Neurobiology of Concussion - Part 3

Part 1 - Quick anatomy lessons

Part 2 - How the brain is organized

Part 3 - The effects of a concussion injury

Part 4 - Symptoms explained


How does this information help me?

In our first two articles of this series we reviewed a little of the anatomy and structure of the brain and nervous system.  We’ve outlined this information for you because we believe knowing more will help you get better faster and encourage smart choices in your recovery.  

Article Overview

This is a heavy article, so read as much or as little as you please. To summarize, concussions are not simple injuries. A lot of things happen during and after a concussive event that result in symptoms, including:

  • Injury to the brain tissues
  • Biochemical and electrical changes in the brain and brain cells
  • Changes in the connectivity and activation of brain areas
  • Changes in blood flow and the transport of energy and oxygen
  • Changes in how the brain makes and uses energy
  • Inflammation
  • Injury to your neck, vestibular system or other nerves that can cause symptoms
Keep in mind that the effects of concussion are temporary and improve over time in most cases.  Some issues might require a bit more help and guidance  to make better. Not all of these things happen in every injury, and in some cases your brain might not be affected even if you have symptoms (for example with a neck or vestibular injury).

 

What happens to the brain:

It’s hard to know exactly what happens to a brain during a concussion-injury because there’s no good way to really “get inside the head” when it’s happening.  But, what we think happens is a sort of clumsy dance of the brain inside your skull:

In some brain injuries a contusion (“brain bruise”) or hemorrhage (“brain bleed”) can happen which means blood vessels have been damaged in that area. Skull bones might also be injured if the impact is strong enough. Contusions, hemorrhages and skull fractures are not a normal part of concussions and it’s important to see a doctor to rule them out.

  • Brains move- Because brains do have a few millimeters to move inside the skull, an impact or very quick movement may cause movement of the brain.  
  • A brain might bump into the inside of your skull -  In some cases this might cause mild injury to the brain tissue.

  • Brain tissue and brain cells get strained and stretched - More recent research is suggesting that the brain is actually stretching and changing shape during an concussive event.  Brain tissue is flexible, but if it stretches too much there can be changes to important brain connections and injury to brain cells (neurons).  

    • The stretching forces might be strongest in the middle of the brain, which means any part of the brain can be affected during a concussion (not just the outside).

    • Stretching and straining might explain much of the damage we see during concussion because it causes tiny microscopic injury to brain cells. But this damage is so small that we can’t see it on medical imaging - sort of like with a sore muscle after exercise.

Many videos about concussion show a brain made of jello  “sloshing” and “scrambling” inside a skull - which can be a scary and unhelpful sight.  While our brains are soft and delicate,  they are tougher than jello and also have an ability to repair themselves similar to the rest of your body.

 

 

NEUROMETABOLIC CASCADE OF CONCUSSION

In concussion science, the biochemical changes that happen after injury are referred to as the neurometabolic cascade.  The basic process happens like this:

  1. Stretching and squishing of the brain during injury causes damage to individual brain cells (neurons).  Neurons have “skeletons’ (cytoskeletons) and membranes that get damaged.

  2. Important ions and neurotransmitters spill out of brain cells.  The injured cells don’t work very well because of this spillage, and damage to their cytoskeletons.

  3. Affected brain cells work really hard to clear up the spills which uses up a lot of energy.  These cells also can’t make energy very well because their energy factories (mitochondria)  are affected by calcium inside the cell.

  4. Injured brain cells  have a tough time communicating with other brain cells.  Some brain cells might even lose connections.  The protective myelin coating around neurons might also stop working so signals are also slowed.

  5. Overall brain networks aren’t working very well and there is a change in the chemistry of the brain which takes time to return to normal.  Cells are using up more energy than normal too so tend to get tired more easily.

What can we say? It's complicated... 

What can we say? It's complicated... 

Inflammation

All this action triggers immune cells in the brain to try and clean up the issues which leads to an inflammatory response.  Immune cells get stimulated and release chemicals (cytokines) that are meant to repair injury.  

 

Blood flow changes

Studies have shown that blood flow also changes in the brain in response to injury, going through cycles of reduced blood flow.  Blood flow and pressure in different areas of the brain changes, which affects how well those areas are working.  

 

Genetics

There are even genetic changes that happen due to injury which include expression of genes involved in inflammation, metabolism and cell repair.  The point here is that concussion and brain injuries affect you even at the level of expression of DNA!

 

In summary:

When you experience a concussion there are many important changes that happen in the brain.  As a result of these changes, some brain cells are damaged and don’t work well.  Some brain areas and networks are less active and the brain is also using up way more energy and tires out more easily.  These brain changes are most profound for about 7-10 days after injury so that’s why we’re so careful about minimizing risk of re-injury especially during this window.  Keep in mind that some changes might persist longer.

neurometabolic-cascade-vulnerability.jpg

BUT WAIT THERE’S MORE:What happens in the neck?

Now that’s we’ve explored the brain in more detail, let’s move on to the neck.  What many people don’t know is that a neck injury (sometimes called cervical injury) can cause very similar symptoms to a brain concussion injury (see Table 1 below).  In many cases, both the brain and the neck are injured - but there may be cases where just one is hurt.

Notice how many symptoms are shared in common.  From Cheever et al. 2016.

Notice how many symptoms are shared in common.  From Cheever et al. 2016.

The neck can be injured during the same types of impacts that cause concussion (which is no surprise since the head and neck linked together).  Impacts, falls or quick movements of the head (like in whiplash injury) can harm the muscles and nerves in your neck.  

We also want to be on the lookout for any potential bone or nerve injury in the neck too - which your doctor or medical team will investigate and rule out.

The muscles and nerves in your neck help your brain keep track of where your head and neck are positioned and are important parts of your vestibular system.  Your brain relies on this information to stabilize posture and eye movements and  keep you balanced. Neck injury can cause that system to work less effectively, which leads to dizziness or vertigo, headache, trouble balancing and other symptoms.

With some clinical tests, your medical team can help determine if your neck is involved in your particular injury.

Vestibular Injuries

Your vestibular system is important for balance and movement.  If things go wrong in this system it can cause dizziness and vertigo or other difficulties (we’ll cover symptoms in Part 4).  The vestibular system is built of parts of your inner ear, brain and nervous system.  In some cases a concussion can lead to injury of these areas or affect how well they’re working.  A type of vestibular injury called Benign Paroxysmal Positional Vertigo (BPPV) can also happen with head impacts.  

Click for a larger version

 

Are my nerves injured too?

In rare cases, nerves in your head and neck can be injured during a concussion.   There are a dozen sets of nerves (or 13, depending if you count the terminal nerve) that come from your brain and brain stem called the cranial nerves.  These nerves are involved in important things like smell, sight, sensation, taste, hearing, balance, speaking and swallowing.

  • Blurred vision, double vision and dizziness might be caused by cranial nerve injury

  • Sometimes people experience changes in smell and taste as well if these nerves are injured.

  • Facial and scalp pain and numbness might also happen if some of these nerves are injured or irritated.  

  • Hearing can also be affected

  • If you notice any symptoms like this, it’s important to see a doctor for assessment to see if cranial nerves are involved.  Your PT should also screen cranial nerves to make sure they’re working well.

Click the image to see the 12 cranial nerves.

 

Endocrine issues

We discussed the endocrine system in a previous post.  This system makes hormones and controls important body functions. There are 3 main endocrine glands in the brain: the pituitary gland, pineal gland  and hypothalamus.  Because of it’s shape and location in the brain, the pituitary is more prone to injury in concussion.  Although it’s more common in moderate or severe injury, endocrine issues can happen in concussion too.

 

Activity and thinking changes

The amount of physical and cognitive activity we do, and the thoughts we have all affect our brains on the chemical and connection level.  This is true for a uninjured brain and one after concussion.  The actions we take after injury can influence the biochemistry of the brain including how energy is used, how connections are made and the balance of neurotransmitters.


Conclusions:

  • Concussion is not a simple injury.  There’s more going on than just a bump to the brain
  • Brain function, connectivity and activity change after concussion; brain cells get injured, and almost any body system can affected in some way (including the vestibular/balance, endocrine, circulatory and nervous systems).  
  • Most of these issues are temporary and will run their course within a few weeks.  But there are some things you can do to speed up recovery or get better even if progress is slow.  
  • It’s important to seek out an experienced team who can help you with each of the issues related to concussion.  No single medical practitioner is able to treat all concussion issues alone.

 

At Tall Tree, we work hard to help people better understand their injury and get all of the help they need.  We’re happy to answer any question you have, or point you towards someone else who can answer it better. Get in touch anytime.

 

REFERENCES:

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