TASK 2 - BASAL GANGLIA Flashcards Preview

Functional Neuroanatomy > TASK 2 - BASAL GANGLIA > Flashcards

Flashcards in TASK 2 - BASAL GANGLIA Deck (27):

basal ganglia

= large set of nuclei
- caudate, putamen, globus pallidus: motor components
- telencephalon, diencephalon (sub thalamic nuclei), mesencephalon (substantiva nigra)
- links most of the cerebral cortex with upper motor neurones in M1, premotor cortex and in the brainstem


role of basal ganglia in movement

- (+ cerebellum) influence movement by regulating activity of upper motor neurons --> no direct projection to local circuit or lower motor neurones
- facilitate movement initiation
- facilitate suppression of competing motor programs that would otherwise interfere with expression of goal-directed behaviour
- modulation of activity in anticipation of and during movements (smooth movements)


input nuclei

- cortex = largest input to basal ganglia; only primary visual + auditory cortex have no projections to the striatum
1. striatum: almost all input; from much of cerebral cortex (mostly from frontal and parietal lobes, followed by temporal, insular and cingulate cortices)
--> corticospinal pathway = multiple pathways serving different functions
a. caudate
b. putamen
2. substantia nigra pars compacta


input nuclei
1. striatum

- input zone, destinations of most pathways + incoming axons from the cerebral cortex and other parts of the brain
- medium spinal neurones = large dendritic trees that can integrate various inputs
- GABAergic neurones
- functionally subdivided to its inputs --> reflects specialisation of cortical areas that provide input


1a. caudate

- input from association cortices + motor areas in frontal lobe that control eye movements (FEF)
- occumolotor loop
- anticipatory discharge of eye movements


1b. putamen

- input from primary, secondary somatic sensory cortices in parietal lobe + secondary (extrastriate) visual cortices in occipital and temporal lobes + premotor and motor cortices in frontal lobe + auditory association areas in the temporal lobe
- motor loop
- anticipatory discharge of limb and trunk movements
- activity in these cells encode decision to move toward a goal


input nuclei
2a. substantia nigra pars compacta

- input: main dopaminergic aminergic inputs originate
- inputs relatively far from the initial segment of the medium spiny neurone axon
- neurones exhibit very little spontaneous activity and must simultaneously receive many excitatory inputs from cortical and nigral neurones to overcome stabilising influence of this potassium conductance (which remains a stable resting membrane potential, close to depolarisation)


output nuclei

- major pathways that allow basal ganglia to influence activity of upper motor neurones located in motor cortex and brainstem; 2 pathways
- GABAergic neurones/output = high levels
- activity prevents unwanted movements by tonically inhibiting cells in thalamus and superior colliculus
1. pallidum: main sources of output
a. globus pallidus: large number of myelinated axons (pale)
b. substantia nigra pars reticular: reticular/netlike form


3. globus pallidus

- pathway to cortex
1. globus pallidus internal (GPi)
2. relays in ventral anterior + ventral lateral nuclei of dorsal thalamus
3. project directly to motor areas (M1, SMA, PFC)
- motor loop: multiple areas of cortex --> processing in basal ganglia and thalamus --> terminating in motor areas


2b. substantia nigra pars reticulata

- control head and eye movements
1. substantia nigra pars reticulata (SNr)
2. project to + terminate in superior colliculus (initiation of eye movement)
- more direct: without intervening relay in thalamus
- many also project to thalamus to relay info to frontal eye fields and premotor cortex


4. subthalamic nuclei

- ventral thalamus
- diencephalon


direct pathway

1. activation of medium spiny neurones in input nuclei (= striatum)
2. inhibition of GPi
3. disinhibition of ventral thalamus
4. activation of frontal cortex


direct pathway
- dopamine pathway

- substantia nigra (SNc) excites direct pathway via acting on D1 receptor --> striatum excited = inhibits GBi MORE
- ENHANCES EFFECT = more wanted movement (centre action is strongly supported)


indirect pathway

1. activation of striatum
2. inhibition of GPe
3. disinhibition of STN
4. MORE activation of GPi
5. MORE inhibition of thalamus
6. NO activation of frontal cortex


indirect pathway
- dopamine pathway

- substantia nigra (SNc) inhibits indirect pathway via acting on different type of D2 receptor (D2) --> striatum inhibited = inhibits GPe LESS
- REDUCES EFFECT = more unwanted movement (surrounding actions more uncontrolled)


centre-surround functional organisation

- direct pathway = centre = activation of intended motor programs
--> facilitation of voluntary movements
- indirect pathway = surround = suppression of competing motor programs
--> suppression of inappropriate movements


dopamine pathway

- internal pathway
- role: contribute to reward-related modulation of behaviour
- EXCITES direct pathway
- INHIBITS indirect pathway


basal ganglia disorders
- Parkinson's disease

= hypokinetic movement disorder
= failure of disinhibition
- causes: loss of nigrostriatal dopaminergic neurones
- results in abnormally high inhibitory output of the basal ganglia --> lesser thalamic activation of upper motor neurones
- motor symptoms: resting tremor, slowness of movement (= bradykinesia); diminished facial expressions, lack associated movements (= akinesia) --> failure of normal disinhibition
- cognitive symptoms: lack of cognitive drive/motivation, decision making deficits; sometimes associated with dementia
- any movement is difficult to initiate + once initiated often difficult to terminate
- not able to act on internal cues BUT on external cues


Parkinson's disease
- pathways

dopamine pathways degenerated:
1. less facilitation of direct pathway = less activation of voluntary movements
- increases responsiveness of direct pathway to corticospinal input
- more inhibition of thalamus
2. less reduction = suppression of inappropriate movements
- decreases responsiveness of indirect pathway to input
- more inhibition of thalamus
--> MORE INHIBITION = less movement initiation; cortex almost impossible to activate


Parkinson's disease
- treatment

- l-DOPA
- stem cells, gene therapy
- deep brain stimulation: GPe, STN, GPi


basal ganglia diseases
- Huntington's disease

= hyperkinetic movement disorder
= failure of Inhibition
- causes: degeneration of medium spiny neurons (striatum) that project to the globus pallidus (GBe) --> atrophy of caudate and putamen (striatum)
- results in abnormal activation of GPe --> reduces excitatory output of STN to GPi + inhibitory outflow of basal ganglia --> without restraining influence upper motor neurones can be activated by inappropriate signals
- symptoms: involuntary movements; alteration in mood/change in personality (increased irritability…); defects of memory and attention; rapid, jerky motions with no clear purpose (= choreiform movements)


Huntington's disease
- pathways

medium spiny neurones degenerated = GBe degenerated:
1. more inhibition of direct pathway on GPe = more activation of voluntary movements
- more activation of thalamus
2. less activation of indirect pathway on GPe = less suppression of involuntary movements
- more activation of thalamus
--> MORE ACTIVATION = less control of movements; cortex easily activated


Huntington's disease
- treatment

- deep brain stimulation
- gene therapy: antisense treatment


cortico-striatal-thalamic loops
1. motor loop

= action, movement
1. motor areas (SMA)
2. putamen
3. lateral GPi
4. ventral lateral + ventral anterior thalamic nuclei


cortico-striatal-thalamic loops
2. occumolotor loop

- eyes
1. frontal eye field (FEF), PPC, PFC
2. caudate
3. GPi, SNr
4. mediodorsal + ventral anterior thalamic nuclei


cortico-striatal-thalamic loops
3. cognitive loop

- cognition
2. anterior/dorsolateral caudate (literature vs. lecture BUT caudate)
3. GPi, SNr
4. mediodorsal + ventral anterior thalamic nuclei


cortico-striatal-thalamic loops
4. limbic loop

- motivation/emotion
1. limbic system (anterior cingulate: emotion; orbitofrontal cortex: motivation)
2. ventral striatum: emotion (ventromedial caudate: motivation)
3. ventral pallidum
4. mediodorsal thalamic nuclei