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BB2 > Motor Systems > Flashcards

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
Q

What is the motor hierarchy in the frontal lobe?

A
  • 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
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26
Q

How does the basal ganglia connect to lower motor neurons?

A

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

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27
Q

Where is the corticobulbospinal tract particularly vulnerable to damage by stroke?

A

When it courses through the internal capsule on its way to the brainstem

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28
Q

Where does the corticobulbar component of the corticobulbospinal tract terminate?

A
  • 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)
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29
Q

Where does the corticospinal component of the corticobulbospinal tract travel?

A

Continues on to lower medulla -> decussates to opposite side -> forms large lateral corticospinal tract and small medial corticospinal tract

30
Q

Where does motor decussation occur?

A

In upper spinal cord

C1-C5

31
Q

What happens if the brain is injured above the spinal cord/medulla junction?

A

Motor deficit is on the opposite side

  • if injury is in the spinal cord = motor deficit on the same side
32
Q

Where does the lateral corticospinal tract run?

A

In dorsolateral cord

Near motor neurons which supply the distal muscles

33
Q

Where does the anterior corticospinal tract run?

A

In the medial ventral cord
Only in cervical cord
Controls voluntary movements of the neck

34
Q

What does the corticospinal tract have connections with?

A

Monosynaptic connections with motor neurons of thumb and digits only
- other muscles motor actions mediated by CST acting on spinal interneurons

35
Q

What does damage to the corticospinal tract in the spinal cord cause?

A

Loss of control of hand and fingers

Posture/locomotion and gait not lost

36
Q

What is the extrapyramidal system?

A

Other descending tracts mediating motor functions of posture, locomotion and gait
- originate from groups of cell bodies in the brainstem

37
Q

What are the main components of the extrapyramidal system?

A
  • lateral vestibulospinal tract

- reticulospinal tracts

38
Q

What is the function of the lateral vestibulospinal tract?

A

Controls posture and balance

- tonically active during upright posture

39
Q

What is the pathway of the lateral vestibulospinal tract?

A
  • originates in the vestibular nuclei in upper medulla/lower pons
  • projects ipsilaterally to antigravity muscles
40
Q

What is the function of the reticulospinal tract?

A
  • general arousal of spinal cord
  • autonomical control driving sympathetic preganglionic neurons
  • drive to respiration via phrenic nerve
41
Q

What is the pathway of the reticulospinal tract?

A

Arises in the reticular formation of the pons and medulla

- projects bilaterally down spinal cord

42
Q

What is the function of the rubrospinal cord?

A

Carries cerebellar commands to the spinal cord

43
Q

What is the pathway of the rubrospinal cord?

A

Orign in the red nucleus of the brainstem

Receives main input from the cerebellum

44
Q

What is different about the rubrospinal tract in males?

A

It is vestigial - atrophied, remnant left

45
Q

What is the red nucelus?

A
  • large nucleus in midbrain

- gives rise to rubrospinal tract and large ascending projection to motor thalamus

46
Q

What are the minor extrapyramidal pathways?

A
  • tectospinal tract

- medial vestibulospinal tract

47
Q

What is the function of the tectospinal tract?

A

Coordinates voluntary head and eye movements

- activates reflex movements of the head in response to visual and auditory stimuli

48
Q

What is the pathway of the tectospinal tract?

A

Originates in the superior colliculus

  • projects to the contralateral cervical spinal cord
  • terminates in rexed laminae VI, VII, VIII
49
Q

What is the function of the superior colliculus?

A
  • also called the optic tectum

- receives afferents from the retina

50
Q

What is the function of the medial vestibulospinal tract?

A

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
Q

Which upper motor neurons act directly on lower motor neurons in the cord?

A

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
Q

What is spasticity?

A

Abnormally increased muscle tone

  • muscles have increased tendon reflexes
  • characteristsic of UMN lesion
53
Q

What is an example of an UMN lesion?

A

Damage to motor cortex or any descending tract

54
Q

What is clonus?

A

Series of jerky contractions of a particular muscle following sudden stretching of it

55
Q

What is hyper-reflexia?

A

Abnormally/pathologically brisk tendon reflex seen in one or more muscles

56
Q

What are some severe signs of motor system damage?

A

Decorticate and decerebate posturing

57
Q

What are the features of decorticate posturing?

A

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
Q

What does decorticate posture indicate?

A

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
Q

What are the features of decerebrate posturing?

A 
Arms adducted and extended
Wrists pronated 
Fingers flexed
Legs may be internally rotated and stiffly extended 
Feet may be plantar flexed
60
Q

What would decerebate posturing indicate?

A

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
Q

How can vestibulospinal tract disinhibition cause decerebrate posture?

A

Normally vestibulospinal tract is under tonic inhibition by corticobulbospinal tract and red nucleus
- red nucleus damage by severe midbrain injury = decerebrate posturing

62
Q

What does a discrete acute lesion lead to?

A

Initial paralysis
Followed by variable degree of recovery
During recovering - weakness, clumsiness, fatigue of movements

63
Q

What is plasticity in the cortex?

A

Allows recovery

After lesion muscles may be driven by cells from a different part of the cortex as the homunculus has changed

64
Q

What do larger lesions lead to?

A

Slower recovery
Permanent loss of certain movement
Increased weakness, clumsiness and fatigue

65
Q

What do small lesions lead to?

A

Good recovery of motor skills

Motor weakness and quick fatigue always present

66
Q

What is hemiplegic dystonia?

A

Persisting spasticity following motor cortex lesion
Combined with motor weakness
Persistent flexion of arms and extension of legs

67
Q

What is the clasp knife reflex characteristic of?

A

Chronic cerebral motor lesions

68
Q

What is spinal shock?

A

Condition which occurs after an acute damage to the cord including descending tract damage

69
Q

What are the acute effects of spinal shock?

A

Paralysis/paresis
Reduced reflex responses in all muscles below injury region
If severe - all reflexes below lesion level are inactive

70
Q

What are the chronic effects of spinal shock?

A 
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
Q

What is the difference between an UMN lesion and a LMN lesion?

A

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
Q

In spinal injury which tracts are responsible for which symptoms?

A

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

BB2 (31 decks)

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