass of 104.62g)

Glad wrap: Clean penetration

1% Agar: Clean penetration

0.5% Agar: Clean penetration

Depth of object (cm): 7

Force of object (N): 0.4094

Discussion:

The results suggest that the 0.5% and 1% agarose gel and glad wrap emulating white and grey matter and the meninges respectfully cannot handle a weight of 20g or higher because the sharp object penetrated all three layers in every test (figure 1).

In test 1, all three layers were penetrated indicating that the force of the penetration was greater than the resistance of the meninges. According to Newton’s second law, a 20g weight with an added 4.6g from the additional pen under the influence of gravity with an acceleration of 9.8m/s/s reaches a force of 0.09634 newtons. (figure 1). This indicates that the meninges are unable to withstand a force of 0.09634 newtons, leading to its penetration, and the agar beneath it. The agar could also not withstand this force, as both layers were penetrated.

Results were similar in tests 2 & 3, figure 1 indicates that the glad wrap, 1% and 0.5% agar suffered a clean penetration. Test 2 had a weight of 50g, with a total mass of 54.6g, a force of 0.53508 newtons and penetrated all layers. Test 3 had a weight of 100g, with a total mass of 104.6 and a combined force of 1.02508 newtons.

These results indicate that the glad wrap, replicating the role of the meninges is not able to resist forces above 0.09634 newtons. Therefore, the meninges were unable withstand forces above or equal to 0.09634 newtons.

The primary function of the meninges is to envelop and protect the CNS, the most important part of this function in the meninges is the Dura mata. Which contains strong tissue enabling it to withstand forces from many directions due to the criss crossing of collagen bundles. Besides the skull, the Dura Mata is the first to encounter penetration when suffering from a PBI because it is the outermost layer of the meninges and is faced with foreign objects first. In the experiment, the meninges are emulated by the glad wrap covering the container. Figure 1 indicates that the glad wrap was unable to resist penetration of any force, the lowest being 0.09634 newtons. While the primary role of the meninges is to protect the CNS, it is foreshadowed by the skull, that is able to withstand 2,400 newtons (Journal of Neurosurgery, 2012). The presence of the skull could play a role in the meninges inability to withstand large forces and so structurally, forms an impermeable barrier cutting the brain off from harmful infections in the cranium that may have entered through the skin.

The amount of force the meninges can withstand pales in comparison to that of the skull. However, due to the close proximity of the two, the meninges do not need to be able to withstand great amounts of force. Allowing for the meninges to adapt its structure to be better suited for other purposes, such as circulating cerebrospinal fluid (CSF) giving the brain some stabilisation when encountering a TBI with a blunt object by providing some empty space for the brain to counterbalance an impact. This suggests a symbiotic relationship between the meninges and the skull. The two are structured to complement the other in order to maintain a functioning brain.

A fully developed human skull is able to withstand 2,400 newtons while the meninges were unable to withstand 0.09634 newtons. The skull plays a key role in protecting the brain and is the first line of defence from TBI. On occasion the skull can be damaged, leading to increased exposure of the brain and the meninges. This is especially important during baby development up to 18 months. “TBI is the leading cause of death and disability in children” (Journal of medicine and life, 2011). This is because infant skulls are still developing up to 18 months and haven’t yet reached the capacity to withstand the forces of a fully developed skull. The skulls reduced ability to withstand pressure, leads to children having a higher mortality rate due to TBI’s.

According to figure 1, all tests had a clean penetration through the glad wrap and agarose solutions. This is an example of a ‘through and through’ injury, which occurs when an “object enters the skull, goes through the brain, and exits the skull.” (Brumback R, 1996). While the objects did not exit the brain, their path was hampered by the bottom of the container. Had the bottom of the container been removed prior to the experiment, the whole of the object would have likely passed cleanly through the meninges, and agarose solutions. Through and through injuries are most common in cases involving gun violence, leading to a 91% mortality rate (Center for Disease Control, 2002).

It has to be acknowledged however, that the density and resistance of glad wrap does not 100% emulate that of the meninges. This accounts for some decreased reliability and validity within the experimental design. Additionally, the force of impact with the container was too high to yield any tangible results. In order to improve the experiment to yield tangible results, it is advisable to reduce the amount of force being placed upon the meninges. This can be done by lowering the height the pen is dropped from 43cm to 10cm, the weights could be reduced to a set of 5g, 10g, and 20g.

Additionally, to better emulate the environment of the brain within the container, water could be introduced to emulate CSF circulating around the white and grey matter within the brain. This could help absorb some of the impact if the glad wrap seal were to be penetrated.

Conclusion:

The results seemed to suggest that as the force of penetration increases, the damage to the brain and meninges will maintain because all test results showed no qualitative increase in damage of the containers of agarose the hypothesis is proved inconclusive: As the force of penetration increases (IV), the damage to the brain and meninges (DV) will increase. However, further experimentation must be done by reducing the force of impact upon the glad wrap, and hence reaching some tangible data.

Gabby Plata

Meninges and PBI

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