Neural plasticity in Neurological conditions Flashcards
What are the 2 different stages of recovery in neural plasticity?
And how do they differ?
- Direct or restorative mechanisms (Spontaneous recovery); initiated by the brain and is an attempt to bring about reactivation of damaged neurons.
- Forced recovery; Due to an intervention being applied, compensation, learning new ways to do old things.
There are 3 stages of spontaneous recovery, what is stage 1?
Using stroke as an example describe the fist stage.
Reduction of cerebral oedema:
Firstly;
- It is space occupying situation which occupies space in the brain, and given the fact that the capacity in the cranium is reduced, so the increase in cerebral oedema that occurs after damage, will result in compression of the neurons in the brain, and that will give rise to the typical stroke symptoms.
Then;
- After a while the brain will compensate for this and reduce the oedema thus reducing the pressure on the neurons,
leading to the survival of those neurons. This is one process that may then give rise to reactivation of these neurons, leading to spontaneous recovery.
There are 3 stages of spontaneous recovery, what is stage 2?
Using stroke as an example describe the second stage.
Reperfusion of ischaemic penumbra;
In stroke there is a disruption of blood flow, and all the neurons in the region will have a reduction in their neural function, if the reduction in blood flow goes below a critical level, neurones will begin to die. the longer the disruption the more neurons will die. They will be made up of neurons particularly close to the centre of that ischemic region, known as the ISHEMIC CORE. There you will have neurons which are irreversibly damaged and nothing you do will bring them back.
However surrounding the ischemic core there are another ring of neurons known as the ISHEMIC PENUMBRA, for these they did have a reduction in blood flow but the neural activity was depressed not totally lost.
This is because they didn’t loose their structural integrity, this means that subsequent reactivation of blood flow can re activate them and cause their survival. The longer the disruption of blood flow then the ischemic penumbra will join the ischemic core and be irreversibly damaged.
This small time window allows physicians to recover these neurons via therapeutic interventions, such as thrombolysis which opens up the blood channels again, to reperfusion these neurons the more of these neurons you’ll save.
There are 3 stages of spontaneous recovery, what is stage 3?
Using stroke as an example describe the third stage.
Reversal of Diaschisis;
- Disruption in blood flow and reduction of metabolism that is seen in otherwise intact regions of the brain that are anatomically linked or connected to the injured zone.
- E.g. You have the motor cortex being injured by stroke, and because the motor context is linked to the other hemisphere you have the other hemisphere undergoing some reduction in blood flow or some reduction in metabolism. Or the corticospinal tract that is connected to the motor cortex undergoing some sort of reduced perfusion or reduced functioning, bc of the injury to the motor cortex. The reason for this is the reduced excitatory input coming from the damaged region of the remote areas/centres.
Studies believe that spontaneous recovery can be due to the reversal of Diaschisis. But conflicting evidence has shown that diaschisis doesn’t show any correlation of recovery after stroke. But generally it is believed that this does contribute to spontaneous recovery..
Between which months does the most recovery of motor patterns post stroke, take place?
In the first 3 months,
(particularly 0-1month)
After 3 months recovery slows down and little change post 6 months.
What is compensation?
Neural tissue acquires a function it did not have pre-injury, e.g. neural plasticity.
So e.g. performing an old movement in a new manor. like opening a bag of crisps with a hand and mouth oppose to using both hands.
What is recovery?
Restoring function in neural tissue that was initially lost after injury.
May be seen as reactivation in brain areas previously inactivated by the circulatory event, although this isn’t expected to occur in the area if the primary brain lesion, but may occur in surrounding areas (penumbra) and in diaschisis.
E.g. being able to perform a movement in the same manor as pre-injury.
What factors might explain the differences in recovery patterns seen in neurological patients?
- Age
- Lesion factors
- Genetic factors
- Weight (more about physical inactivity)
- Gender
- Brain trophic
- pre-morbid factors e.g. level of activity, diet pre-injury etc
- Severity of stroke
What is Neural plasticity?
Plasticity is the ability for the brain to reorganise itself, can involve short/long term remodelling of the organisation of its neuronal networks in response to experiences of the body/ injury.
What can trigger neuroplastic changes?
- PNS damage
- CNS damage
- Motor learning/skill learning
- Environmental experiences.
Inter-cellular responses to damage.
What is denervation hypersensitivity and what occurs?
- Denervation hypersensitivity;
This occurs in Parkinson’s disease, neurons become hypersensitive to neurotransmitters, as less of the neurotransmitter becomes available due to the destruction of the striatal pathways, eventually the post synaptic membrane develop more receptor sites and become more sensitive to the neurotransmitter, so you can have continual stimulation of these pathways.
Inter-cellular responses to damage.
What is Unmasking of silent synapses and what occurs?
With damage to particular neurons, silent synapses close to these are ‘unmasked’ and they become activated and sprout then take over the role of the damaged/lost neurone.
Inter-cellular responses to damage.
What is Regenerative synapse agenesis and what occurs?
This occurs when neurons die, and their stump regenerates to connect with the post synaptic membrane that remaining, continuing the activation of that pathway.
Inter-cellular responses to damage.
What is collateral sprouting and what occurs?
When the pathways that are close to the ones that have dies generate stumps and sprout across, and connect to the pathways that were damaged.
Inter-cellular responses to damage.
What is neural regeneration and what occurs?
When new neurons are birthed after the death of others. These grow and take over the pathways of the dead ones.
