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functional neuroanatomy > Week 8 - basal ganglia > Flashcards

Week 8 - basal ganglia Flashcards

1
Q

What are the four parts contributing to motor control?

A
  • spinal cord and brainstem circuits
  • descending motor control system
  • basal ganglia
  • cerebellum
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2
Q

What is the spinal cord and brainstem circuits comprised of?

A

local circuit neurons and lower motor neuons

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3
Q

What is the descending motor control system comprised of?

A
  • upper motor neurons:
  • motor cortex and brainstem centres
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4
Q

What does the motor Corte do?

A

planning, initiating and directing voluntary movements

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5
Q

What do the brainstem centres do?

A

basic movements and postural control

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6
Q

What is the function of the basal ganglia?

A

gating propter initiation of movement

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7
Q

What is the function of the cerebellum?

A

Sensory information and coordination of ongoing movement

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8
Q

What are the basal ganglia?

A
  • large and functionally diverse set of neural structures buried deep within the cerebral hemispheres
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9
Q

Function of the basal ganglia

A
  • primarily regulating movement - but also have roles processing information relating to emotion, motivation and cognition
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10
Q

What three aspects of movement does the basal ganglia do?

A
  • initiation and maintenance of motor actions
  • inhibit antagonistic and unnecessary movement
  • switch motor programs - start+ stop movement
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11
Q

What are the neural structures within the basal ganglia?

A
  • caudate
  • putamen
  • globus pallidus
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12
Q

What makes the lentiform nucleus?

A

putamen + globus pallidus

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13
Q

What makes the corpus striatum?

A

caudate + putamen

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14
Q

What are the 2 areas, the basal ganglia has functional motor associations with?

A
  • substantia nigra
  • sub thalamic nucleus
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15
Q

What is the caudate?

A
  • c-shaped nuclei located in forntal lobe
  • head region curves and extends to form elongated body tapering at tail and ending in temporal lobe
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16
Q

What is the putamen?

A
  • large, rounded nuclei located in forebrain
  • connected to caudate nucleus at head region of the caudate
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17
Q

What is the globus pallidus?

A
  • pale body
  • internal segment sends output to the thalamus
  • external segment relays info between other basal ganglia nuclei and internal globus pallidus
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18
Q

What is the internal capsule?

A
  • white matter structure (myelinated axons)
  • separates lentiform nucleus and caudate nucleus/ thalamus
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19
Q

Where do projections to the basal ganglia originate from?

A
  • cerebral cortex (ie. frontal/ pariental)
  • substantia nigra pars compacta
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20
Q

What regions of the cerebral cortex project directly to the caudate nucleus and putamen?

A

almost all

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21
Q

Where is the majority of projections from?

A

forntal and parietal cortex

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22
Q

As what are the protections form the cortex to the basal ganglia referred to?

A

corticostriatal pathway

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23
Q

Where is the substantia nigra pars compact located?

A

in the midbrain

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24
Q

What does the substantia nigra pars compacta provide?

A

dopaminergic input to caudate nucleus and putamen

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25
Q

As what are the projections form the substantia nigra pars compacta to the basal ganglia referred to?

A

nigrostriatal pathway

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26
Q

Where do the neuronal projections go to in the basal ganglia?

A

input zones

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27
Q

What are the input zones of the basal ganglia?

A

corpus striatum - made up of caudate nucleus and putamen

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28
Q

What kind of neurons are most common in the corpus striatum? (75%)

A

medium spiny neurons

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29
Q

What do the large dendritic trees of medium spiny neurons allow for in the BG?

A

integration of convergent inputs

30
Q

Where are the convergent inputs from?

A
  • cortical neurons (glutamatergic)
  • substantia nigra pars compacta neurons (dopaminergic)
  • local circuit neurons within the corpus striatum (GABAergic)
31
Q

What is the structure of the dendritic trees in the BG of medium spiny neurons?

A

axons arise from medium spiny neurons - converge on enurons in globus pallidus + substantia nigra pars reticulata

32
Q

Describe the flow of the corpus striatum convergence

A

cortex -> corpus striatum -> globus pallidus external -> globus pallidus internal or substantial nigra pars reticulata

33
Q

What is the output zone of the basal ganglia?

A
  • globus pallidus
  • substantia nigra pars reticulata
34
Q

Where do the projections from the output zone go to?

A
  • sub thalamic nucleus
  • VA/VL thalamic nuclear complex
  • superior colliculus
35
Q

What do the projections going to the superior colliculus do?

A

control eye movement

36
Q

What’re the substhalmic neuclei and where are they located?

A

small paired nuclei located below thalamus

37
Q

Describe the input and output projections of the sub thalamic nucleus

A
  • receives input form cerebral cortex and external globus pallidus
  • projects internal globus pallidus and substantial nigra pars reticulata
38
Q

What is the VA/VL thalamus complex?

A
  • comprises major site of basal ganglia outflow
  • receives input form internal globus pallidus
  • projects directly to motor areas of cerebral cortex
    -> completes vast loop of neural circuitry in the cerebral cortex
39
Q

How are connections of basal ganglia summarised and how are movements initiated and sequenced by basal ganglia?

A

direct and indirect pathways

40
Q

How does the disinhibition within direct and indirect pathways take place?

A
  • cortical input to corpus stratum via excitatory glutamate neurons
  • corpus stratum and globus pallidus contain mainly inhibitory GABAergic neurons
  • when two inhibitory neurons in sequence, there is inhibition of inhibition
41
Q

What is the excitation by double inhibition called?

A

disinhibition

42
Q

What do direct pathways provide the basal ganglia?

A

ability to facilitate initiation of volitional movement

43
Q

What is the function of indirect pathways?

A

serve to antagonise the activity of the direct pathway

44
Q

What do indirect and direct pathways allow for together?

A

initiation and termination of movements

45
Q

What pathways are active when at rest or undergoing a repetitive movement eg. talking?

A

indirect pathways (suppressing competing motor programs)

46
Q

What prevents a change in movement when at rest or talking (repetitive movement)?

A

tonic inhibitory input to VA/ VL thalamus complex prevents change in movement (ie. you continue what you are already doing)

47
Q

What happens to direct/ indirect pathways when you want to change your motor program ie. stop or start a particular movement?

A

direct pathways become active

48
Q

Direct pathways happen via:

A

caudate and putamen

49
Q

Indirect pathways happen via

A

subthalamic nucleus

50
Q

Where can D1 or D2 dopamine receptors be found?

A

in corpus striatum neurons

51
Q

what does dopamine do in relation tot he direct/ indirect pathways?

A
  • increases action of direct pathway via D1receptors
  • decreases action of indirect pathway via D2 receptors
52
Q

How does the D1 receptor modulate dopamine in the basal ganglia?

A
  • increases cAMP whilst D2 receptors decrease cAMP
  • increases sensitivity of porous stratum neurons to glutamate
  • facilities direct pathway
53
Q

How odes dopamine regulate VA/VL thalamus?

A

cortical glutamatergic input -> corpus striatum D1 neurons activated -> increased inhibition -> globus pallidus internal -> decreased inhibition -> VA/ VL thalamus

54
Q

How do direct pathways activate motor program change?

A

via D1 receptors that are activated by dopamine

55
Q

How do indirect pathways block motor program change?

A

via D2 receptors that are depressed by dopamine

56
Q

Overall dopamine:

A

gives ability to start , stop, change motor programs at will

57
Q

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

A

hypo (low) kinetic movement disorders (eg. Parkinson’s)
hyper kinetic movement disorders (eg. Huntingtons)

58
Q

What characterises Parkinsons?

A

(can be sporadic and inheritable)
- resenting tremor
- slowness of movement
- muscular rigidity
- postural instability

59
Q

What causes the defects in motor function in Parkinsons?

A

loss of dopaminergic neurons in the substantia nigra pars compacta, which protect to and innervate the caudate and putamen

60
Q

How many dopaminergic neurons have to degenerate before the clinical signs of disease manifest themselves?

A

80%

61
Q

What is the difference in a picture of the midbrain of a PD patient and a normal patient?

A

substantia nigra will not be stained black - lack of dopaminergic neurons

62
Q

What does Parkinson do in terms of indirect/ direct pathways?

A

shifts the balance in favour of activity in indirect

63
Q

What is an example of hyperkinetic movement disorders?

A

Huntingtons

64
Q

Can Huntingtons be inherited?

A

yes - autosomal dominant

65
Q

What is Huntingtons disease characterised by?

A
  1. mood alterations - eg. depression
  2. personality alterations - eg. irritability, impulsive or eccentric behaviour
  3. defects in memory and attention
  4. involuntary movements (hallmark)
66
Q

What are the defects in motor function in Huntingtons disease caused by?

A

loss of GABAergic neurons in corpus striatum, project to innervate flubs pallidus

67
Q

What is the difference between the corpus striatum of a HD patient and a normal patient?

A

enlargement of ventricles and shrinkage of basal ganglia

68
Q

chorea

A
  • rapid
    involuntary
  • semi/ non purposeful
  • dance like
  • distal
69
Q

athetosis

A
  • slow
  • involuntary
  • non purposeful
  • writhing
  • more distal
70
Q

Ballismus

A
  • rapid
  • involuntary
  • non-purposeful
  • wild flinging
  • more proximal
71
Q

What does Huntingtons disease result in in terms of direct/ indirect pathway?

A

shifts balance in favour of activity in direct pathway

72
Q
A

functional neuroanatomy (16 decks)

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