Motor Control Flashcards
1
Q
Levels of the motor system
A
High
Middle
Low
2
Q
Function of the higher level of the motor system
A
Strategy
3
Q
Function of the middle level of the motor system
A
Tactics
4
Q
Function of the low level of the motor system
A
Execution
5
Q
Structures of the higher level of the motor system
A
Association neocortex
Basal ganglion
6
Q
Structures of the middle level of the motor system
A
Motor cortex
Cerebellum
7
Q
Structures of the lower level of the motor system
A
Brain stem
Spinal cord
8
Q
What is the strategy?
A
The goal and the movement strategy best to achieve that goal
9
Q
What are the tactics?
A
The sequence of spatiotemporal muscle contractions to achieve a goal smoothly and accurately
10
Q
What is the execution?
A
Activation of motor neurone and interneuron pools to generate a goal directed movement
11
Q
How is the brain connected to the spinal cord?
A
Lateral pathways
Ventromedial pathways
12
Q
Function of lateral pathways
A
Control voluntary movements of distal muscles
13
Q
Lateral pathways are under direct control of what?
A
Direct cortical control
14
Q
Function of ventromedial pathways
A
Control posture and locomotion
15
Q
What are ventromedial pathways under control of?
A
Brainstem
16
Q
What are the lateral pathways?
A
Corticospinal tract
Rubrospinal tract
17
Q
What are the ventromedial pathways?
A
Tectospinal tract
Vestibulospinal tract
Pontine reticulospinal tract
Medullary reticulospinal tract
18
Q
What is the most important lateral pathway?
A
Corticospinal tract
19
Q
Where does the corticospinal tract originate from?
A
2/3rds in areas 4 and 6 of the frontal motor cortex
Rest is somatosensory
20
Q
Journey of the Corticospinal tract
A
At the medulla/spinal cord junction the CST crosses over (decussates) so that
- the right motor cortex controls the left side and the left motor cortex controls the right side
CST axons synapse on the ventral horn motor neurones and interneurons to control muscles
21
Q
Where does the rubrospinal tract start?
A
Red nucleus of the midbrain
22
Q
What are the inputs to the rubrospinal tract?
A
Same as the CST
23
Q
Size difference CST vs RST
A
CST - larger, longer
24
Q
If you have a lesion in CST and RST, what would happen?
A
Fine movements of arms and hands lost
Cant move shoulders, elbows, wrists and fingers indepdently
25
If you have a lesion in the CST alone, what would happen? Why?
Same deficits, but after a few months functions reappear.
| Happens because been taken over by the RST
26
What do the RST and the CST have?
Duality of function
27
What are the two ventromedial pathways which control posture and locomotion?
Vestibulospinal tract
| Tectospinal tract
28
Function of Vestibulospinal tract
Stabilises head and neck
29
Function of the tectospinal tract
Ensures eyes remain stable as the body moves
30
When are TST and VST critical?
When the body is carrying out complicated body movements
31
Where does the VST originate?
Vestibular nucleus
32
Where does the TST originate?
Superior colliculus
33
Which ventromedial pathways control the trunk and antigravity muscles?
Pontine and medullary reticulospinal tracts
34
Where do the pontine and medullary reticulospinal tracts originate?
Brainstem
35
How do the pontine and medullary reticulospinal tracts work?
Use sensory info about balance, body position and vision
| Reflexly maintain balance and body position
36
What do antigravity muscles do?
Hold the body up
37
How does the lateral pathways work?
Motor cortex directly activates spinal motorneurones and frees them from reflex control by communicating via nuclei of ventromedial pathways
38
What parts of the brain plan and control precise voluntary movements?
Primary motor cortex and pre motor areas
39
What do UMNs in the cortex and brainstem target?
LMN in the spinal cord
| Some also form circuits that control reflexes such as the stretch reflex and withdrawal reflex
40
Medial tracts in the spinal c ord control what?
Axial and proximal limb muscles
41
Lateral tracts in the spinal cord control what?
Distal limb muscles
42
Medial tracts from the brainstem control what?
Posture balance and orientating mechanisms
43
Lateral tracts from the cortex control what?
Precise skilled voluntary movements
44
Where is the primary motor cortex found?
The Precentral gyrus
45
Where do the mosaic of premotor areas lie?
Rostrally
46
On the motor homunculus, which part of the body is the most medial?
Toes
47
On the motor homunculus, which part of the body is the most lateral?
Tongue (swallowing)
48
Order of the body parts on the motor homunculus, from medial to lateral
```
Toes
Ankle
Knees
Hip
Trunk
Shoulder
Elbow
Wrist
Hand
Little finger
Ring finger
Middle finger
Index finger
Thumb
Neck
Eyebrow
Eyelid and eyeball
Face
Lips
Jaw
Tongue
Swallowing
```
49
What is penfield electrical stimulation for?
In epileptics used to decide brain areas to be spared surgically
50
What area of the brain is the primary motor cortex?
Area 4
51
What does area 6 contain?
Neurones that drive complex movements of either side of the body
- premotor area
- supplementary motor area
52
What does the supplementary motor area innervate?
Distal motor units directly
53
What does the pre-motor area innervate?
Reticulospinal neurones innervating proximal motor units
54
Is the somatotropic motor map precise? Why?
No
| Does not represent UMNs causing individual muscle movements
55
What does microstimulation in specific areas of the primary motor cortex cause?
Coordinated movements of hand and mouth
| Movements that bring hands into central space to insert/manipulate objects
56
How is the mental image of the body in space generated?
Somatosensory input
Visual input
Proprioceptive input
57
Where are decisions made about what actions/movements to take and their likely outcome?
Prefrontal or parietal cortex
58
When do decision making neurones in cortical PMA fire?
BEFORE a movement (one second before)
59
When do PMA "mirror neurones" fire?
When self or others perform specific actions - the movement is imagined and mentally rehearsed
When others make the same specific movement; this allows understanding of actions or intentions of others
60
What may mirror neurones underpin?
Emotions
| Empathy
61
How is overall movement direction encoded?
By the integrated activity of all the neurones
62
What does a change in body position cause? (Feedback mechanism)
Rapid compensatory feedback messages from the brainstem vestibular nuclei to spinal cord motor neurones to correct postural instability
63
How do feedforward mechanisms work?
Before movements begin, the brainstem reticular formation nuclei (controlled by the cortex) initiate feedforward anticipatory maintenance of body posture
64
What would cortical damage cause?
```
Immediate flaccidity of contralateral muscles
Initial hypotonic "spinal shock"
Days later spinal circuits regain function
Spasticity
- increased muscle tone
- hyperactive stretch reflex
- clonus
Loss of fine finger movements
```
65
In Babinksis sign, what does extension indicate?
Both indicate incomplete upper control of spinal circuits
66
What selects and initiates willed movements?
Basal ganglia
67
Where does major subcortical input to area 6 come from? What is this input called and where does it arise from?
Ventral lateral nucleus in the dorsal thalamus
| The input is called VLo and arises from basal ganglion
68
What is the basal ganglia targets of?
Frontal Cortex
Prefrontal cortex
Parietal cortex
69
What is the main component of basal ganglia?
Corpus striatum
70
Features of corpus striatum
Includes two principle nuclei (caudate and putamen)
| The input zone of the basal ganglia
71
Where does corpus striatum receive input from?
All over the cortex via the corticostriatal pathway
72
What information do the putamen and caudate receive?
Medium spiny neurones which contain excitatory (glutamatergic) cortical inputs on dendrites
73
Features of the cortical axons in basal ganglia
Inhibitors (GABAergic) and project to globus pallidus and to substantia nigra pars reticulata
74
When does the putamen fire?
Before limb / trunk movements
75
When does the caudate fire?
Before eye movements
76
What is the motor loop?
Cortex - basal ganglia - cortex
77
What is the cortex to putamen?
Excitatory
78
What is the putamen to globus pallidus?
Inhibitory
79
What is the globus pallidus to VLo neurones?
Inhibitory
80
What is the VLo to the SMA?
Excitatory
81
What is the functional consequence of cortical activation of putamen?
Excitation
82
Why does cortical activation of the putamen boost cortical excitation?
At rest globus pallidus neurones are spontaneously active and inhibit VL
Cortical excitation excites the putamen
Inhibits globus pallidus which therefore releases VLo which boots SMA activity
83
What may cause a "go" signal" for voluntary movement?
When the SMA is boosted beyond a threshold level by activity coming through the basal ganglia funnel
84
What can cortical excitation of the putamen act as?
A positive feedback loop focussing or funnelling activation of widespread cortical areas onto cortical SMA
85
What is the direct pathway loop in the basal ganglia?
Acts as a positive feedback loop, a GO signal to the SMA in the cortex
- enhances initiation of movements by the SMA
- Globus pallidus neurones are spontaneously active at rest so they tonically inhibit (restrain) VL thalamus
- input from the cortex releases this inhibition
86
Function of the indirect pathway loop in the basal ganglia
Antagonises the direct route
87
How does the indirect pathway loop in the basal ganglia work?
Striatum inhibits GPe (globus pallidus external) which then inhibits both GPi (GP internal) and STN (subthalamic nuclei)
Cortex excites STN; this excites Gpi; which inhibits the thalamus
Direct pathway selects specific motor actions, indirect pathway suppresses competing/inappropriate action
88
What % of people > 60 y/o have parkinsons?
1%
89
Presentation of parkinsons
Hypokinesia
90
What is hypokinesia?
Slowness
Difficult to make voluntary movements
Increased muscle tone (ridigity)
Tremors of hand and jaw
91
Pathology of Parkinsons
Degeneration of neurones in the substantia nigra (SN) and their dopaminergic (excitatory inputs) to the striatum
The depletion of dopamine closes down activation of focused motor activities that funnel through the thalamus to the SMA
92
Function of dopamine in basal ganglia
Can enhance cortical inputs through the "direct pathway" and suppress inputs through "indirect" pathway
93
Presentation of Huntingtons disease
Hyperkinesia
Dementia
Personality disorders
Chorea
94
How do people get huntingtons?
Hereditary
95
Features of chorea caused by Huntingtons
Spontaneous
Uncontrolled
Rapid flicks and major movements of no purpose
96
Pathology of Huntingtons
```
Genetic
Profound loss of
- caudate
- putamen
- globus pallidus
```
97
What % of the brain does the cerebellum make up?
10%
98
What % of total CNS neurones does the cerebellum contain?
50%
99
Alcohol effect on cerebellum
Depresses cerebellar circuits
100
Function of the cortico-ponto-cerebellae projection
Connects cortex, pontine nuclei and cerebellum
101
What makes up parts of the huge ponto-cerebellae projection?
Layer 5
Areas 4 and 6
Somatosensory cortex
102
Function of the cerebellum back to cortex via ventrolateral thalamus
Instructs direction, timing and force
103
How does motor loop for voluntary movement through basal ganglia and VLo undergo ongoing refinement?
Involvement of feedback loop through pons, cerebellum, thalamus and back to cortex
