Week 8 - basal ganglia Flashcards
(72 cards)
1
Q
What are the four parts contributing to motor control?
A
- spinal cord and brainstem circuits
- descending motor control system
- basal ganglia
- cerebellum
2
Q
What is the spinal cord and brainstem circuits comprised of?
A
local circuit neurons and lower motor neuons
3
Q
What is the descending motor control system comprised of?
A
- upper motor neurons:
- motor cortex and brainstem centres
4
Q
What does the motor Corte do?
A
planning, initiating and directing voluntary movements
5
Q
What do the brainstem centres do?
A
basic movements and postural control
6
Q
What is the function of the basal ganglia?
A
gating propter initiation of movement
7
Q
What is the function of the cerebellum?
A
Sensory information and coordination of ongoing movement
8
Q
What are the basal ganglia?
A
- large and functionally diverse set of neural structures buried deep within the cerebral hemispheres
9
Q
Function of the basal ganglia
A
- primarily regulating movement - but also have roles processing information relating to emotion, motivation and cognition
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
11
Q
What are the neural structures within the basal ganglia?
A
- caudate
- putamen
- globus pallidus
12
Q
What makes the lentiform nucleus?
A
putamen + globus pallidus
13
Q
What makes the corpus striatum?
A
caudate + putamen
14
Q
What are the 2 areas, the basal ganglia has functional motor associations with?
A
- substantia nigra
- sub thalamic nucleus
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
16
Q
What is the putamen?
A
- large, rounded nuclei located in forebrain
- connected to caudate nucleus at head region of the caudate
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
18
Q
What is the internal capsule?
A
- white matter structure (myelinated axons)
- separates lentiform nucleus and caudate nucleus/ thalamus
19
Q
Where do projections to the basal ganglia originate from?
A
- cerebral cortex (ie. frontal/ pariental)
- substantia nigra pars compacta
20
Q
What regions of the cerebral cortex project directly to the caudate nucleus and putamen?
A
almost all
21
Q
Where is the majority of projections from?
A
forntal and parietal cortex
22
Q
As what are the protections form the cortex to the basal ganglia referred to?
A
corticostriatal pathway
23
Q
Where is the substantia nigra pars compact located?
A
in the midbrain
24
Q
What does the substantia nigra pars compacta provide?
A
dopaminergic input to caudate nucleus and putamen
25
As what are the projections form the substantia nigra pars compacta to the basal ganglia referred to?
nigrostriatal pathway
26
Where do the neuronal projections go to in the basal ganglia?
input zones
27
What are the input zones of the basal ganglia?
corpus striatum - made up of caudate nucleus and putamen
28
What kind of neurons are most common in the corpus striatum? (75%)
medium spiny neurons
29
What do the large dendritic trees of medium spiny neurons allow for in the BG?
integration of convergent inputs
30
Where are the convergent inputs from?
- cortical neurons (glutamatergic)
- substantia nigra pars compacta neurons (dopaminergic)
- local circuit neurons within the corpus striatum (GABAergic)
31
What is the structure of the dendritic trees in the BG of medium spiny neurons?
axons arise from medium spiny neurons - converge on enurons in globus pallidus + substantia nigra pars reticulata
32
Describe the flow of the corpus striatum convergence
cortex -> corpus striatum -> globus pallidus external -> globus pallidus internal or substantial nigra pars reticulata
33
What is the output zone of the basal ganglia?
- globus pallidus
- substantia nigra pars reticulata
34
Where do the projections from the output zone go to?
- sub thalamic nucleus
- VA/VL thalamic nuclear complex
- superior colliculus
35
What do the projections going to the superior colliculus do?
control eye movement
36
What're the substhalmic neuclei and where are they located?
small paired nuclei located below thalamus
37
Describe the input and output projections of the sub thalamic nucleus
- receives input form cerebral cortex and external globus pallidus
- projects internal globus pallidus and substantial nigra pars reticulata
38
What is the VA/VL thalamus complex?
- 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
How are connections of basal ganglia summarised and how are movements initiated and sequenced by basal ganglia?
direct and indirect pathways
40
How does the disinhibition within direct and indirect pathways take place?
- 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
What is the excitation by double inhibition called?
disinhibition
42
What do direct pathways provide the basal ganglia?
ability to facilitate initiation of volitional movement
43
What is the function of indirect pathways?
serve to antagonise the activity of the direct pathway
44
What do indirect and direct pathways allow for together?
initiation and termination of movements
45
What pathways are active when at rest or undergoing a repetitive movement eg. talking?
indirect pathways (suppressing competing motor programs)
46
What prevents a change in movement when at rest or talking (repetitive movement)?
tonic inhibitory input to VA/ VL thalamus complex prevents change in movement (ie. you continue what you are already doing)
47
What happens to direct/ indirect pathways when you want to change your motor program ie. stop or start a particular movement?
direct pathways become active
48
Direct pathways happen via:
caudate and putamen
49
Indirect pathways happen via
subthalamic nucleus
50
Where can D1 or D2 dopamine receptors be found?
in corpus striatum neurons
51
what does dopamine do in relation tot he direct/ indirect pathways?
- increases action of direct pathway via D1receptors
- decreases action of indirect pathway via D2 receptors
52
How does the D1 receptor modulate dopamine in the basal ganglia?
- increases cAMP whilst D2 receptors decrease cAMP
- increases sensitivity of porous stratum neurons to glutamate
- facilities direct pathway
53
How odes dopamine regulate VA/VL thalamus?
cortical glutamatergic input -> corpus striatum D1 neurons activated -> increased inhibition -> globus pallidus internal -> decreased inhibition -> VA/ VL thalamus
54
How do direct pathways activate motor program change?
via D1 receptors that are activated by dopamine
55
How do indirect pathways block motor program change?
via D2 receptors that are depressed by dopamine
56
Overall dopamine:
gives ability to start , stop, change motor programs at will
57
What can happen if the balance of inhibitory signal in the direct and indirect pathways are altered?
hypo (low) kinetic movement disorders (eg. Parkinson's)
hyper kinetic movement disorders (eg. Huntingtons)
58
What characterises Parkinsons?
(can be sporadic and inheritable)
- resenting tremor
- slowness of movement
- muscular rigidity
- postural instability
59
What causes the defects in motor function in Parkinsons?
loss of dopaminergic neurons in the substantia nigra pars compacta, which protect to and innervate the caudate and putamen
60
How many dopaminergic neurons have to degenerate before the clinical signs of disease manifest themselves?
80%
61
What is the difference in a picture of the midbrain of a PD patient and a normal patient?
substantia nigra will not be stained black - lack of dopaminergic neurons
62
What does Parkinson do in terms of indirect/ direct pathways?
shifts the balance in favour of activity in indirect
63
What is an example of hyperkinetic movement disorders?
Huntingtons
64
Can Huntingtons be inherited?
yes - autosomal dominant
65
What is Huntingtons disease characterised by?
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
What are the defects in motor function in Huntingtons disease caused by?
loss of GABAergic neurons in corpus striatum, project to innervate flubs pallidus
67
What is the difference between the corpus striatum of a HD patient and a normal patient?
enlargement of ventricles and shrinkage of basal ganglia
68
chorea
- rapid
involuntary
- semi/ non purposeful
- dance like
- distal
69
athetosis
- slow
- involuntary
- non purposeful
- writhing
- more distal
70
Ballismus
- rapid
- involuntary
- non-purposeful
- wild flinging
- more proximal
71
What does Huntingtons disease result in in terms of direct/ indirect pathway?
shifts balance in favour of activity in direct pathway
72
