Sievert: Basal Ganglia Flashcards
What is the basic loop from the basal ganglia to the cortex?
basal ganglia –> thalamus –> cortex –> basal ganglia
Do to the basal ganglia project to the same side or the opposite side?
always project to the contra side
Where is the subthalamic nucleus located?
underneath the thalamus, rostral to the substantia nigra
Where is the substantia nigra located?
in the midbrain, above the cerebral peduncles
The striatum is considered the (blank) zone. What are its two components?
receiving; caudate and putamen
What makes up the lenticular nucleus?
putamen and globus pallidus
The efferent zone of the basal ganglia that consists of the globus pallidus and the substantia nigra
pallidum
What are two additional nuclei that are functionally part of the basal ganglia?
substantia nigra
subthalamic nucleus
What constitutes the receiving zone of the basal ganglia?
caudate and putamen
How are the caudate and putamen similar and how are they different?
they are functionally similar in terms of their efferents, but slightly different in terms of their afferents
In general, the striatum receives input from what areas?
all areas of the cortex except for the primary visual and primary auditory areas
**also gets an important input from the substantia nigra
What makes the caudate a good receiving center?
It follows the lateral ventricle, so it is in a good position to receive inputs from almost all areas of cortex
What is the end result of the direct pathway?
increases excitatory thalamic input to the cortex, and turns UP motor activity
In the direct pathway, what happens from cortex to striatum? From striatum to GP? From GP to VA/VL? From thalamus to cortex?
excites striatum more inhibition to GP less inhibition to Va/Vl Va/Vl more active more excitation to motor cortex
What is the end result of the indirect pathway?
decreases excitatory thalamic input, so turns DOWN motor cortex activity
In the indirect pathway, what is the effect from cortex to striatum? What is the effect from striatum to external GP? What is the effect from external GP to subthalamic nuclei? What is the effect fromr subthalamic nuclei to internal GP? What is the effect from internal GP to Va/Vl? What is the effect from Va/Vl to motor cortex?
excitation; inhibitory; inhibitory to subthalamic nuclei; excitatory to GPi; inhibitory to Va/Vl; less output from Va/Vl = less motor cortex firing
What is the effect of the substantia nigra on the direct pathway (D1)? What about its effect on the indirect pathway? What is the net result of both pathways?
turns UP the direct pathway
turns DOWN the indirect pathway
increased VA/VL drive to cortex and more motor activity
The striatum has small (blank) which act on the two paths (direct and indirect)
cholinergic cells
What effect do cholinergic cells have on the direct pathway? On the indirect pathway? What is the overall effect of these cells?
turn DOWN the direct pathway; turn UP the indirect pathway; decrease VA/VL drive to cortex = less motor activity
What are the two categories of basal ganglia disorders?
hypokinetic
hyperkinetic
Is Parkinson’s disease hypo or hyperkinetic? What are some symptoms?!
hypokinetic; tremor at rest masked facies rigidity retropulsion festinating gait shuffling gait loss of postural reflexes depression, anxiety, dementia
Parkinson’s is a disorder due to a loss of the dopamine projecting cells from the (blank) to the (blank). The loss on the direct path is to reduce excitation of the striatum which causes a decrease in motor activity. Essentially the small ACh cells become dominant.
nigra; striatum
If there is less dopamine (as seen in Parkinson’s), what affect does this have on the direct pathway?
reduced excitation of the striatum, which causes a decrease in motor activity (so decreased activity of the direct pathway)
The balance between ACh and Dopamine is important. If you lose dopamine (as seen in Parkinson’s), what will happen to ACh?
the ACh cells will become dominant and will result in less motor activity
What is the result of Parkinson’s on the indirect pathway?
Increases the indirect pathway!! lose dopamine cells affecting D2 receptors less inhibition of the indirect pathway reduced motor output of the Va/Vl nuclei small ACh cells are dominating
What are two examples of hyperkinetic syndromes?
Huntington’s Chorea
Hemiballismus
What is hemiballismus caused by? What is a characteristic feature of hemiballismus?
damage to the subthalamic nucleus; wild flinging movements of the body
What does hemiballism do to the indirect and direct pathways? What does it ultimately result in?
takes out the entire indirect pathway and lets the direct pathway dominate; results in increase in motor outputs
When does Huntington’s chorea usually express? What does it result in?
in the 4th and 5th decade;
results in movement disorder followed by dementia and death
What symptoms of Huntington’s disease are the first to manifest?
rapid, jerky dance-like movements in the extremities
What is the initial insult in Huntington’s disease? What does it ultimately lead to?
loss of striatal cells projecting to the indirect path
**later complicated by a secondary loss of the small Ach cells of the striatum;
increase in activity of motor thalamus
When you consider Basal Ganglia disorders, it is useful to think about the hypo and hyperkinetic syndromes as being an imbalance between the (blank) and the (blank) in the striatum.
dopamine; ACh
How can Parkinson’s be treated?
increasing the level of dopamine
How can Huntington’s be “treated?”
elevate the ACh levels in the striatum
What are other solutions to disorders of the basal ganglia?
give L-dopa as a precursor to dopamine
transplant dopamine producing cells
give stem cells
deep brain stimulation
What do lower motor neuron syndromes cause? What kind of deficit do they produce in the spinal cord?
paralysis
muscle atrophy
areflexia and atonia;
ipsilateral deficit
What do upper motor neuron syndromes cause?
What kind of deficit do they produce in the spinal cord?
paresis (weakness)
no atrophy
hyperflexia, hypertonia, spasticity
contralateral deficit above the decussation and ipsilateral deficit below the decussation
Do basal ganglia disorders cause paralysis? Atrophy? What kind of deficit do they produce in the spinal cord?
no; no; contralateral
What is the effect of Parkinsons disease on the direct pathway?
Decreases the direct pathway!! Loss of the dopamine projecting cells from the nigra to the striatum. The loss on the direct path is to reduce excitation of the striatum which causes a decrease in motor activity. Essentially the small ACh cells become dominant.
