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Brain and Behaviour Year 2 > Basal Ganglia > Flashcards

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
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2
Q

What are the neural structures of the basal ganglia

A
  • Caudate
  • Putamen
  • Globus pallidus
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3
Q

What do the caudate and putamen nuclei form together

A

corpus striatum

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4
Q

What do the putamen and the globus pallidus form together

A

lentiform nucleus

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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

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6
Q

What is the cerebellum important for

A

sensory motor coordination of ongoing movement, it contacts the descending systems

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7
Q

where are the upper motor neurones

A
  • they are in the motor cortex in the brain and the brainstem centres
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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
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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
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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

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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
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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.
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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.

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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
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15
Q

What does the internal capulse separate

A
  • Separates lentiform nucleus from the caudate nucleus and thalamus
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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)
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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
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18
Q

where is the majority of neural projects into the caudate

A
  • it is from the frontal cortex
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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

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20
Q

what are projections into the caudate nucleus and putamen referred to as

A

corticostriatal pathway

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21
Q

where is the substantia nigra pars compacta located

A
  • it is located into the midbrain
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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
Q

what is the key neurone type of the corpus striatum

A
  • medium spiny neurones
26
Q

What do the medium spiny neurones in the corpus striatium do

A
  • 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
Q

where do axons that arise from the medium spiny neurones converge

A

Axons arising from medium spiny neurones converge of neurones in the Globus pallidus and substantia nigra pars reticulata

28
Q

what is output from the basal ganglia and where do the projections go

A

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
Q

where are the subthalamic nuclei, where do they receive input from and project output to

A
  • 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
Q

where do the VA/VL thalamic nucleus comprise of, where are the inputs and where are the output

A
  • 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
Q

How can we summarise the connections and how are movement intiated and sequened by the basal ganglia

A

Direct and indirect pathways

32
Q

describe disinhibition

A
  • 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
Q

what does the direct pathway do

A
  • Provides a means for the basal ganglia to facilitate the initiation of volitional movement
34
Q

describe the mechanism of action of the direct pathway

A
  • 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
Q

What is the indirect pathway

A
  • 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
Q

describe the mechanism of action of the indirect pathway

A
  • 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
Q

Describe the organisation of direct and indirect pathways

A
  • 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
Q

dopamine can be both …

A
  • excitatory and inhibitory
39
Q

describe what stimulates and inhibits both dopamine pathways

A
  • 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
Q

name a disease that results in hypokinetic movement

A

Parkinsons disease

41
Q

what is the second most common neurodegenerative disorder

A

• Parkinson’s disease is the second most common neurodegenerative disorder (after Alzheimer’s disease).

42
Q

describe the characteristics of parkinsons disease

A

• Parkinson’s disease can be both sporadic and inheritable.

43
Q

what are the characertstics of parkinsons disease

A
  • Resting tremor
  • Slowness of movement (bradykinesia)
  • Muscular rigidity
  • Minimal facial expressions
44
Q

Describe the cause of defects in motor function in parkinson’s disease

A
  • 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
Q

describe the cause of parkison’s disease

A
  • 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
Q

name the treatment plan of parkinson’s

A

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
Q

What can happen if the balance of inhibitory signals in the direct and indirect pathways are altered?

A
  • Hyperkinetic movement disroders such as huntingtons disease
48
Q

name a hyperkinetic movement disorder

A

Huntingtons disease

49
Q

How is huntingtons disease caused

A

• Inherited in an autosomal dominant manner (mutation of the huntingtin gene).

50
Q

What is Huntingtons characterised by

A

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
Q

What is huntingtons caused y

A
  • 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
Q

describe the types and hallmarks in huntingtons that describe the different type of involuntary movement

A

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
Q

describe how the pathways are affected in Huntingtons

A
  • 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

Brain and Behaviour Year 2 (36 decks)

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