Sir Isaac Newton described the laws of motion in 1687.
The first law of motion basically says
an object at rest will remain at rest until it is acted upon by an outside force
and an object in motion will continue in motion with the same speed and direction
unless acted upon by another force, which is called the Law of Inertia.
In simpler terms,
this means that there is a natural tendency of objects to keep on doing what they are doing.
All objects resist change in their state of motion.
Sir Isaac Newton's second law of motion basically says acceleration is produced when a force acts on a mass,
and the greater the mass of the object being accelerated,
the greater amount of force it will take to move it.
With these two general explanations of laws of physics,
let me show you what happens in a simple rear end car crash.
Before the moment of impact,
the person inside the car and the car itself are resting without motion.
as soon as the car is hit from behind
the mass and energy from the moving car begins to transfer energy into the stopped car.
What most people don't understand is that the body of the person sitting in the stopped car,
will NOT move immediately with, or as quickly, as the car they're sitting in.
But instead, there is a lag in time before their body starts to move.
In this graph, we have time going along the bottom, and G-forces are on the left.
The steel frame of the car being hit will begin to accelerate forward from the impact.
However, the person in the car will resist moving due to Newton’s law of Inertia.
What will happen is the vehicle will begin to move BEFORE the occupant.
The vehicle may actually move several inches forward
while the person's torso begins to increase pressure against the back of their car seat.
Note in this picture how the drivers hand is off the steering wheel.
Then the pressure from the seat shoots the torso of the human body forward like a diving board propels a diver.
The torso moves first.
And because your head is somewhat like a bowling ball supported only by your neck,
your head will remain motionless for a few more milliseconds.
So the car moves first, then your torso moves out from underneath your head.
This forces your head to suddenly have to accelerate to catch up with the car and your torso.
This very sudden acceleration of your head causes two points of stress in your neck.
The first stress point is at Cervical vertebrae C5 and C6
and the other stress point is between Cervical vertebrae C1 and C2.
These two areas of our neck usually get the most damaging forces which often times tears
or permanently stretches the ligaments that hold our vertebreas in their proper place.
It is these exact same laws of physics that cause mild traumatic brain injuries.
Our brain is very complex and is made up of two different types of brain cells.
The center of our brain is called “white brain matter”
and then there is the “grey brain matter” which surrounds the white matter.
Our brains are floating in a liquid, which is cerebral spinal fluid, all housed inside our very hard skull.
It is important to know that the white brain matter is much more dense and heavier than the grey brain matter.
And there are billions of cells in our brains, and there are Axons that connect the white and grey matter.
These Axons transmit information from one part of the brain to another.
When a person is suddenly hit from behind, like in our example,
your head, which is the last part of your body to move in a crash,
has to accelerate forward quickly to catch up to the car and your torso,
and your head may even be hit on the back by your head rest further increasing the acceleration of your head.
Since our brain is floating in liquid and consists of two different types of brain cells,
one heavier than the other, each part of the brain accelerates at a slightly different time and rate.
The difference in the movement between the white and grey matter causes "diffuse axonal shearing".
This is a medical term that explains how the connecting Axons
are damaged from the shearing between the grey and white brain cells.
Your brain cells follow Newton's first law of physics
and our brain remains still while the skull is being accelerated forward by the headrest.
The brain’s grey matter is accelerated first because it is closest to the back of our skull,
and it is softer, and has less density than the white brain matter.
The pressure from the grey brain matter begins to apply force to the white brain matter,
and then the white brain matter begins to move to catch up with the grey matter.
Now, as your head is traveling forward,
it will suddenly stop when your seat belt which holds your torso in your seat,
causes your head to jerk backwards.
Meanwhile, your brain is still moving forward in your skull, and goes through the same traumatic forces a second time.
Again, this causes shearing of the axons, as the grey and white matter move at different times and speeds.
Also, if there is some rotation of your head,
like if your head is slightly turned before or during the crash,
then the shearing to your brain cells can be even worse.
This type of an injury can happen in less than a quarter of a second.
Most times, people don’t even lose consciousness.
They may not even have a bump on the back of their head.
But they may feel dazed, groggy, confused, agitated,
or experience many other feelings from this traumatic brain injury.
Unfortunately, many mild traumatic brain injuries go undiagnosed.
It is not uncommon for people to feel an adrenaline rush into the bloodstream,
and due to the chaos associated with a crash,
they may think they are okay and not seek immediate medical care,
even though they have just experienced a very life changing injury.
In my experience,
the injured person is usually the last one to realize or know that they have suffered a mild traumatic brain injury.
It is usually their family or friends who notice that they are having a difficult time
selecting words in a conversation or being able to concentrate or remember things.
Normal x-ray, CT scan or MRI will not show a mild brain injury because our brain cells are so small.
These tests are good at showing the anatomy of our brains, but not our brains inability to function.
Instead of the basic radiological studies,
doctors must use more sophisticated tests to measure the function or lack of function of our brain.
They can use specialized MRI’s with the DTI which stands for Diffusion Tenser Imaging,
or SWI which stands for Susceptibility Weighted Imaging.
Your doctors may even order a CT pet scan which can measure how your brain cells are functioning
by measuring the amount of sugar your brain cells are using.
If certain brain cells are not using sugar because the cells are damaged,
a CT-SPECT scan will show this loss of brain function.
In this image, the blue areas in the brain are damaged cells.
There are other tests that also measure brain function and they include spect scans
and a MEG which stands for Magnetoencephalography
which is one of the most sensitive ways to measure brain function.
In addition to the radiological tests and studies that can be used to measure a person's brain function,
there is also neuropsychological testing which measures brain performance.
Neuropsychologists are trained experts in assessing the function of the brain
through administering psychological tests.
These tests require us to use different parts of our brain in different ways,
and if we have a deficit, it will show up in the testing.
As you can see,
a mild traumatic brain injury is an extremely serious injury,
and it requires extremely sophisticated testing,
as well as very good doctors to appreciate and understand
when someone may be suffering from such an injury.
I hope you have found this information helpful and if you have more questions about brain injuries,
please call me.
Thank you for watching my video.