Basal Nuclei Flashcards
What are the basal nuclei?
Also called cerebral nuclei
A collection of nuclei deep to the white matter of the cerebral cortex
Masses of gray matter that direct subconscious activities
What are the components of the basal nuclei?
Caudate nucleus
Putamen
Globus pallidus
Subthalamic nucleus
Substantia nigra
What do the basal nuclei do?
Reduce or dampen the excitatory input to cerebral cortex
Provide a postural platform off which purposeful movement can be made
Describe the output of the basal nuclei
(Thalamus point of view)
Most of the output in mediated by the thalamus
When discharge patterns of the basal nuclei are excessive there will be an abnormal slowing of movements
If there is reduced output involuntary movements occur at periods of rest
Describe the input to the striatum
Putamen - primary motor area, secondary motor area, primary somatosensory area
Caudate nucleus - association areas, frontal eye fields, limbic system
What activities do the basal nuclei encode for?
Decisions to move
Direction of movement
Amplitude of the movement
Motor expression of emotions
Describe the output from the basal nuclei
(GPi point of view)
From the globus pallidus interna (medial)
Via GABA-ergic neurons
To the thalamus
Thalamus under tonic inhibition
Overall output from the thalamus is excitatory to the cortex
Strength of thalamic signal dependent on GPi
Is there a specific organisation type in the basal nuclei?
Somatotopic organisation is maintained in the basal nuclei
What are the transmitters and transmission type of the components of the basal nuclei?
Caudate nucleus - GABA (Inhibitory)
Putamen - GABA (Inhibitory)
Globus pallidus interna (medial) & externa (lateral) - GABA (Inhibitory)
Subthalamic nucleus - Glutamate (Excitatory)
Substantia nigra - Dopamine (Excitatory or inhibitory)
What are GPi/SNr?
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Are the major output nuclei
Output is inhibitory
These neurons have high baseline firing rates in
Briefly state the direct pathway of the basal nuclei
The wiring of this circuit releases the thalamus from its tonic inhibition leading to more excitation of the cortex and in turn more cortical output
Facilitates target orientated and efficient behaviour
Briefly describe the indirect pathway of the basal nuclei
This circuit wiring inhibits the output from the thalamus leading to less excitation of the cortex and in turn less cortical output
Suppresses superfluous behaviours that are not related to targeted behaviours
List the steps of direct pathway (1) of the basal nuclei
Neurons from the cortex release glutamate onto the Putamen
This stimulates neurons of the Putamen to release GABA onto the globus pallidus interna
GPi is inhibited - less GABA is released onto the ventrolateral nucleus
This then allow the VL to excite the cortex
List the steps of direct pathway (2) of the basal nuclei
Neurons from the cortex release glutamate on the Putamen (higher activity in the Putamen)
Heightened activity causes more release of GABA onto the substantia nigra
Less activity of the SNr
Less inhibition of the VL neurons
More activity in the cortex due to less inhibition of the VL
What is the influence of the substantia nigra (compacta) on the direct pathway?
Sends Dopaminergic connections to the Putamen that synapse into excitatory D1 receptors
(Similar to excitation of the cortex)
Excites the inhibitory connections from the Putamen to the globus pallidus interna and substantia nigra (reticula)
Releases VL from inhibition to allow cortex cortex excitation
List the steps of indirect pathway (1) of the basal nuclei
Glutamatergic excitatory input from the cortex to Putamen
Excitation of GABA-ergic inhibitory connections from Putamen to globus pallidus externa
(Less activity in GPe)
Less inhibition of GABA-ergic connections from GPe to subthalamic nucleus
Releases inhibition of glutamatergic connections between STN and GPi
(More activity in GPi)
Excitation of GABA-ergic input from GPi to VL
(more Inhibition of VL)
Less excitation of glutamatergic input to the cortex
Less activity in the cortex
List the steps of indirect pathway (2) of the basal nuclei
Glutamatergic input from cortex to Putamen
Excitation of GABA-ergic inhibitory connections from Putamen to GPe
(Less activity in GPe)
Less inhibition of GABA-ergic connections from GPe to STN
(More activity in STN)
Releases inhibition of glutamatergic excitatory input from STN to SNr
(More activity in SNr)
Excitation of inhibitory GABA-ergic input from SNr to VL
(Less activity in VL)
Less excitation of glutamatergic input to cortex
Less activity in the cortex
What is the influence of the SNc on the indirect pathway?
Releases dopamine onto D2 inhibitory synapses
Under normal conditions produces less inhibition into the GPe
D2 inhibits the indirect pathway
What happens in Parkinson’s disease?
Decreased output of SNc Dopaminergic projections
Decreased inhibition in direct pathway
Increases excitation in indirect pathway
Net effect - more inhibition of the thalamus and therefore less excitatory input to motor cortex
Describe the effects on Parkinson’s on the direct pathway
Less excitation from SNc to Putamen
Less inhibition of GPi and SNr
More tonic inhibition of VL
Less excitation of cortex
Describe the effects Parkinson’s has on the indirect pathway
Less dopamine released on inhibitory D2 receptors
More inhibition from Putamen to GPe
Less inhibition from GPe to STN
More excitation from STN to GPi and SNr
More inhibition from GPi and SNr to VL
Less excitation of the cortex
What happens in Huntington’s disease?
Cell loss in the striatum that seems to affect the direct pathway disproportionately
Less inhibition of the thalamus and therefore excessive excitation of motor cortex
