Basal Ganglia Flashcards
1
Q
What is the basal ganglia
A
- This refers to a large and functional diverse set of neural structures buried deep within the cerebral hemispheres
2
Q
What are the neural structures of the basal ganglia
A
- Caudate
- Putamen
- Globus pallidus
3
Q
What do the caudate and putamen nuclei form together
A
corpus striatum
4
Q
What do the putamen and the globus pallidus form together
A
lentiform nucleus
5
Q
What is the basal ganglia important for
A
- it is important for initiation of movement
- it has a role in processing information relating to emotion, motivation and cognition
6
Q
What is the cerebellum important for
A
sensory motor coordination of ongoing movement, it contacts the descending systems
7
Q
where are the upper motor neurones
A
- they are in the motor cortex in the brain and the brainstem centres
8
Q
What does the basal ganglia do in terms of movement
A
- Initiates and maintenance of motor action
- Inhibits antagonistic and unnecessary movements
- Switch motor programs – e.g. stop or start a movement
9
Q
describe the structure of the caudate nuclei
A
- C shaped nuclei comprised of a globular head, tapering body and a down curving tail
- Head regions curves and extends to form an elongated body, tapering at the tail and ending in a temporal lobe
10
Q
describe the structure of the putamen
A
- Large rounded nuclei located at the base of the forebrain
- Connected to caudate nucleus at the head region of the caudate
11
Q
How is the putamen connected to the caudate
A
- it is connected to the caudate nucleus at the head region of the caudate
12
Q
Describe the structure of the globus pallidus
A
- Comprised of an internal and external segment
- Internal segment (GPi) sends output to the thalamus.
- External segment (GPe) relays information between other basal ganglia nuclei and GPi.
13
Q
describe the internal and external segement of the globus pallidus
A
- Internal segment (GPi) sends output to the thalamus.
- External segment (GPe) relays information between other basal ganglia nuclei and GPi.
14
Q
describe the structure of the internal capsule
A
- White matter structures composed of bundles of myelinated fibres
- Separates lentiform nucleus from the caudate nucleus and thalamus
15
Q
What does the internal capulse separate
A
- Separates lentiform nucleus from the caudate nucleus and thalamus
16
Q
name the blood supply to the
- caduate
- putamen
- globus pallidus
- internal capsule
A
Caudate
- Middle cerebral artery (body)
- Anterior cerebral artery (anterior)
Putamen
- Middle cerebral artery
- Anterior cerebral artery (anterior)
Globus pallidus
- Middle ceberal artery
- Anterior choroidal
Internal capsule
- Middle cerebral artery (middle)
- anterior cerebral artery (anterior limb)
- anterior choroidal (posterior limb)
17
Q
Where does the neural projections into the caudate and putamen come from
A
- mostly come from the cerebral cortex in particular the frontal and parietal cortex
- there is input from the temporal and occipital cortex, but it is mainly from the frontal and parietal cortex
- there is also input from the substantia nigra pars compacta - this provides dopamine input into the caudate and putamen
18
Q
where is the majority of neural projects into the caudate
A
- it is from the frontal cortex
19
Q
almost all regions of the cerebral cortex….
A
• Almost all regions of the cerebral cortex project directly to the caudate nucleus and putamen
20
Q
what are projections into the caudate nucleus and putamen referred to as
A
corticostriatal pathway
21
Q
where is the substantia nigra pars compacta located
A
- it is located into the midbrain
22
Q
what is the function of the substantia nigra pars compacta
A
• Provides dopaminergic input to the caudate nucleus and putamen.
23
Q
What are projections into the caudate and putamen from the substantia nigra pars compacta called
A
• Projections are referred to as the nigrostriatal pathway.
24
Q
what are the majority of neurones called in the caudate and putamen
A
- Approximately 75% of neurones in the caudate and putamen (corpus striatum) are medium spiny neuornes
25
what is the key neurone type of the corpus striatum
- medium spiny neurones
26
What do the medium spiny neurones in the corpus striatium do
- Large dendritic trees of medium spiny neurones allow the integration of convergent inputs from
- Cortical neurones (glutmatergic)
substantia nigra pars compacta neurones (dopaminergic)
- Local circuit neurones in corpus striatum (GABAergic)
27
where do axons that arise from the medium spiny neurones converge
Axons arising from medium spiny neurones converge of neurones in the Globus pallidus and substantia nigra pars reticulata
28
what is output from the basal ganglia and where do the projections go
Output from the basal ganglia
- The globus pallidus and substantia nigra pars reticulata comprised the output one of the corpus striatium
Projections from the output zone are to the
- Subthalamic nuelcus
- VA/VL thalamic nucleus complex – in particular the ventral anterior and ventral lateral complex
- Superior colliculus – this controls eye movement
29
where are the subthalamic nuclei, where do they receive input from and project output to
- Small paired nuclei located below the thalamus
- These receive input from the cerebral cortex and external Globus pallidus
- Projects to the internal Globus pallidus and substantia nigra pars reticulata
30
where do the VA/VL thalamic nucleus comprise of, where are the inputs and where are the output
* The VA/VL complex comprises the major site of basal ganglia outflow.
* Receives input from internal globus pallidus (GPi).
* Projects directly to motor areas of cerebral cortex.
* Thus, completes a vast loop of neural circuitry in the cerebral cortex.
31
How can we summarise the connections and how are movement intiated and sequened by the basal ganglia
Direct and indirect pathways
32
describe disinhibition
* Cortical input to the corpus striatum is via excitatory glutamate neurons.
* Corpus striatum and globus pallidus contain mainly inhibitory GABAergic neurons.
* When there are two inhibitory neurons in sequence, there is “inhibition of inhibition” (i.e. overall excitation).
33
what does the direct pathway do
- Provides a means for the basal ganglia to facilitate the initiation of volitional movement
34
describe the mechanism of action of the direct pathway
- Substantia nigra pars compact activates caudate/putamen via D1
- the caudate and putamen Inhibits the globus pallidus internal segment which is tonically activate
- This disinhibits the thalamus neurones which allows them to project to the frontal cortex and allows the initiation of movement
- The process of disinhibition of the thalamic neurones allows frontal cortex to become activate
- this can also happen by activation of the cerebral cortex projecting into the caudate and putamen
35
What is the indirect pathway
- Indirect pathway serves to antagonise the activity of the direct pathway. Together, they function to open or shut the gates that initiate and terminate movements.
36
describe the mechanism of action of the indirect pathway
- the substantia nigra pars compacta projects into the caudate and putamen via D1/D2
- D1 provides an excitatory signal whereas D2 provides an inhibitory signal
- the caudate and putmen inhibit both the internal and external globus pallidus segment
- the external globus pallidus segment inhibits the internal globus pallidus internal segement
- the external globus pallidus segment inhibits the subthalamic nuclei this then activates the globus pallidus internal segement
- the globus pallidus internal segment gives tonic inhibition to the VA/VL pathway
- this activates the frontal cortex
37
Describe the organisation of direct and indirect pathways
* When at rest or undergoing a repetitive movement (e.g. talking) the direct pathway is inactive and the indirect pathway is active.
* Tonic inhibitory input to the motor thalamus prevents a change in movement (i.e. you continue what you are already doing).
* When you want to change your motor program (e.g. stop or start a particular movement) the direct pathway becomes active.
38
dopamine can be both ...
- excitatory and inhibitory
39
describe what stimulates and inhibits both dopamine pathways
- D1 - D1 receptor-expressing neurons in the direct pathway are stimulated by dopamine – activates motor programme change.
- D2 - D2 receptor-expressing neurons in the indirect pathway are inhibited by dopamine – blocks motor programme change.
40
name a disease that results in hypokinetic movement
Parkinsons disease
41
what is the second most common neurodegenerative disorder
• Parkinson’s disease is the second most common neurodegenerative disorder (after Alzheimer’s disease).
42
describe the characteristics of parkinsons disease
• Parkinson’s disease can be both sporadic and inheritable.
43
what are the characertstics of parkinsons disease
- Resting tremor
- Slowness of movement (bradykinesia)
- Muscular rigidity
- Minimal facial expressions
44
Describe the cause of defects in motor function in parkinson's disease
- These are due to the loss of dopaminergic neurones in the substantia nigra pars compacta which project to and innervate the caudate and putamen
- Over approximately over 80% of dopamine neuroens have to degenerate before clinical sympotms manifest themselves
45
describe the cause of parkison's disease
- Alters basal ganglia pathway
- There is degeneration of dopamine neurones in the substantia nigra pars compact
- Therefore there is a shift in the direct and indirect pathways
- Dopamine influences the direct pathway if there is degeneration of dopamine neurones then there is a shift towards the indirect pathway
- Therefore there is increased projections to the globus pallidus external segment leading to increase projection to subthalamic nucleus therefore increased excitatory into to the Globus pallidus internal segment
- Therefore there is more tonic inhibition of the thalamus leading to decreased excitation to the frontal cortex therefore a decrease in movement happening
46
name the treatment plan of parkinson's
Early Parkinson’s with cardinal symptoms but no mediciation related complications
- Levodopa
- Dopamine agonists
- MAO-B inhibitors
Parkinson with motor and non motor complications, medication side effects and unrelieved symptoms
- COMT inhibitors
- Apomorphine
- Amatadine
47
What can happen if the balance of inhibitory signals in the direct and indirect pathways are altered?
- Hyperkinetic movement disroders such as huntingtons disease
48
name a hyperkinetic movement disorder
Huntingtons disease
49
How is huntingtons disease caused
• Inherited in an autosomal dominant manner (mutation of the huntingtin gene).
50
What is Huntingtons characterised by
I. Mood alterations (e.g. depression)
II. Personality alterations (e.g. irritability, impulsive or eccentric behaviour)
III. Defects in memory and attention
IV. Involuntary movements (hallmark of the disease)
51
What is huntingtons caused y
- Defects in motor function are due to the loss of GABAergic neurons in the corpus striatum, which project to and innervate the globus pallidus.
52
describe the types and hallmarks in huntingtons that describe the different type of involuntary movement
Chorea
- Chorea refers to rapid, involuntary, jerky-type movements
- (derived from the Greek for “to dance”).
- Rapid, involuntary, semi or non purposeful, dance-like, more distal
Athetosis
- Athetosis refers to slow, involuntary, smooth, writhing-type movements (derived from the Greek for “to throw”).
- Slow, involuntary, non purposeful, writhing, more distal
Ballismus
- Ballismus refers to rapid, involuntary, wild flinging-type movements (derived from the Greek for “not fixed”).
- Rapid, involuntary, non purposeful, wild flinging, more proximal
53
describe how the pathways are affected in Huntingtons
- In huntingtons disease there is degeneration of GABAnergic in the caudate and putamen, shifts balance from the indirect pathway to the direct pathway
- Therefore there is more activation of the direct pathway therefore there is less tonic inhibition
- Therefore less tonic inhibiton of the thalamus neurones therefore increased excitation of the frontal cortex
- Therefore increased movement
- There is increased inhibition of the subthalamic nuelcues and the globus pallidus intenral segement
