Motor Control Flashcards
What is the main function of the primary motor cortex?
directs movement by controlling muscle contraction
Where is the primary motor cortex locates?
precentral gyrus in the frontal lobe
What does the primary motor cotex spatial map show?
disproportions
Hands and lips have a larger area dedicated to them
What is the influence of a single cortical upper motor neurosn on muscle activity?
individual cortical motor neurons can drive numerous motor neuron pools from a group of different muscles involved in moving a limb toward a desired goal
*organized movement
How are movements generated by the primary motor cortex characteristized?
coordinated and purposfully organized
What are the three key takeaways from neuronla population coding of movement direction?
- much of motor cortex is active for every movement
- activity of each cell represents a singe “vote” for movement direction
- direction of actual movement is deteremined by tally averagibg all the votes of the population
What does a poplulation vector represent?
the movement direction encoded by the simultaneous activity of the entire population of recorded units
What does damage at the C1-7 level cause?
quadrilegia (tetraplegia)
loss of normla function in all four limbs
What does damage at the T1-12 and L1-5 level cause?
paraplegia
loss of normla function in legs
full control and feelikng in the arms and hands
What does damage at the S1-5 level cause?
loss of feeling in the genital arae
Explain a brain-machine interface
a population vector algorithm translates brin waves inot intended movement commands
allows a paralysed person to manipulate objects
What is the result in rats when a motor nerve is cut?
the cortical regions that previously evoked that movment now causes muscle movment somewhere else
*motor map reorganized
What can occur in rats training for a task requiring precise reaching and grasping?
the respresentation of the digits and wrist has epxanded into areas previously associayed with the shoulder and elbow
*younger at the start of training the larger the re mapping
What are the firing patterns of supplementary motor area neurons?
tey response only during a pulling response that was to be followed by a rushing response in a ready set go task
What is the nonprimary motor cortex?
frontal lobe regions adjacent to the primary motor cortex that contribute to motor control and modulate the activity of the primary motor cortex
What is the supplementary motor area?
a region of the nonprimary motor cortex that receives input from the BG and modulates the activity of the primary motor cortex
*internally generates stimuli
What is the premotor cortex?
a region of the nonprimary motor cotex just anterior to the primary motor cortex
*external cues (sensory information)
Where are many mirror neurons found?
ventral portion of the premotor cortex F5
When does a mirror neuron fire the most?
activation is increased most strongly in response to scense of action with clear intention
*movement has a goal - grasping an object vs no object
How doe mirror neurons distinguish between possible intentions?
they response more intensely to the basic biological function of drinking than to cultrally acquired act of cleaning
How are mirror neruons a survival advantage?
understanding the intention of others is fundamental to human social behaviour
What are mirror neurons?
a neuron that is active both when an individual makes a particular movement and when that individual sees another make that same movement
What was found when fMRI’s were done to image disgust?
feeling disgust activated similar parts of the brain when human volunteers experiences the emotion while smelling a disgusting odor or when the smae subjects watched a film clip of someone else digusted
What may overalpping neuron groups represent?
a physical neural mechanism for human empathy that permits understanding the emotions of others
How might underactivation of mirror neurons affect autism?
the pars opercularis region is less actiavtes in children with autism than in controls
contains mirror neurons
deficits in activating brain regions underlying imitation and empathy contribute to the social impairments of autism
What do the lower motor neurons in the medial ventral horn govern?
posture, balance, locomotion, and orienting movements of the head
What do the lower motor neurons in the lateral ventral horn govern?
mediate the expression of skilled voluntary movements of the distal extremities
Where does the lower motor neuron in the medial ventral horn receive descending input from?
pathways that originate in the brainstem -> through anterior white matter of the spinal cord, then termination bilaterally
Where does the lower motor neuron in the lateral ventral horn receive major descending projections from?
the contralateral motor cortex via the main (lateral division) of the corticospinal tract (crosses midline)
- runs in the lateral white matter of the spinal cord
How is the ventral horn somatotopically organized?
in the grey matter
- medial white controls proximal muscles
- lateral controls distal muscles
What is the pathway of the lateral corticospinal tract?
upper motor neurons in the primary cortex sends axon downward to cross over at the pyramidal decussation
the axon then continues downward in the contralateral spinal cord before synapsing on the lower motor neurons in the anterior horn
What is the pathways of the corticospinal tract?
motor cortex -> internal capsule -> midbrain -> pons -> meduallry pyramids -> pyramidal decussation -> lateral column of the spinal cord
What is the somatic organization of the posterior limb of the internal capsule?
leg
trunk
arm
face
(post to ant)
What does the right motor cortex control?
the left side of the body
What is a common way for the corticospinal tract to be damaged?
by stroke -> large pathway
result in contralateral paralysis
recovery can occur but fine motor movements are usually least preserved
What are the possible injury sites for a fall that results in paraplegia?
bilateral medial frontal lobes (leg region)
nerve roots
peripheral nerves
muscles
spinal cord below T10 - likely because only deficits in both left and no weakness anywhere else
What are the possible injury sites for an injury that results in quadriplegia?
bilateral frontal lobes (leg and arm region)
spinal cord (C7-T1) - likely
peripheral nerves
What are the possible injury sites for an injury that results in pure motor hemiparesis? (no sensory deficits)
contralateral spinal tract
- posterior limbs of the internal capsule or ventral pons
* leg, arm, and face axons converge and has not crossed over midline yet
What is the function of the vestibulospinal tract and tectospinal tracts?
To keep the head balanced as our body moves and to turn our heads in response to new sensory stimuli
What is the pathway of the medial vestibulospinal tract?
projects bilaterally down the spinal cord and activated cervical spinal circuits that control the neck and back muscles to guide our head movements
What is the pathway of the lateral vestibulospinal tract?
projects ipsilaterally as far down as the lumbar spinal cord
helps maintain an upright and balanced posture by facilitating extensor motor neurons of the legs
What is the pathway and function of the tectospinal tract?
superior colliculus -> deccussation -> contralateral termination
- orientation response of head and eyes in response to primarily visual stimuli
What is the function of the pontine reticulospinal tract? (medial)
enhances the antigravity reflexed of the spinal cord
- activation facilitated extensors of the lower limbs to help maintain a standing posture by resisting the effects of gravity
What is the function of the medullary reticulospinal tract? (lateral)
liberates the antigravity muscles from reflex control
- opposite of pontine
What is the feedforward mechanism of postural control?
programmes and typically precede the onset of limb movement
What is the feedback mechanism of postural control?
initiates by sensory inputs that detect postural instability
What are the indirect pathways from the motor cortex to the spinal cord?
neurons that supply the lateral ventral horn to initiate distal limb movements also terminate on the neurons in the reticular formation to mediate postural adjustments that support the movement
What occurs with the activation of the motor cortex with inactivation of the reticular formation?
there will be no postural adjustment
* feedforward control
What is the cross-extensor reflex?
reflex in response to pain detected by nociceptors
caused the ipsilateral (pain) flexor muscles to activate
the opposite limb extensor muscles are activated to support the body
What is the cross-extensor reflex an example of?
coordinated movement without commands from the brain
What are central pattern generators (CPG)?
circuits that give rise to rhythmic motor activity
Explain the rhythmic activity in a spinal interneuron
glutamate caused NMDA receptor channels to open - the cell membrane depolarizes, and Ca2+ enters the cell
intracellular rise in Ca2+ causes Ca2+ activated K+ channels to open - K+ leaves hyperpolarizing the membrane
hyperpolarization allows Mg2+ to enter and clog the channel, stopping the flow of Ca2+
causes the K+ channel to close, resetting the membrane potential
What are the primary rhythmic driving force for cyclic behaviours?
spinal interneurons due to their intrinsic pacemaker activity and interconnections
What are the stages of walking?
swinging and stance
How do the stages of walking change when the speed of walking increases?
decreased cycle time by decreasing the time spent in the stance phase
When a cat is trotting, how do the stages of walking change? (LH, LF, RH, RF)
LH and RF are synched
LF and RH are synched
When a cat is pacing, how do the stages of walking change? (LH, LF, RH, RF)
LH and LF synched
RH and RF are synched
When a cat is galloping, how do the stages of walking change? (LH, LF, RH, RF)
LH and RH synched
LF and RF synched
* large decrease in stance phase
With a transection of the spinal cord in a cat, what occurs relative to walking?
remains coordinated reflex response (CPG)
CPG is a critical pre-cursor that excites the descending pathway to get movement without sensory control (doesn’t need top-down control)
* movement is not perfect and does not work well in humans (biped)
Explain the circuit for the CPG of locomotion
neuronal modules for flexion and extension antagonism are composed of excitatory neurons and reciprocally connected inhibitory interneurons
- the received input from excitatory rhythm generator interneurons (reciprocally inhibited)
