basal ganglia - jullet Flashcards
Where is the basal ganglia found?
deep, subcortical white matter of the forebrain, diencephalon, midbrain
The basal ganglia consists of:
1) Striatum, 2) Globus Pallidus, 3) Subthalamic nucleus, and 4) Substantia Nigra
What does the striatum consist of?
caudate nucleus, putamen, and nucleus accumbens
What does the globus pallidus consist of?
interna and externa
What is the lentiform nucleus?
region of the brain that consists of 1) putamen, 2) globus pallidus interna, 3) globus pallidus externa
What does the substantia nigra consist of?
pars reticulate and pars compacta
What is the main input to the striatum? (2)
1) excitatory glutamatergic input from the cortex + 2) dopaminergic input from the substantia nigra pars compacta; can be excitatory or inhibitory
What is the main output of the striatum?
GABAergic output to the basal ganglia (globus pallidus interna OR externa)
What is the main input to the basal ganglia (GPi)?
GABAergic input from the striatum
What is the main output of the basal ganglia (GPi)?
GABAergic output to the VA/VL thalamic relay neurons (tonic inhibition)
What is the main input to the thalamic relay neurons?
GABAergic output from the basal ganglia (GPi)
What is the main output of the thalamic relay neurons?
frontal motor cortical neurons
What is the main input to the frontal motor cortical neurons?
thalamic relay neurons
The medium spiny neurons respond to dopamine and glutamate in different areas of the cell. What are these parts and what is the functional significance of this? What is the net effect of the MSNs?
SHAFT: dopamine. SPINES: glutamate. PURPOSE: excitatory input into the striatum is modulated by substantia nigral dopaminergic input. NET: MSNs integrates these inputs and sends GABAergic signals to the globus pallidus interna/basal ganglia
What is the function of the cerebellum?
fine tune movement by integrating and coordinating sensory with motor function
What is the function of the basal ganglia?
integrate widespread cortical input and select the desired program for movement while suppressing unwanted/competing programs
What is the functional output of the basal ganglia?
tonic inhibition of thalamic relay neurons
What is the purpose of the motor loop in the brain?
it’s responsible for two modulatory functions: 1) scaling motor patterns in the context of task requirements, 2) controlling the assembly of overall motor plans
What does extrapyramidal mean?
non-cortical portions of the motor system (ie basal ganglia
What is the main neuronal cell type of the striatum?
medium spiny neurons
What is the function of the substantia nigra pars reticulata (SNpr)?
receives striatal afferents (mostly from caudate nucleus) and project tonically active GABAergic efferents to the superior colliculus
What is the nucleus accumbens?
rostral-most portion of the striatum and is contiguous with the caudate and putamen; regulates behavior and cognition (rather than movement and posture)
What is the VA/VL nucleus of the thalamus?
thalamic relay nucleus with excitatory (glutamatergic) projections to the frontal cortex
What is the direct pathway?
projection pathway that involves the cortex, caudate/putamen, globus pallidus INTERNA, VA/VL thalamic relay nuclei, and back to motor/frontal cortex.
What does activation of the direct pathway result in?
movement
What is the indirect pathway?
projection pathway that involves the cortex, caudate/putamen, globus pallidus EXTERNA, SUBTHALAMIC NUCLEUS, VA/VL thalamic relay nuclei, and back to motor/frontal cortex.
What does activation of the INdirect pathway result in?
inhibits movement by attenuating the direct pathway
What is the ventral striatal system?
functionally distinct part of the basal ganglia that has a role in regulating behavior and cognition (rather than movement and posture - caudate/putamen); aka NUCLEUS ACCUMBENS
What is the dorsomedial thalamus?
portion of the thalamus connected with the ventral striatal system (nucleus accumbens) that is associated with limbic function
What is the ventral tegmental area (VTA)?
dopaminergic neurons of the ventral striatal system that lies medially to the substantia nigra and provides dopaminergic tone to the nucleus accumbens
What happens to the direct pathway at REST?
No cortical input to the caudate putamen»_space; no inhibition of GPi»_space; GPi tonically inhibits the thalamic relay nucleus»_space; prevents inappropriate activation of motor programs
What happens to the direct pathway DURING MOVEMENT?
Cortical input to caudate/putamen»_space; caudate/putamen inhibits globus pallidus interna»_space; thalamic relay nucleus is not inhibited and increases activation of the motor/frontal cortex»_space; movement
What happens to the substantia nigra pars DURING MOVEMENT?
substantia nigra releases dopamine»_space; enhances the glutamatergic activation of the striatum (caudate/putamen); net effect: movement
What happens to the indirect pathway at REST?
No cortical input to the caudate putamen»_space; no inhibition of GPe»_space; GPe increases tonic inhibition of subthalamic nucleus»_space; Globus pallidus interna is not activated»_space; decreased tonic inhibition of thalamic relay nucleus»_space; increased activity of the motor/frontal cortex»_space; movement
What happens to the indirect pathway DURING MOVEMENT?
Cortical input to the caudate putamen»_space; globus pallidus externa is inhibited»_space; subthalamic nucleus activity increases»_space; globus pallidus interna is activated, which increases its inhibition on the thalamic relay nuclei»_space; no movement
Why is it that dopamine have different effects on the direct and indirect pathways?
DIRECT: has D1 receptors, which respond (+) to dopamine, resulting in enhanced glutamatergic transmission. INDIRECT: has D2 receptors, which respond (-) to dopamine, resulting in decreased glutamatergic transmission
What type of dopamine receptors dominate in the direct pathway? What is the effect?
has D1 receptors, which respond (+) to dopamine, resulting in ENHANCED glutamatergic transmission
What type of dopamine receptors dominate in the indirect pathway? What is the effect?
has D2 receptors, which respond (-) to dopamine, resulting in DECREASED glutamatergic transmission
What is the net effect of dopamine on both the indirect and direct pathways?
promotes movement
What areas of the body are served by the globus pallidus interna?
trunk/limbs
What areas of the body are served by the substantia nigra pars reticulate?
head/eyes
What are some charcteristics the direct pathway? What is the functional significance of this?
projections are more FOCUSED and have SMALLER representative field. Functional significance: recruits a set of desired motor programs when activated
What are some charcteristics the indirect pathway? What is the functional significance of this?
projections are more BROAD and have LARGER representative field. Functional significance: refines suprressing/unwanted competing motor programs
The striatum is further organized into two distinct compartments based on the presence or absence of AChE. What are these two compartments?
Striosome (lacks AChE) and Matrix (has AChE)
What is the striasome of the striatum?
lacks AChE. INPUT: pre-frontal cortex. OUTPUT: GABAergic output to SNPc to modulate dopaminergic input.
What happens if you lose the the striasome?
X-linked dystonia parkinsonism of Lubag
What causes X-linked dystonia parkinsonism of Lubag?
loss of striasome of striatum
What is the matrix of the striatum?
contains AChE; contains direct/indirect pathway
What type of disease is Parkinson’s?
HYPOkinetic disease
What degenerates in Parkinson’s disease?
dopaminergic neurons of substantia nigra pars COMPACTA
What is the net effect of Parkinson’s disease?
failure/inability to initiate movement
How does Parkinson’s disease work?
degeneration of dopaminergic neurons of substantia nigra pars compacta»_space; reduced activity of direct pathway»_space; increased activity of indirect pathway»_space; excess tonic inhibition of thalamus»_space; insufficient frontal/motor cortex excitation»_space; failure to initiate movement
What type of disease is Huntington’s?
HYPERkinetic disease
What degenerates in Huntington’s disease?
loss of medium spiny neurons of INDIRECT pathway of caudate/putamen
What is the net effect of Huntington’s disease?
excess/unintentional movements
How does Huntington’s disease work?
loss of medium spiny neurons of INDIRECT pathway of caudate/putamen»_space; globus pallidus externa increases tonic inhibition of subthalamic nucleus»_space; decreased tonic inhibition of thalamic relay nuclei»_space; increased activity of frontal cortex»_space; excess movements
What is choreoathetosis? What is it caused by?
exess/unintentional movements – caused by loss of medium spiny neurons of INDIRECT pathway of caudate/putamen (Huntington’s disease)
What are the non-motor functions of the basal ganglia?
executive functioning of the pre-frontal cortex, emotion/memory of the limbic system, speech, etc
What part of the striatum is involved in non-motor functions?
nucleus accumbens
What happens if there are lesions to the INdirect pathway components?
Lose attenuating effect of the indirect pathway (ie get unopposed direct pathway activity, which promotes movement). Results in BALLISTIC movements of contralateral limb
What happens if there is a lesion in the nucleus accumbens part that regulates speech?
nucleus accumbens is involved in non-motor functionsl; therefore lesion in the regions that control speech will result in inappropriate utterances/vocalizations/tics
What happens if there is a lesion in the nucleus accumbens, in particular the limbic/prefontal loops?
hallucinations, delusions, impaired cognition, lsos of emotional expression
