Lecture 4: Motor Control pt. I Flashcards
what is motor control
process of initiating, directing, and grading purposeful volitional movement
responding actions to environmental stimuli (most of the nervous system components for sensory and integrative function)
top down vs bottom up motor control
top down = do not need external stimuli
bottom up = respond to external stimuli
CPGs = still work w/o CNS control
how do reflexes work with motor control
stimulus is sent to the CNS
instead of getting interpreted with cognition, CNS directly interacts with motor neurons causes immediate action
describe the hierarchial organization of motor control
4 levels
all levels above level 1 = UMN system
neurons in level 1 = LMN system (SC)
2 side loops = basal nuclei and cerebellum
what are the 4 levels of hierarchy of motor control
level 1 = SC
level 2 = brain stem
level 3 = motor cortex
level 4 = association cortex
what is functional segregation related to motor control
various functional regions in nervous system for motor control
what are the components of level 4 of motor control hierarchy (multimodal association cortex) (6)
cingulate motor area (part of limbic system)
posterior parietal cortex (Brodmann 5, 7)
Frontal eye field (Brodmann 8)
Language areas
-Broca’s (Brodmann 44,45)
-Wernickes (Brodmann 22)
prefrontal cortex for functional execution
what is the function of the cingulate motor area in motor control
reciprocal projections with many structures that have different functions/send different information
what are the reciprocal projections of the cingulate motor area and their function
L dorsolateral prefrontal cortex = motor planning and execution (working memory)
oribitofronal cortex = collecting/summarizing results of motor programs
cingulate motor area = calculating reward of motor program
describe how the cingulate motor area calculates “reward” of a motor program performed
emotion related behaviors; motivation vs aversion
making the decision of if it is worth doing something or not
alternate motor control theory = invest and reward
what are the functions of the posterior parietal cortex in motor control related to vision
Dorsal visual pathways
- process context and spatial rep of objects (where)
-visuomotor transformations = how to respond to visual stimuli (integration of perception to action)
specialized area for reach and grasp (lateralized to L hemisphere)
- process object size
-orientation
-hand matching
saccadic eye movements = hand eye coordination
functions of the posterior parietal cortex in regard to motor control
functions are lateralized
R = bilateral attention scanning and spatial cognition
- L side hemineglect occurs when R side is damaged; ischemic vs hemorrhagic stroke
L = praxis and language
- L side damaged = apraxia
what are the components of level 3 motor control
unimodal association cortex made up of:
-supplemental motor area - Brodmann 6
-premotor cortex - Brodmann 6 dorsal/ventral
primary motor cortex (M1) - Brodmann 4
where is the SMA
medial frontal lobe
anterior to M1
has a gross topographic distribution
What areas of the brain does SMA “talk to” in regard to motor control; what guides its function?
directly “talks” with cingulate motor area
performance is guided by internal cues - OPEN LOOP/top down; no sensory input required
coordinates sequential tasks
what areas of the brain are activated in the brain when performing simple motions, complex motions, and imagery of complex motions respectively
simple motion = unilateral M1/S1 activation
complex motion = unilateral M1/S1 and bilateral SMA
imagery of complex motion = bilateral SMA
functions of SMA in motor control
coordination of bimanual movements during complex movements
active during motor imagery (mental rehearsal of bimanual and sequential tasks)
locations of primary motor area
dorsal to ventral along brodmann area 6
functions of premotor cortex in motor control
- signals the preparation for movement - via motor set neurons
- signals correct and incorrect actions
- signals various sensory aspects associated with motor actions - via mirror neurons
- distinguishes the same movement based on behavioral context (i.e. picking up full vs empty cup)
- relies on external sensory input for movement (conext) - CLOSED LOOP
- motor imagery WITH external stimuli; bottom up
what are mirror neurons
where perception and action integrates
NOT in occipital lobe
sensorimotor pathway of mirror neurons and it’s function
somatic motor
different neuron for different movement patterns
- strictly congruent = only respond to 1 stimuli
- broadly congruent = respond to multiple
function = understanding intention of the movement (learning)
emotion pathway of mirror neurons
self and social cognition
recognizing cultural conflict
individualism vs collectivism
helps humans understand one another
what happens if the sensorimotor and emotion pathways of mirror neurons are not integrated in daily life
autism spectrum disorder
functional impairment of the association cortex results in what
apraxia
apraxia definition
cant perform skilled or learned movements with intact sensory or motor system (loss of mirror neiron connections)
ideational apraxia; it is a loss of what
know the tools but cant use them
loss of action sequencing
ideomotor apraxia
know how to perform an activity but cant perform the actual activity
limb kinetic apraxia
unable to make precise, independent but coordinated movx ements
apraxia is mainly related to what 2 parts of the brain
left premotor (6) and posterior parietal cortex (5)
compromised mirror neurons
classic model of the homunculus of M1
lower limb to tongue in an inverted representation
updated model of the homunculus of M1 as well as the clinical significance of this new model
3 symmetric concentric topographic representation
spaced by 3 cognitive control regions
clinical significance:
- poor foot, hand, and tongue fine motor control recovery
- all UMN neurons control patterns of motion, not contraction of a single mm
describe the motor neuron distribution in M1
chimeric distribution of M1
gross order with gradient distribution (overlap)
not like S1 which is still strictly represented in homunculus
describe the neuronal firing in M1
fire 5-100msec before onset of movement
fastest region when stimulated = existing mechanisms for direct LMN control
M1 neurons encode what info
force of movement
extent of movement
speed of movement
direction of movement
what defines the intention of the movement in M1
pyramidal cells
columnar of neurons oversee specific behavior
describe the S1 homunculus
strictly follows topographic representation of body
function of S1 in motor control
direct projection to M1
adjusts movement constantly
What are the components of the corticobulbar and corticospinal tracts
monosynaptic M1 neurons
disynaptic neurons
**S1 does NOT contribute much to human corticobulbar and corticospinal tracts
describe monosynaptic M1 neurons and their function
develop postnatally
located caudal to M1, anterior bank of central sulcus
directly synapse with LMN for fine motor control
describe disynaptic neurons and their function
developed prenatally, through interneurons to LMN
located in:
-rostral M1
-dorsal and ventral PM/SMA (brodmann 6)
-2 from cingulate gyrus
-posterior parietal lobe (Brodmann 5)
describe the path for the descending cortical tracts for motor control
through the posterior limb of the internal capsule
rotates while descending
gross topography maintained above the pons
somatotopy = face to LE from anterior to posterior; rotation from medial to lateral
where are the nuclei of the corticobulbar tract and their function with motor control
motor nuclei in brainstem
6 nuclei = w/o CN III/IV/VI for neck/head mm
brainstem motor control function = red/reticular/vestibular nuclei; generally inhibition
describe the path for the corticospinal tract
travels all SC levels
has collateral terminals for brainstem motor nuclei
where are the decussations for the corticospinal tract and where do the fibers continue afterward
70-90% decussate in pyramid (caudal medulla) = for contralateral body control
these tracts descend in the lateral funiculus and form the lateral corticospinal tract for extremity flexors and fine motor control
the rest do not decussate and continue ipsilaterally
some go to anterior funiculus and form the medial corticospinal tract for bilateral trunk mm and postureal control
the rest go to the ipsilateral funiculus to form the ipsilateral lateral corticospinal tract for extremity flexors and fine motor control
level 2 of motor control is made up of what areas of the brain and what are their associated tracts
brainstem
midbrain = rubrospinal tract
pons = pontine reticulospinal tract and vestibulospinal tract (lateral and medial)
medulla = medullary reticulospinal tract
function of rubrospinal tract in motor control and general pathway
fine motor control; flexors of UE and trunk
decussates in midbrain
descends into lateral funiculus of SC
learning a new skill goes through what circuitry and involved what fibers
through the red nucleus-inferior olivary nucleus-cerebellum circuitry
climbing fibers are involved
general functions/path of reticular nuclei in motor control
generally bilateral projections through anterior funiculus
pontine reticulospinal tract = all spinal levels, controls extensors (posterior control)
medullary reticulospinal tract = all splinal levels, controls flexors (anterior control)
paths of the vestibulospinal tracts and what they control
lateral vestibulospinal tract = ipsilateral anterior funiculus for proximal extremity extensors
medial vestibulospinal tract = bilateral anterior funiculus for neck/upper trink extensors
which tracts descend the whole SC
pontine reticulospinal tract
lateral vestibulospinal tract
medullary reticulospinal tract
how far does the medial vestibulospinal tract descend
into C/S (neck)
how far does the rubrospinal tract descend
to UE
what is decerebrate posture
** without cerebral peduncle; lesion BELOW RED NUCLEUS
no functional rubrospinal tract and corticospinal tract
no flexor tones
no inhibition of level 2 motor control system
UE and LE both in EXTENSION synergies
what is decorticate postire
** without cerebral cortex; lesion ABOVE RED NUCLEUS
upper limb flexors activated by rubrospinal tract without cerebral cortex inhibition
UE in FLEXION synergies
LE in EXTENSION synergies
why do both decerebrate and decorticate postires have extension synergies in LEs
in both cases the vestibulospinal tracts are active
BLEs are in extension
