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Functional Neuroanatomy > TASK 1 - CORE MOTOR SYSTEMS > Flashcards

TASK 1 - CORE MOTOR SYSTEMS Flashcards

1
Q

hierarchical organisation of motor control

- high level

A

= association areas (+ basal ganglia)
= M1, PMA, SMA, PFC, PPC
- STRATEGY/PLANNING: figure out goal of movement + best strategy to get there
- get sensory info from cortex about where body is in space (mental image of where I am in relation to environment)
- alternatives are filtered (based largely on experience) through basal ganglia

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2
Q

hierarchical organisation

- middle level

A

= motor cortex (M1) + cerebellum/ (brainstem structures with assistance of cerebellum + basal ganglia)

  • TACTICS: concerned with the sequences of muscle contractions to smoothly + accurately achieve the strategic goal
  • based on memory of sensory info from past movements
  • translate action goals into movement instructions to lower level
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3
Q

hierarchical organisation

- low level

A

= brain stem + spinal cord

  • EXECUTION: activation of neurones that generate goal directed movements + necessary adjustment of posture
  • motor neurones & interneurones
  • sensory feedback is used to maintain posture, muscle length + tension before/after each voluntary movement (= adjustments)
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4
Q

ready-set-go idea

A 
READY = depends on activity of parietal & PFC
SET = depends on SMA & PMA 
GO = M1 (when movement is initiated PMA & SMA cease to fire)
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5
Q

low level

- muscles

A
  • often organised in antagonist pairs –> flex or extend
  • activated by motor neurones
  • extrafusal fibres: outer muscles
  • intrfusal fibres: measurement device for contraction; inside
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6
Q

motor neurones

A

= final neural elements of motor system

- originate in spinal cord –> exit through ventral root –> terminate in muscle fibres

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7
Q

motor neurones

- alpha motor neurones

A

= innervate muscle fibres + provide physical basis for translating nerve signals into mechanical action

  • input: muscle spindle –> DORSAL root –> motor neuron in spinal cord
  • muscle spindles (= inform them about how stretched the muscle is)
  • output: spinal cord –> VENTRAL root –> muscle fibres –> release acetylcholine (ACh) –> contraction
  • can be/has to be excitatory + inhibitory at same time –> overcome stretch reflex + permit voluntary movement
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8
Q

motor neurones

- gamma motor neurones

A

= sense + regulate length of muscle fibres (part of proprioceptive system)

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9
Q

alpha-gamma co-activation

A
  1. alpha neurone activation
  2. extrafusal fibres contracted + intrafusal don’t
  3. gamma neurone activation
  4. both contracted
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10
Q

spinal interneurones

A

= integration of sensory feedback with motor commands resulting in voluntary movement

  • lie within spinal cord
  • innervate motor neurones
  • input: descending motor fibres that originate from cortex (signals either excitatory or inhibitory) + afferent sensory nerves
  • output: motor neurons
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11
Q

reflex

A

= most simple forms of movements; stereotypical movement patterns controlled from brain stem + spinal cord (low level)

  • fast, smallest circuits, small number of neurones involved
  • can be purely spinal
  • innate
  • fixed stimulus-response coupling
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12
Q

proprioceptive spinal reflex

A

= reflex due to internal trigger

  • e.g.: stretch reflex
  • posture maintenance
  • compensation for motor output variability
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13
Q

exteroceptive spinal reflex

A

= reflex due to external triggers (pain, itch)

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14
Q

rhythmic/automatic movements

A

= mediated by central pattern generators (= neural circuits with intrinsic activity) in spinal cord + brain stem (low level)

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15
Q

voluntary movement

A

= controlled by forebrain (high level)

  • slow(er)
  • involvement of cortex/forebrain
  • late in development
  • flexible stimulus-response coupling
  • experience of intention + agency matter
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16
Q

descending spinal tracts

A
  1. lateral pathways
    - voluntary movement of distal muscles
    - direct cortical control
    - transmission of commands for skilled movement (high level)
    - corrections of motor patterns generated by spinal cord
  2. ventromedial pathways
    - use sensory info about balance, body position, visual environment to maintain balance and posture
    - proximal muscles
    - brainstem control
17
Q
  1. lateral pathways

- corticospinal tract

A

= from cortex to spinal cord
- longest & largest in CNS
- origin: 2/3 in motor cortex (areas 4 & 6 of frontal lobes), 1/3 from somatosensory areas (regulate flow of somatosensory info to the brain)
- cortex –> through internal capsule (= bridge between telencephalon + hypothalamus) –> through cerebral peduncle (= collection of axons in midbrain) –> through pons –> collect to form tract in medulla –> forms bulge (= medullary pyramid) –> crosses at junction to spinal cord (contralateral control) –> axons collect in lateral column of SC
- termination: dorsolateral region of ventral (to the belly) horns & intermediate grey matter
= control distal muscles

18
Q
  1. lateral pathways

- rubrospinal tract

A

= from red nucleus to spinal cord

  • smaller component, indirect
  • origin: red nucleus of midbrain; most input to red nucleus from motor cortex
  • -> almost immediately decussates/crosses in pons –> joins corticospinal tract in lateral column of SC
  • contributions in humans reduced –> most functions subsumed by corticospinal tract
  • can compensate lesion of corticospinal –> gaining larger role when corticospinal lesioned
19
Q
  1. ventromedial pathways

- vestibulospinal tract

A

= from vestibular nuclei to spinal cord

  • keep head balanced on shoulders as body moves + turn in response to stimuli
  • generation pf tonic activation in antigravity muscles
  • origin: vestibular nuclei of medulla (= relay sensory info from vestibular labyrinth in inner ear)
    a) bilaterally down spinal cord: activates cervical spinal circuits that control neck + back muscles –> guide head movement
    b) ipsilaterally as far down as lumbar spinal cord: maintain posture by influencing motor neurones of the legs
20
Q
  1. ventromedial pathways

- tectospinal tract

A

= from tectum (superior colliculi) to spinal cord

  • keep head balanced + turn in response to stimuli
  • coordination of head + eye movements
  • origin: superior colliculus of midbrain (input from retina + projections from visual cortex)
  • creates map of environment from input –> stimulation of one point on this map leads to an orienting response
21
Q
  1. ventromedial pathways

- reticulospinal tract

A
  • origin: reticular formation (input from many sources, many different functions)
  • activation of spinal motor programs for stereotypic movements
  • control of upright body posture
    1. pontine reticulospinal tract = from medial reticular formation (pons) to spinal cord
  • enhances antigravity reflexes of spinal cord = helps maintain standing posture by resisting effects of gravity (maintains muscle length)
    2. medullary reticulospinal tract = from lateral reticular formation (medulla) to spinal cord
  • opposite = frees antigravity muscles from reflex control
  • -> activity of both controlled by descending signals from cortex
22
Q

pyramidal tract

A

= corticobulbar (= to brain stem motor nuclei for face, head, neck) + corticospinal tract
- decussate/cross at medullary pyramid

23
Q

middle level

- cerebellum

A
  • input: project to cerebellar cortex
  • output: brainstem nuclei & cortex via thalamus
  • ipsilateral organisation
    1. vestibulocerebellum = oldest part; to brainstem vestibular nuclei
    a. balance & coordination of eye movement with body movement
    2. spinocerebellum = middle region; input from vision, auditory + proprioceptive system and output to descending systems (extrapyramidal)
    a. motor execution & balance
    3. neocerebellum = newest part; input from parietal & PFC, output to motor areas
    a. motor planning
24
Q

middle level

- basal ganglia

A

= collection of five nuclei: striatum (caudate nucleus + putamen), globus pallidus, subthalamic nucleus, substantia nigra

  • input: via striatum
  • output: globus pallidus to thalamus (to motor, frontal regions) & part of the substantia nigra
  • initiation
25
Q

high/middle level

- primary motor cortex (M1)

A

= area 4

  • most posterior of frontal lobe; pre-central gyrus (= motor strip)
  • somatotopic organisation
  • strongest synaptic connection with motor neurones (lowest threshold for initiation of movement when stimulated)
  • origin of pathways: Betz cells (pyramidal cells in layer 5)
  • input: cortical areas, cerebellum through thalamus
  • output: directly to spinal cord + brain stem areas involved in sensorimotor processing
    a) rostral neurons: terminate on spinal interneurons
    b) caudal neurons: terminate directly on alpha neurons
  • plasticity: through learning reorganised (= cells switch from on type of movement to another)
26
Q

M1

- somatotopic organisation

A

= motor homunculus

- cortical magnification: importance of effector for movement, level of control required determines size

27
Q

M1

- population coding

A

= neurones encode force & direction of movement by means of population coding

  • direction of movement depends on the average of votes
    1. activity of each cell represents a direction vector (preferred direction; its own vote)
    2. length of vector shows how active that cell was during movement (how strongly promotes its vote)
    3. population vector = averaging vectors of different directions/neurones (averaging all votes of population and see which direction wins)
  • the larger the population of neurones, the finer the possible control
28
Q

high level

- non-primary motor areas

A

= all areas in frontal lobe that can influence motor output at the level of the M1 + spinal cord

29
Q

high level

- secondary motor areas

A

= premotor + supplementary motor area = area 6

  • each has own somatotopic map
  • translation of what actions are desired (higher levels) into how the actions will be carried out (lower levels)
  • general instructions from PFC –> programming of specific patterns of movement
  • planning of movements yet to come (specialised for skilled, voluntary movement)
  • output: M1
30
Q

secondary motor areas

- supplementary motor area

A

= SMA

  • medial
  • strong connections with medial frontal cortex
  • -> internally/memory guided personal preferences and goals
  • heavily interconnected with M1
  • stronger connections with PFC
  • -> more difficult
  • sends axons to directly innervate distal motor units
31
Q

secondary motor areas

- premotor area

A

= PMA

  • lateral
  • strong connections with parietal lobe
  • -> external visually/sensory-guided actions
  • primarily connects with reticulospinal neurons innervating proximal motor units
  • rostral PMd: strong connections with PFC
  • -> selects responses based on arbitrary spatial cues
  • caudal PMd: strong connections with M1
  • -> generation of movements
  • PMv: dual role = execution + observation of object-related hand movements (e.g. pre-shaping)
  • -> parieto-frontal circuit: anterior intraparietal area (AIP) & PMv
  • responsible for transformation of visual representation of geometric properties to motor commands
32
Q

high level

- posterior parietal cortex

A
  • mental body image = current position of body in space; representation of space
  • sensory integration
  • directs behaviour by providing spatial information
  • area 5 = somatosensory cortex; input from S1
  • -> provides representation of body and how it is situated in environment
  • area 7 = input from higher order visual areas
  • largely connected to PFC
  • damage: deficits in perception and memory of spatial relationships, accurate reaching
33
Q

high level

- prefrontal cortex

A

= decisions about what actions to take + their likely outcome (evaluation of external stimuli as perceived by parietal cortex)

  • Broca’s area + insular cortex: production of speech movements
  • area 8: frontal eye fields (control of eye movements)
  • ACC: selection and control of actions, evaluating effort/costs required to produce movements
  • PFC + PPC: encode what actions are desired + send axons to area 6
34
Q

brain-machine interface

A
  1. implant microelectrode
  2. analyse spiking patterns = know how they encode movement
  3. use decoded activity to move a cursor on screen
    - cells in M1, PMA, SMA & parietal cortex
    - motor commands (not motor feedback YET)

Functional Neuroanatomy (5 decks)

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