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

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

= 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

= 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

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

TASK 1 - CORE MOTOR SYSTEMS Flashcards by Emma Trinker

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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)

How well did you know this?

Not at all

Perfectly

ready-set-go idea

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

motor neurones

= final neural elements of motor system

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

motor neurones

- gamma motor neurones

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

How well did you know this?

Not at all

Perfectly

alpha-gamma co-activation

alpha neurone activation
extrafusal fibres contracted + intrafusal don’t
gamma neurone activation
both contracted

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

proprioceptive spinal reflex

= reflex due to internal trigger

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

How well did you know this?

Not at all

Perfectly

exteroceptive spinal reflex

= reflex due to external triggers (pain, itch)

How well did you know this?

Not at all

Perfectly

rhythmic/automatic movements

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

descending spinal tracts

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
ventromedial pathways
- use sensory info about balance, body position, visual environment to maintain balance and posture
- proximal muscles
- brainstem control

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

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

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

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

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

pyramidal tract

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

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

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

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)

M1 | - somatotopic organisation

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

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

high level | - non-primary motor areas

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

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

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

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

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

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

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)