Basal ganglia Flashcards
What are the two key roles of the basal ganglia?
- Initiation of voluntary movements
- Suppression of unwanted movements
What are the two structures of striatum?
- Caudate
- Putamen
What are the two structures of the pallidum?
- Globus pallidus
- Substantia nigra pars reticulata
Does the basal ganglia have a direct pathway to spinal cord?
No.
From which structures is the basal ganglia receiving its inputs? To which structures is basal ganglia sending its outputs?
- Receive from cortical structures.
- Send back computations to cortical structures.
What is the input zone of the basal ganglia? What kind of neuron is found there? What is the type of its neurons activity?
- Striatum (caudate and putamen)
- Medium spiny neurons
- Phasic activity (voluntary activation)
Where do converge most medium spiny neuron axons?
Pallidum structures.
Give the specific input and output pathways of the striatum structures.
Caudate:
- Input = receive connections from frontal lobe motor areas that control eye movements
- Output = projections to substantia nigra pars reticulata -> superior colliculus (responsible for saccades and head and neck orientation)
Putamen:
- Input = receive connections from SI and SII from parietal lobe, extrastriate visual cortices, premotor and motor cortices, auditory associate cortices
- Output = projections to globus pallidus -> thalamus ->motor and premotor cortex
What is the type of output from MSNs of putamen and caudate to globus pallidus and substantia nigra pars reticulata?
Inhibitory through inhibitory GABAergic projections.
What is the consequence of neurons of globus pallidus and substantia nigra pars reticulata having an spontaneous discharge (inhibitory tonic activity) (against MSNs that are only phasic)?
Inhibition of unwanted movement by inhibiting neurons in superior colliculus and thalamus.
MSNs receive inputs from many structures. Name 4.
- Cortical neurons
- Local circuit neurons
- Substantia nigra neurons (dopaminergic)
- Raphe nulcei
- Brainstem
True or false: MSNs receive thousands of inputs from a single cortical axon, but integrate the signals of only one cortical axon.
Faslse: receive few inputs from a single cortical axon, but integrate the signals of thousands of cortical axons.
Localize the inputs of the following structures on the MSNs:
- Cortical structures
- Local circuits
- Thalamic neurons
- Dopaminergic inputs from substantia nigra pars compacta
- Cortical structures ->on dendritic spines
- Local circuits ->on dendritic shafts and close to soma → modulate effects of cortical synapses
- Thalamic neurons ->on dendritic shafts and close to soma → modulate effects of cortical synapses
- Dopaminergic inputs from substantia nigra pars compacta ->on base of dendritic spines → modulate effects of cortical synapses
Why can we talk of gate-keeping in the neuronal circuitry of basal ganglia?
Neurons from pallidum structures are tonically inhibitory -> they prevent any unwanted movement to occur. They require to be inhibited to allow voluntary movements to be executed.
Consider the following basal ganglia circuitry:
A: medium spiny neuron from putamen
B: neuron from globus pallidus
C: neuron from VA/VL complex of thalamus
D: neuron from motor cortex
Assess the activity of each neuron when:
- A is at rest
- A is excited
A is at rest:
A: no activity
B: tonically inhibiting C
C: no activity
D: no activity
A is excited:
A: voluntary activity inhibiting C
B: Relieving inhibitory activity on C
C: transient activity
D: transient activity
What complex of the thalamus is implied in the initiation of movement by responding to inputs from basal ganglia?
VA/VL complex (ventral anterior nucleus and ventral lateral nucleus).
What are the main central pathways of basal ganglia? What are their respective main outcomes?
Direct pathway: release upper motorneurons from tonic inhibition to allow movement.
Indirect pathway: increase tonic level of inhibition to prevent any movement.
Describe activation of the direct pathway in basal ganglia.
Cerebral cortex activation (frontal lobe:primary motor cortex and premotor cortex) — + >caudate and putamen — - >globus pallidus, internal segment — less - > VA/VL complex of thalamus — + >frontal cortex.
Describe activation of the indirect pathway in basal ganglia.
Cerebral cortex activation — + > caudate and putamen — - > external segment of globus pallidus — less - > subthalamic nucleus — + > internal segment of globus pallidus — more - > VA/VL thalamus — - >frontal cortex.
True or false: activation of direct and indirect pathways will always make the pathways oppose to one another.
True.
True or false: indirect and direct pathways of basal ganglia are voluntary.
True.
Substantia nigra pars compacta can receive dopamine influxes at its D1 and D2 receptors. What are the consequences of such influxes on the direct and indirect pathways of basal ganglia?
- Dopamine influx at D1 receptors enhances activity of the direct pathway
- Dopmaine influx at D2 receptors suppresses activity of the indirect pathway
What is the overall net effect of dopamine influx at D1 and D2 receptors of substantia nigra pars compacta?
Decrease inhibitory outflow from BG (favouring the outcome of the direct pathway).
What is the theory of focus selection?
The hypothesis that direct and indirect pathways of basal ganglia are organized in a centre-surround fashion.
- The direct pathway in the centre mediates a focused activation of a functional unit
- The indirect pathway suppresses activity of surrounding functional units
What does support the centre-surround model of direct and indirect pathways organization?
The “focused selection” theory.
What does Parkinson’s disease cause on the level of basal ganglia structures?
Substantia nigra degenerates
Parkinson’s disease is associated with impairment of voluntray movements. How is that symptom called?
Dyskinesia.
Parkison’s disease results, amongst other symptoms, in difficulty to intiate and terminate voluntary movements. What is one possible cause?
Loss of dopamine in substantia nigra pars compacta.
What does Huntington’s disease cause on the level of basal ganglia structures?
Caudate and putamen shrinkage.
What syndrome concerning the neuropathology of basal ganglia produces ballistic and choreic movements?
Huntington’s disease.
What syndrome concerning the neuropathology of basal ganglia is associated with the dysfunctional gate-keeping function of the globus pallidus?
Huntington’s disease.
