neurological causes of parkinsons Flashcards
(12 cards)
What is the area in the brain which is linked to parkinsons disease?
The substantia nigra is part of the basil ganglia- a midbrain structure, specifically a dopaminergic nucleus.
This area of the brain plays a crucial role in motor control and reward functions as part of the basal ganglia circuit.
The main role of the basil gangglia is to inhibit unwanted motor activities.
how does the loss of dopamine in this area lead to parkinsons?
As dopamine neurons are lost in the substantia nigra, PD patients find it hard to initiate voluntary movements.
low levels of dopamine= harder to initiate voluntary movements.
what causes death of dopamine neurons?
events leading to dopamine cell death are widely misunderstood.
the presence of lewy-bodies (alpha-synuclein) are currently the subject of intensive research.
Lewy bodies reflect a key pathological process that damages the neurons responsible for dopamine production.
what are lewy bodies?
Lewy bodies are abnormal aggregates of a protein called ‘A-SYNUCLEIN’- along with other proteins, that accumulate inside neurons.
they are a hallmark of parkinson’s disease pathology, especially in teh substantia nigra.
where do lewy bodies accumulate?
they form dopaminergic neurons in the substantia nigra pars compacta.
as these neurons degenerate and die, dopamine levels in the striatum drop- leading to motor symptoms like tremor, rigidity and bradykinesia.
How do lewy bodies contribute to dopamine loss?
the build up of misfolded a-synuclein in Lewy bodies:
disrupts normal cell function
triggers cellular stress and inflammation
eventually leads to neuronal death.
since the affected neurons are the main source of dopamine in the brain, their death leads directly to the dopamine deficiency seen in parkinsons.
explain lewy-body progression
Lewy body pathology can spread through the brain overtime- braak stages.
starts in the lower brainstem and olfactory regions and eventually reaches the cortex
this explains the non-motor symptoms of PD such as cognitive decline that may develop later.
what happens in the caudate nucleus once dopamine neurons in the sustantia nigra die?
once dopamine neurons in the SN die, there is a loss of dopamine.
since the caudate nucleus recieves dopamine from the SN, the loss of this leads to reduced stimulation of the ‘direct pathway’ and less inhibition of the ‘indirect pathway’
leads to increased inhibition of motor signals due to the balance of these pathways being disrupted.
how does this lead to overactivity in the Globus Pallidus Internus?
Due to the dopamine loss, the globus pallidus internus becomes over active.
The GPi sends inhibitory signals to the thamalus
overactivity means more inhibition is sent to the thalamus than normal.
explain this impact on the motor cortext
the thalamus normally activates the motor cortex to initiate movement.
however in PD, its being over-inhibited by the GPi, so it under-stimulates the motor cotex.
results in= slower or reduced movement (bradykinesia)
what brain areas are a part of intricate feedback loops?
the basal ganglia, thalaus and motor cortex and part of intricate feedback loops that fine-tune movement.
disruption of these loops due to dopamine loss leads to the classic motor symptoms of PD.
leading to gradual onset of symptoms over time.
summary of this
dopamine loss=
less movement-promoting signals in the basal ganglia=
increased inhibition of thalamus=
reduced activation of motor cortex=
motor symptoms of PD.
