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Motor Systems Flashcards

1
Q

Which regions of the cortex are involved in motor control?

A

The frontal lobe

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2
Q

How does the role of the cortex change as you get more anterior?

A

More complex/abstract its role in movement is

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3
Q

Where is the primary motor cortex?

A

Area 4

Immediately anterior to central sulcus

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4
Q

What do lesions to the primary motor cortex result in?

A

Paralysis
Paresis of specific muscle groups
May be some recovery of function (cortical plasticity) but larger lesions = more muscle groups involved = recovery less likely

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5
Q

What areas do strokes affect?

A

Always involve multiple cortical areas

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6
Q

What would a stroke occluding the middle cerebral artery affect/result in?

A

Almost all of one side of frontal lobe

Severe motor disability in contralateral body except lower limb as supplied by anterior cerebral artery

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7
Q

What would infarction of proximal segment of middle cerebral artery affect?

A

Blood supply to basal ganglia via lenticulostriate arteries
Blood supply to motor cortex
More disabling than stroke affecting distal segment (M3)

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8
Q

What are areas 6&8?

A

Premotor cortex and supplementary motor cortex

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9
Q

What would damage to areas 6 & 8 result in?

A

motor apraxia

  • normal reflexes
  • no muscle weakness
  • difficulty performing complex motor tasks
  • damage to 1 side (stroke) may produce minimal symptoms as contralateral area can take over some functions
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10
Q

What are areas 7 & 19?

A

Posterior parietal cortex

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11
Q

What would damage to areas 7 & 19 result in?

A

Sensory apraxia

  • difficulty performing complex motor tasks when triggered by sensory input
  • not strictly a motor deficit but difficulty linking sensory input to motor system
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12
Q

What is the role of the frontal eye fields?

A

Motor control of extraocular eye muscles

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13
Q

What is the role of the Broca’s area?

A

Motor control of muscles regulating speech

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14
Q

What does damage to Broca’s area lead to?

A

motor aphasia
difficulty generating speech motor outputs
difficulty linking word strings into complex sentences

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15
Q

What is oculomotor apraxia?

A

Difficulty moving eyes horizontally and quickly
may have to turn head to compensate for lack of eye movement
- can be caused by bilateral lesions of frontal eye fields which controls complex voluntary eye movements

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16
Q

What is the role of the corticobulbospinal tract?

A

Axons send commands down to spinal cord

  • modulate sensory input
  • modulate spinal reflexes
  • 40% arise from anterior parietal lobe (somatosensory cortex) and so parietal lobe involved in motor control
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17
Q

What are areas 9 & 10?

A 
Dorsolateral Prefrontal cortex
Planning of movement
Complex relationship with movement
Evaluate different possible future actions and decide which is best
Problem solving
judgement
executive functions
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18
Q

What would damage to areas 9 & 10 result in?

A

Apathy
Personality changes
Lack of ability to plan/sequence actions or tasks
Poor working memory

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19
Q

What would be the clinical difference between the left hemisphere of areas 9 & 10 being damaged and the right?

A

Left - poor working memory for verbal info.

Right - poor working memory for spatial info.

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20
Q

How are areas 9 & 10 commonly damaged?

A

With impact to the frontal bone - in a road traffic accident or blow to the head (contusions)

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21
Q

What is a contusion?

A

Brain bruising

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22
Q

What is area 11?

A

Orbitofrontal cortex

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23
Q

What is the function of area 11?

A

Concerned with control/inhibition of motor responses associated with the limbic system
- responses to hunger, thirst, sexual drives

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24
Q

What does damage to area 11 lead to?

A

(orbital damage)

  • disinhibition of responses to hunger/thirst/sexual drives = pseudopsychopathic behaviour
  • impulsiveness, jocular attitude, sexual disinhibition, complete lack of concern for others
  • orbital personality
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25
What is the motor hierarchy in the frontal lobe?
- Area 11/ 9 & 10 - Areas 6 & 8 - Area 4 /frontal eye fields/broca's/primary motor cortex - Corticobulbospinal tract/1,2,3 - Motor neurons in spinal cord
26
How does the basal ganglia connect to lower motor neurons?
The motor thalamus (VL and VA thalamic nuclei) is only route for motor commands to travel from basal ganglia and cerebellum to CSP tract and LMN
27
Where is the corticobulbospinal tract particularly vulnerable to damage by stroke?
When it courses through the internal capsule on its way to the brainstem
28
Where does the corticobulbar component of the corticobulbospinal tract terminate?
- on CN V (trigeminal) and VII (facial) for cortical control of muscles of head - on oculomotor nuclei : III, IV & VI for eye movement control - cells of pontine nuclei - reticular formation - red nucleus (in midbrain)
29
Where does the corticospinal component of the corticobulbospinal tract travel?
Continues on to lower medulla -> decussates to opposite side -> forms large lateral corticospinal tract and small medial corticospinal tract
30
Where does motor decussation occur?
In upper spinal cord | C1-C5
31
What happens if the brain is injured above the spinal cord/medulla junction?
Motor deficit is on the opposite side - if injury is in the spinal cord = motor deficit on the same side
32
Where does the lateral corticospinal tract run?
In dorsolateral cord | Near motor neurons which supply the distal muscles
33
Where does the anterior corticospinal tract run?
In the medial ventral cord Only in cervical cord Controls voluntary movements of the neck
34
What does the corticospinal tract have connections with?
Monosynaptic connections with motor neurons of thumb and digits only - other muscles motor actions mediated by CST acting on spinal interneurons
35
What does damage to the corticospinal tract in the spinal cord cause?
Loss of control of hand and fingers | Posture/locomotion and gait not lost
36
What is the extrapyramidal system?
Other descending tracts mediating motor functions of posture, locomotion and gait - originate from groups of cell bodies in the brainstem
37
What are the main components of the extrapyramidal system?
- lateral vestibulospinal tract | - reticulospinal tracts
38
What is the function of the lateral vestibulospinal tract?
Controls posture and balance | - tonically active during upright posture
39
What is the pathway of the lateral vestibulospinal tract?
- originates in the vestibular nuclei in upper medulla/lower pons - projects ipsilaterally to antigravity muscles
40
What is the function of the reticulospinal tract?
- general arousal of spinal cord - autonomical control driving sympathetic preganglionic neurons - drive to respiration via phrenic nerve
41
What is the pathway of the reticulospinal tract?
Arises in the reticular formation of the pons and medulla | - projects bilaterally down spinal cord
42
What is the function of the rubrospinal cord?
Carries cerebellar commands to the spinal cord
43
What is the pathway of the rubrospinal cord?
Orign in the red nucleus of the brainstem | Receives main input from the cerebellum
44
What is different about the rubrospinal tract in males?
It is vestigial - atrophied, remnant left
45
What is the red nucelus?
- large nucleus in midbrain | - gives rise to rubrospinal tract and large ascending projection to motor thalamus
46
What are the minor extrapyramidal pathways?
- tectospinal tract | - medial vestibulospinal tract
47
What is the function of the tectospinal tract?
Coordinates voluntary head and eye movements | - activates reflex movements of the head in response to visual and auditory stimuli
48
What is the pathway of the tectospinal tract?
Originates in the superior colliculus - projects to the contralateral cervical spinal cord - terminates in rexed laminae VI, VII, VIII
49
What is the function of the superior colliculus?
- also called the optic tectum | - receives afferents from the retina
50
What is the function of the medial vestibulospinal tract?
Continuation of the DCML - mediates reflex co-ordination of the head and neck muscles with the extraocular eye muscles to maintain objects in view despite body movements
51
Which upper motor neurons act directly on lower motor neurons in the cord?
Neurons driving the muscles of the thumb and fingers (and lips and tongue) - major descending motor tracts act on interneurons in cord to modulate strength and activity of reflex pathways instead
52
What is spasticity?
Abnormally increased muscle tone - muscles have increased tendon reflexes - characteristsic of UMN lesion
53
What is an example of an UMN lesion?
Damage to motor cortex or any descending tract
54
What is clonus?
Series of jerky contractions of a particular muscle following sudden stretching of it
55
What is hyper-reflexia?
Abnormally/pathologically brisk tendon reflex seen in one or more muscles
56
What are some severe signs of motor system damage?
Decorticate and decerebate posturing
57
What are the features of decorticate posturing?
Arms are adducted and flexed Wrists and fingers flexed on the chest Legs may be internally rotated and stiffly extended Feet may be plantar flexed
58
What does decorticate posture indicate?
Damage to the corticospinal tract in the midbrain - more favourable than decerebrate but still very severe - seen in unconscious patients - may progress to decerebrate or may alternate - can occur on one or both sides of the body
59
What are the features of decerebrate posturing?
``` Arms adducted and extended Wrists pronated Fingers flexed Legs may be internally rotated and stiffly extended Feet may be plantar flexed ```
60
What would decerebate posturing indicate?
Severe injury to the brain at the level of the brainstem - damage to corticospinal and rubrospinal tracts - due to excessive activity (disinhibition) in the extrapyramidal system - mainly due to vestibulospinal tract - only in unconscious patients
61
How can vestibulospinal tract disinhibition cause decerebrate posture?
Normally vestibulospinal tract is under tonic inhibition by corticobulbospinal tract and red nucleus - red nucleus damage by severe midbrain injury = decerebrate posturing
62
What does a discrete acute lesion lead to?
Initial paralysis Followed by variable degree of recovery During recovering - weakness, clumsiness, fatigue of movements
63
What is plasticity in the cortex?
Allows recovery | After lesion muscles may be driven by cells from a different part of the cortex as the homunculus has changed
64
What do larger lesions lead to?
Slower recovery Permanent loss of certain movement Increased weakness, clumsiness and fatigue
65
What do small lesions lead to?
Good recovery of motor skills | Motor weakness and quick fatigue always present
66
What is hemiplegic dystonia?
Persisting spasticity following motor cortex lesion Combined with motor weakness Persistent flexion of arms and extension of legs
67
What is the clasp knife reflex characteristic of?
Chronic cerebral motor lesions
68
What is spinal shock?
Condition which occurs after an acute damage to the cord including descending tract damage
69
What are the acute effects of spinal shock?
Paralysis/paresis Reduced reflex responses in all muscles below injury region If severe - all reflexes below lesion level are inactive
70
What are the chronic effects of spinal shock?
``` Eventually wears off Weak monosynaptic reflexes appear Crossed extensor reflexes may recover Severe - reflexes not controlled by brain so become exaggerated and hyperactive (hyper-reflexia) Clonus Babinski sign present ```
71
What is the difference between an UMN lesion and a LMN lesion?
UMN lesion: - in CNS - motor cortex, corticospinal tract or other motor tracts involved - groups of muscles affected - paralysis of voluntary movements - increased muscle tone - hyperactive reflexes - positive Babinski - atrophy - spastic paralysis LMN lesion: - CNS or PNS - involves spinal cord, brainstem, alpha motor neurons, peripheral motor axons - affects muscles innervated by damaged motorneuron/axon - paralysis of voluntary movements - decreased muscle tone - decreased/absent reflexes - decreased/absent Babinski - atrophy of muscles - flaccid paralysis
72
In spinal injury which tracts are responsible for which symptoms?
Injury to: - corticospinal: paralysis/weakness of voluntary movement, hyperactive tendon reflexes - reticulospinal: loss of bladder/bowel control, poor gait, loss of temp. regulation, loss of blood pressure regulation Vestibulospinal: loss of balance, poor gait

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