TASK 1 - CORE MOTOR SYSTEMS Flashcards Preview

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Flashcards in TASK 1 - CORE MOTOR SYSTEMS Deck (34):
1

hierarchical organisation of motor control
- high level

= 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

2

hierarchical organisation
- middle level

= 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

3

hierarchical organisation
- low level

= 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)

4

ready-set-go idea

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

5

low level
- muscles

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

6

motor neurones

= final neural elements of motor system
- originate in spinal cord --> exit through ventral root --> terminate in muscle fibres

7

motor neurones
- alpha motor neurones

= 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

8

motor neurones
- gamma motor neurones

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

9

alpha-gamma co-activation

1. alpha neurone activation
2. extrafusal fibres contracted + intrafusal don't
3. gamma neurone activation
4. both contracted

10

spinal interneurones

= 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

11

reflex

= 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

12

proprioceptive spinal reflex

= reflex due to internal trigger
- e.g.: stretch reflex
- posture maintenance
- compensation for motor output variability

13

exteroceptive spinal reflex

= reflex due to external triggers (pain, itch)

14

rhythmic/automatic movements

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

15

voluntary movement

= controlled by forebrain (high level)
- slow(er)
- involvement of cortex/forebrain
- late in development
- flexible stimulus-response coupling
- experience of intention + agency matter

16

descending spinal tracts

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

1. lateral pathways
- corticospinal tract

= 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

1. lateral pathways
- rubrospinal tract

= 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

2. ventromedial pathways
- vestibulospinal tract

= 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

2. ventromedial pathways
- tectospinal tract

= 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

2. ventromedial pathways
- reticulospinal tract

- 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

pyramidal tract

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

23

middle level
- cerebellum

- 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

middle level
- basal ganglia

= 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

high/middle level
- primary motor cortex (M1)

= 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

M1
- somatotopic organisation

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

27

M1
- population coding

= 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

high level
- non-primary motor areas

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

29

high level
- secondary motor areas

= 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

secondary motor areas
- supplementary motor area

= 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

secondary motor areas
- premotor area

= 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

high level
- posterior parietal cortex

- 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

high level
- prefrontal cortex

= 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

brain-machine interface

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)