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Neuroscience > Week 4 - Upper Motor Neurons and Cortical Control of Movement > Flashcards

Week 4 - Upper Motor Neurons and Cortical Control of Movement Flashcards

1
Q

what are 3 tasks that must be accomplished by the motor system for proper motor control?

A
  1. produce accurately timed commands to many muscle groups
  2. take into account current position of body and distribution of body mass (postural adjustments)
  3. take into account and compensate for physical characteristics of body and muscle
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2
Q

how is the motor system organized and segregated?

A

hierarchially organized and functionally segregated

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3
Q

what are the main motor structures in the CNS, from highest to lowest? what are the highest and lowest levels most concerned with, respectively?

A 
association cortex - complex planning and selection
cortical motor areas
basal ganglia
cerebellum
spinal cord - most autonomic behaviors
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4
Q

are the descending motor pathways from cerebral cortex or brainstem to LMN in medial ventral horns unilateral or bilateral? what do they do?

A

CC: unilateral (via lateral white matter of spinal cord); for distal limb muscles (skilled movements); direct terminations
BS: bilateral (via anterior-medial white matter of spinal cord); for axial and proximal limb muscles (posture and balance); indirect terminations

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5
Q

hwo do the local circuit neurons supplying medial and lateral regions of ventral horn differ?

A

long distance: medial intermediate gray, to axial and proximal limbs (posture, so 2 interneurons exit at every level, one to each side)
short distance: lateral intermediate gray, to distal limbs (fine movements, so only travel down a little way but give off many interneurons at specific levels)

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6
Q

what are direct/indirect terminations on ventral horn motoneurons regulated by?

A

developmentally regulated; differences relate to dexterity between species and infants/young children

  • terminations aren’t yet made in youth, and gone if UMN injury
  • amt of fine control also differs between species
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7
Q

what are the 4 types of indirect descending pathway?

A

projections to a midbrain or brain stem center, then to spinal cord; for gross movement and posture

  1. cortico-colliculo-spinal (tecto-spinal)
  2. cortico-rubro-spinal
  3. cortico-reticulo-spinal
  4. cortico-vestibulo-spinal
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8
Q

what are the 2 types of direct descending pathway?

A

connections from large pyramidal cells in layers III and V to ventral spinal cord

  1. lateral cortico-spinal
  2. medial cortico-spinal
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9
Q

what does the vestibulospinal tract do? where do they originate?

A

changes gain of axial and proximal limb reflexes

  • facilitates anti-gravity muscles
  • originate in lateral and medial vestibular nuclei
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10
Q

what does the reticulospinal tract do? where does it originate?

A

changes gain of axial and proximal limb reflexes

  • for central pattern generator
  • originates in pontine and medullary reticular formation
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11
Q

what does the colliculospinal (tectospinal) tract do? where does it originate?

A

axial and midline body orientation

-originates in superior colliculus

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12
Q

what does the rubrospinal tract do? where does it originate?

A

some distal control, mainly arm flexion

-originates in red nucleus

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13
Q

where does most direct cortico-motor innervation derive from?

A

primary motor cortex (M1)

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14
Q

what kinds of cells control our motor units?

A

most projections are from giant Betz cells

-Betz are only in motor areas, especially primary motor cortex

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15
Q

where are most motor areas of the cortex found? how many skeletal and ocular motor areas are there?

A

on lateral and medial surfaces

-over 5 skeletal and over 2 ocular motor areas

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16
Q

what defines a cortical motor area?

A
  • projects to motor neurons in the spinal cord (either direct CM projections or indirect via interneurons
  • projects to M1
  • contains Betz cells or equivalent large layer V projection neurons
  • can be stimulated at low thresholds to produce movements of discrete muscles or muscle groups
  • displays changes in activity related to parameters of movement
17
Q

what are association areas and how do they compare to cortical motor areas?

A

prefrontal cortex, posterior parietal cortex, temporal cortex, and pre-supplementary motor cortex
-DON’T meet all definitions for a cortical motor area, but can still participate in regulation of motor function

18
Q

what makes up the premotor cortex?

A

lateral premotor cortex

  • dorsal premotor area
  • ventral premotor area

medial premotor cortex

  • supplementary motor cortex
  • cingulate motor areas
19
Q

what does a lesion to the lateral corticospinal tract do? (pre-op, post-d1, post-d7)

A

testing to grab food
pre-op: can grab and pull w/o problem, in 0.3 seconds
post-d1: it takes over 1 second to figure out where food is and pull it out
post-d7: could improve to 0.8 seconds, but still never at level of pre-op

20
Q

what underlies the recovery of improving reactions in the LCST lesion?

A

local circuit neurons

21
Q

what are methods to study motor cortex?

A
  1. anatomical staining and tracing
  2. microelectrode stimulation of small #s of cells
  3. micro- and macro-electrode recordings
    - spike-triggered averaging
    - spontaneous
  4. lesions
  5. non-invasive imaging
22
Q

what are 2 key features about cortical control of movement?

A
  1. individual muscles are represented in multiple locations (even w/in M1)
  2. individual corticospinal neurons diverge to influence multiple motor neuron pools, thus multiple muscles
23
Q

what does it mean that “individual muscles are represented in multiple locations”?

A
  • general somatotopy exists, but detailed analysis of motor map shows re-representations of individual muscles
  • so outputs from disparate parts of cortical motor areas converge on a common set of motor neurons
24
Q

what does it mean that “individual corticospinal neurons diverge to influence multiple motor neuron pools, thus multiple muscles”?

A

muscles are involved in production of same movement (synergists)
-thus, control of spinal cord motor neurons by cortical motor areas displays both convergence and divergence

25
Q

what have microstimulation studies reported?

A
  • outputs are arranged in columns
  • there are multiple representations of each body part, even w/in a single motor area
  • cells w/ similar targets are not located adjacent to one another (fractured somatotopy)
  • columns of functionally-related neurons are connected by horizontal connections
26
Q

how is epilepsy managed surgically?

A
  1. identify seizure locus (use EEG grid electrodes, imaging, or anatomy/function)
  2. map motor cortex (via direct brain stimulation)
  3. resect “hot” functions (via complex spikes or afterdischarges)
  4. make parallel sub-pial incisions if resection is too risky (preserves motor function)
27
Q

what is the method for spike triggered averaging? what does an increase/decrease in EMG mean?

A
  1. record from a single UMN (#1) and a muscle whose LMN (#2) may be influenced by it
  2. average EMG from 2’s muscle for a brief time after each spike (discharge) of 1
  3. if 1 synapses with 2, there will be a change in EMG
    - increase = excitatory
    - decrease = inhibitory

allows one to establish connectivity maps between 1 cortical motor neuron and multiple muscles it might innervate

28
Q

what does it mean that “individual corticospinal neurons diverge to influence multiple motor neuron pools”?

A

it innervates multiple muscles

  • UMN likely contracts lower MNs of 2-3 “pools” (both agonist and antagonists via inhibitory INs)
  • a given UMN probably synapses w/ ALL the lower MNs w/in a given pool
29
Q

what do cortical motor cells code for?

A
  • muscle activity
  • force
  • direction
30
Q

how do cortical motor cells code for:

  • muscle activity
  • force
A
  • flex forearm by co-regulating agonists, antagonists, alphas, and gammas
  • flex the loaded forearm
  • flex/extend arm in specific direction by individual neurons increasing discharge rate for certain directions more than others
31
Q

what are the muscle and movement representations in primary motor cortex?

A

experiment was to hold cylinder 3 ways, and move it in 8 directions

  • muscle: changes firing properties w/ direction change
  • movement: no change w/ direction

the relationship is very predictable, allowing for neuroprosthetics

32
Q

what are examples of neuroprosthetics?

A
  • control driving cursor with mind

- control robotic arm with mind to feed itself

33
Q

does the motor cortex act alone?

A

no

34
Q

what areas of the brain are involved in

  • simple finger flexion
  • sequential finger movements (performance)
  • mental rehearsal of finger movements
A
  • motor cortex and somatic sensory cortex
  • medial premotor area + above
  • medial premotor area only
35
Q

what are the functional specializations for:

  • primary motor (M1)
  • lateral premotor
  • medial premotor
  • pre-SMA
  • prefrontal
A
  • execution of “simple” movements
  • selection of motor responses based on externally-cued (sensory) inputs
  • executing learned sequences and internally-cued movements
  • learning of sequences
  • decision for action and working memory; monitoring outcomes
36
Q

how well do we function w/o signals provided by afferent inputs?

A

normal subject will bring cursor to target in straight path, even if hand is hidden
-deafferented patient will drift if hand is hidden, but straighter if able to see hand

37
Q

how important is positional/stretch information?

A

if arms are in vibrating holders, and the only visible things are lights on fingers, if the arm vibrates when the hand is in specific areas, it will seem like the arm is stretching so it seems like the fingers are moving

38
Q

clonus and loss of fine voluntary movements signs of a lesion where?

A

UMN

39
Q

decorticate VS decerebrate

A

decorticate: lesion above RN, usually cortex (UMN) or internal capsule
- arms flexed, hands clenched, legs extended, and feet turned inward (b/c disinhibition of rubrospinal tract and loss of corticospinal flexor tone in legs)

decerebrate: lesion below RN, usually brain stem (pontine strokes)
- involuntary extension of arms by sides, head arched back, legs extended
- pt. appears rigid, teeth clenched
- can be unilateral or intermittent

Neuroscience (39 decks)

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