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Upper MN Flashcards

(57 cards)

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1
Q

Describe medial motor neuron and interneuron groups

A

Receive descending input from pathways that originate mainly in the brainstem

Course through the anterior-medial white matter of the spinal cord and terminate bilaterally

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2
Q

Describe the lateral motor neuron and interneuron groups

A

Receive major descending projection from the contralateral motor cortex via the main lateral division of the corticospinal tract which runs in the lateral white matter of the Spinal cord

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3
Q

Where are upper MN in the cerebral cortex?

A

Posterior frontal lobe

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4
Q

Upper MN do what?

A

Mediate planning and initiation of complex temporal sequences of voluntary movements

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5
Q

Upper MN are modulated by?

A

Basal ganglia
Cerebellum (via thalamus)
Sensory inputs from the parietal regions

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6
Q

Motor cortex refers to?

A

The primary motor cortex (M1)

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7
Q

The primary motor cortex is located where?

A

Anterior bank of the central sulcus

Paramedian lobule

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8
Q

The primary motor cortex can be distinguished from the premotor regions by?

A

Cytoarchitecture (brodmann’s area 4)
Low electrical threshold for eliciting movements due to direct connections to brainstem and spinal cord alpha motor neurons

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9
Q

Describe giant pyramidal neurons

A

Located in layer 5 (Betz cells)

Represent 5% of the total upper motor neurons of M1

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10
Q

Giant pyramidal neurons project to?

A

Via the corticospinal tract (to spinal cord controlling movements from the neck down) and corticobulbar tracts (to brainstem controlling face movements)

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11
Q

Non-Betz pyramidal neurons?

A

Remaining upper motor neurons in layer 5 that are found in M1 and the premotor corticies

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12
Q

Neurons in the motor and premotor coritices give rise to axons that? Where from there?

A

Travel through the internal capsule and coalesce on the ventral surface of the midbrain within the cerebral peduncle

Continue through the pons and come to lie on the ventral surface of the medulla giving rise to the medullary pyramids

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13
Q

Collaterals from the motor and premotor corticies?

A

As axons course through the brainstem, corticobulbar axons give rise to collaterals that innervate brainstem targets (cranial nerve nuclei, reticular formation, and red nuclei)

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14
Q

Most of the corticospinal tract nerves cross hwre?

A

In the caudal part of the medulla to form the lateral CST in the spinal cord (90%)

Those that do not cross form the ventral CS tract that terminates bilaterally in the lower motor neurons innervating proximal muscles

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15
Q

Axons that form the ventral CS tract project where?

A

Some directly to alpha motor neurons like in the hand but most contact interneuronal pools

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16
Q

Some components of the cortico-fugal projections from the layer 5 of the parietal regions (somatosensory) terminate?

What do these do?

A

In the interneurons near the sensory trigeminal and dorsal column nuclei in brainstem and in the dorsal horn in the spinal cord

Modulate transmission of proprioceptive and mechanosensory signals relevant to monitoring body movements

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17
Q

Describe the functional organization of M1

A

Post central gyrus

Fine motor control of face and hands are represented by a greater area of motor cortex than is the musculature requiring less precise motor control

Also somatotropically orgnaized

Contralteral to body intervated

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18
Q

Describe pathway somatotropy

A

Keep somtatotropic organiztion down to targets

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19
Q

Axons from the face are located?

A

In the genu of the internal capsule

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20
Q

Axons for motor commands from the arm region are located where relativel to the trunk and leg?

A

Posteriorly

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21
Q

Somatropic arrangement for the corticofugal pathways are seen where?

A

Cerebral peduncle
Pons
Medulla
Spinal cord

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22
Q

Individiual pryamidal tract axons termiante?

A

On sets of spinal motor neurons that innervate different muscles

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23
Q

Describe topographic representation of movement in M1

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A

Organized around different categories of motor behaviors

Seen in premotor areas as well

24
Q

Lower MN damage in the face affects all muscles…

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A

Ipsilateral to the side of the lesion

Superior and inferior facial muscles

25
Upper MN damage in the face tends to spare?
The forehead Mostly affects the inferior portion of the CONTRALATERAL face
26
Why does upper MN damage affect the contralteral face? Why spare forehead?
Corticobulbar projections from M1 are directed to the lateral cell columns in the contralateral facial motor nucleus Dorsal cell columns that innervate the superior facial muscles are governed by bilateral premotor areas in M! and anterior cingulate gyrus
27
Why is injury to upper MN common?
Large amount of cortex occupied by motor areas Also pathways extend all the way from cerebral cortex down to the lower end of the spinal cord
28
Initial manifestation of upper MN damage?
Most severe in arms and legs Hypotonia (spinal shock) due to decrease in spinal activity by decrease in spinal activity by the interruption of descending commands
29
Trunk muscle control in upper MN syndrome?
Usually preserved because of bilateral projections of the corticospinal pathway to local circuits that control midline musculature
30
Several days after upper MN damage?
Spinal cord circuits regain much of their function Thereafter Babinski sign is present
31
What is babinski sign?
Stroking foot should evoke flexion of big toe Following damage to the descending upper MN stimulates extension of big toe and fanning of other toes Occurs in human infants before maturation of the corticospinal pathway
32
What is spasticity?
Increased muscle tone and hyperactive stretch reflexes
33
Spasticity is prominent with?
With lesions to the cortex or internal capsule Caused by removal of inhibitory influences from the cortex
34
Extensive upper motor neuron lesions can be accomanpied by?
Rigidity of the extensor muscles of teh leg and flexor muscles of the arm (decerebrate rigitidy) Due to influence from the remnant vesticular n and reticular formation
35
What is clonus?
Oscillatory motor response due to muscle stretching Consequence of hyperreflexivity (movement doesn't stop)
36
Loss of ability to perform fine movements?
Lesion involves descending pathways that control lower MN to the upper limbs
37
Describe the premotor regions
Mosaic of interconnected frontal lobe areas that lie rostral to M1 and contribute to motor function
38
List premotor regions
Lateral premotor dorsal and ventral areas (BA 6l, 44 and 45), supplementary motor area (BA 6m) and cingulate motor regions (BA 23 and 24).
39
Premotor regions receive multisensory inputs from?
Parietal and prefrontal region
40
Premotor regions influence?
Motor behavior indirectly by modulating M1 and with direct projections via the CST and the corticobulbar tracts terminating in the spinal and brainstem interneuronal pools
41
Function of premotor dorsal region?
Associated with selection of appropriate movements before they occur (motor planning) These neurons encode the intention to perform a movement
42
Supplementary motor region is involved in?
Coordination fo bimanual movements
43
Cingulate motor regions are associated with>
Modulation of emotionally triggered movements
44
Ventral premotor cortex is made up of?
Inferior portion of the precentral gyrus Broca's areas
45
What are mirror neurons?
In the ventral premotor cortex Active during the execution of skilled goal oriented actions and discharge at the same rate during observation of the same movement performed by others Imitation and motor learning
46
Describe the vestibulo-spinal pathway
Remember that these are for balance control through the VSR and VCR
47
Describe neurons of the reticular formation?
Scattered among axon bundles that course through the medial portion of the midbrain, pons, and medulla.
48
Reticular formation is found?
In the core region of the brainstem or the brianstem tegmentum
49
Diffuse fibers in the tegmentum are known as?
Reticular formation
50
Describe the function of the reticulo-spinal pathways
Involved in temporal and spatial coordination of limb and trunk movements
51
Reticulo-spinal pathways terminate?
Medial parts of the spinal grey matter Like those from the vestibular nuclei
52
How is anticipatory body posture maintained?
Cued movement of the arm-hand is accomopanied by significant increase in proximal musculature that occurs before contraction of corresponding upper limb muscles
53
What is feedforward mechanism?
Predicts the resulting disturbance in body stability and generates an appropriate stabilizing response
54
Neurons in the motor cortex that supply the lateral part of the ventral horn do what?
Initiate movements of the distal limbs and also terminate on neurons in the reticular formation to mediate postural adjustments to support that movement.
55
Reticulospinal pathway terminates?
In the more medial parts of the ventral horn wehre the lower MN that innervate axial and proximal muscles are located
56
Motor corticies can influence the activity of spinal cord neurons via?
Direct and indirect routes
57
Tectospinal tract is from where and does what?
From superior colliculi and terminates int eh cervical spinal cord Controls axial muscles of the neck (orienting movements of the head) Mostly indirect since major output from superior colliculs is to the reticular formation and from there to the SC

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