Professor Dave here, let’s talk about neuroplasticity.
Because the brain is so important to our health, damage to the brain can cause severe impairment.
By studying brain damage, we can get a better understanding of how the brain works, and
also come up with ways to treat certain types of damage.
Let’s take a look at some causes of brain damage now.
The primary types of brain damage include tumors, cerebrovascular disorders, closed-head
injuries, brain infections, neurotoxins, and genetic factors.
Looking at tumors first, we discussed the basics surrounding cancer and tumor development
in the biochemistry series, so check out that tutorial if you need a refresher on what cancer is.
A common type of brain tumor is a meningioma, which is found between the meninges of the brain.
These are encapsulated, or contained within their own membrane, and therefore benign.
Meningiomas can be surgically removed, but other tumors are infiltrating, which means
that they are able to grow through surrounding tissue.
These tend to be malignant and difficult to remove.
The most common cerebrovascular disorder is commonly referred to as a stroke.
There are two types of strokes, a cerebral hemorrhage and a cerebral ischemia.
The first of these occurs when a blood vessel in the brain ruptures, allowing blood to seep
into neural tissue and damage it.
The second occurs when blood supply to a part of the brain is disrupted.
This can be due to a plug or a block in a small vessel, and this situation is called
thrombosis, or an embolism if the block is transported from a larger vessel.
This can also arise due to arteriosclerosis, where blood vessel walls become thicker and
channels narrow until blockage occurs.
When neurons are deprived of blood, they release excessive amounts of glutamate, which will
overactivate receptors in postsynaptic neurons.
This will cascade, and can also trigger events that kill neurons, which is a process called
excitotoxicity.
Closed-head injuries result largely from blunt force being applied to the head.
A hard hit can produce a contusion, which involves damage to the circulatory system
in the brain, resulting in internal hemorrhaging and a hematoma, which is essentially a bruise.
This is due to the brain forcibly impacting the skull.
Concussions are similar except that there is less long-term damage, but people who experience
frequent concussions like boxers and football players experience a cumulative effect that
eventually results in huge problems.
Pathogens can infect the brain just like any other part of the body, and the resulting
inflammation is called encephalitis.
These infections can be bacterial or viral.
If bacterial, they can lead to cerebral abscesses, which are pockets of pus, or meningitis, which
is a potentially fatal inflammation of the meninges.
If viral, the pathogen may have an affinity for neural tissue, such as with rabies, or
no particular affinity, such as with the mumps, but attack neural tissue all the same.
We will get a closer look at these and many others in the upcoming course on pathology
and infectious diseases.
Next with neurotoxins, these are toxic substances that enter general circulation from the GI
tract, lungs, or skin.
These include mercury or lead, which can accumulate in the brain and cause significant damage,
resulting in psychosis.
There can even be endogenous neurotoxins, meaning they originate in the body, in the
form of certain antibodies.
And lastly, damage can be of a genetic origin.
Certain recessive genes can be passed on that result in neurological or psychiatric disorders,
and other disorders can occur simply due to accidents during fertilization or embryonic
development.
Down syndrome is an example of such a disorder, where an extra copy of chromosome twenty-one
is produced in the egg, which causes a variety of complications.
Brain damage can result in a variety of neurological disorders ranging from epilepsy to Alzheimer’s,
and these will also be discussed at great length in the pathology course.
For now, let’s stick to brain function and examine some ways that the brain can respond
to brain damage in order to resume proper function.
These can be collectively referred to as neuroplasticity, which refers to the brain’s ability to reorganize
itself to form new neural connections so as to compensate for injury and disease.
Let’s go over four such responses now.
These will be degeneration, regeneration, reorganization, and recovery.
Beginning with neural degeneration, this is the deterioration and death of a neuron.
While this can be a symptom of disease, this can also be employed in normal brain development.
When an axon is severed, this is called axotomy.
As a result, there will be anterograde degeneration, which is deterioration of the remaining portion
that extends towards the synapse.
This is quite fast, as this section of the axon is now cut off from the cell body, so
metabolism is impossible.
There will also be retrograde deterioration, which involves deterioration in the other
direction towards the cell body, and this will take a bit longer, though it can be aided
by apoptosis.
Sometimes this effect can spread to adjacent neurons, and this is called transneuronal
degeneration.
Then there is the opposite process, neural regeneration.
This is tougher for mammals than for other animals, and almost never occurs in the central
nervous system, but it happens sometimes in the peripheral nervous system.
This is because axonal damage can occur without severing the Schwann cells, so some regeneration
can often result in the neurons regaining the ability to transmit information to their targets.
If Schwann cells are damaged, this becomes less and less feasible and axons can regenerate
to reach incorrect targets or no target at all.
By contrast, neural reorganization occurs when an axon is severed and a nearby neuron
exhibits collateral sprouting, allowing new axon terminals to synapse with the neuron
that the first neuron can no longer synapse with.
This strategy allows the brain to redirect traffic, so to speak, in the event of localized
brain damage.
Lastly, we can sometimes see complete recovery of function after damage to the central nervous
system, although this remains poorly understood.
Neuroplasticity is an exciting phenomenon, and current studies are helping us determine
ways to treat damage to the central nervous system in humans, as well as innovate treatments
for things like Parkinson’s disease.
We are examining possibilities surrounding neurotransplantation, and other such cutting
edge technologies that will help us treat spinal injury, phantom limbs, and other conditions.
But before we get to that, let’s dive into some cognitive functions so that we can get
a better understanding of human psychology from a biological standpoint.