upper motor neurons and cortical control of movement Flashcards
what are the main motor structures in the CNS?
in order of highest to lowest: assoc. cortex, cortical motor areas, basal ganglia, cerebellum, spinal cord
what do the lower level of motor control ( e.g. spinal cord) vs. the higher ( e.g. cortex)
low levels accomplish most of the automatic behaviors, while high levels do more of the complex planning and selection
motor cortex ( upper motor neurons) is involved in what type of movement?
planning, initiating, and directing voluntary movements
what type of movement are brainstem centers ( upper motor neurons involved in?
basic movement and postural control
what is a difference in the upper motor neuron in brain stem vs. cerebral cortex in terms of descent? *** Check with dr. midleton’s answer first
the UMN on the brainstem has a bilateral effect on the proximal axial muslces and therefore synapse with the LMN in the medial ventral horns
the UMN in the cortex contralaterally affects the LMN of the distal limb muscles synapsing with the lower motor neurons in the MEDIAL? ventral horn
see page 828
what are the 2 categories of descending corticospinal terminations?
direct: synapse directly on spinal cord motor neuron
indirect: projections to the intermediate gray neurons ( interneurons)
what are priopriospinal neurons and what is another name for them?
propriospinal neurons are neurons that supply the medial and lateral regions of the ventral horns. they are also called local circuit neurons
describe the path of a short distance local circuit neuron ( propriospinal neuron) vs a long distance local circuit neuron ( propriospinal neuron)
the short distance local circuit ( propriospinal neuron) travels a short distance e.g. from the spinal cord level just above and travels to the lateral ventral horn which is for the distal limbs like the hand.
the long distance local circuit ( propriospinal neuron) travels a long distance and travels to the medial ventral horn which is for the axial muscles for posture
what is stiffling and what is indicative of?
stiffling looks like spikes on the ventral horn. it means there are more axons and the more stifling means the more dextrous, thus humans have lots of stiffling whereas cats don’t have much
why do infants have a postive babinksi sign?
because they don’t have direct terminations of axons on the lateral, ventral horn and therefore they are not as dextrous
what are the main indirect descending pathways and where do they project from?
the project from the brainstem
cortico-colliculo-spinal ( tecto spinal)
cortico-rubro spinal
cortico -reticulo spinal
cortico-vestibulo spinal
what are the direct pathways ( and where do they project from)?
the lateral cortico spinal
the medial cortico spinal
they start in the cortex ( the large pyramidal cells in layers III and V) and descend all the way down the ventral spinal cord
what does the vestibulospinal tract do?
changes gain of axial and proximal limb reflexes; anti gravity muscles
what does the reticulospinal tract do?
changes gain of axial and proximal limb reflexes: central pattern generator
what does the colliculospinal ( tectospinal) tract do?
axial and midline body orientation and takes auditory and visual cues ( makes sense because coming from colliculli which have visual and auditory input
what does the rubrospinal tract do?
some distal control mainly arm flexion
the most direct cortical motor innervation is coming from?
the primary motor cortex ( M1)
what are betz cells ?
cells in the primary motor cortex which have the largest projections b/c they are so big and b/c they havedirect projections to the alpha motor neurons ( only found in the motor areas)
how many motor cortex areas do we have?
7: 2 oculomotor and 5 skeletal motor
** know this: what are the criteria to be a skeletal motor area?
1.projection to the motor neuron in the spinal cord either direct (cortex to neuron) or indirect ( via interneuorns)
- projects to primary motor cortex
- contains betz cells or equivalent large layer V projection neurons
- can be stimulated at low thresholds to produce movements of discrete muscles or muscle groups
- displays changes in activity related to parameters of movement
do association area meet all the criteria of cortical motor areas?
no the prefrontal and posterior parietal areas collectively known as the association areas don’t meet all the criteria for being a cortical motor area but they do participate in the regulation of motor fnc
what does the premotor cortex consist of?
lateral premotor cortex: dorsal and ventral premotor areas
and
medial premotor cortex: supplementary motor cortex and cingulate motor areas
what doe the association areas consist of?
pre supplementary motor area, parietal and temporal corticies ( dorsal and ventral pathways), and prefrrontal cortex
what muscles do corticobulbar tract control?
muscles of the face
what did the experiment with lesion to the lateral cortical spinal tract on the monkeys show?
harder for monkey to exhibit fine motor control i.e. takes longer for them to grab the fruit but over time there is some restoration of fine motor control although the fine motor control is never fully restored.
what accounts for the recovery of some fine motor control?
there are local circuit neurons ( propriospinal neurons) above the lesion which are spared so they can project down to the lesioned area
although there is somatotopy of muscles there are various motor maps for the same muscles but what do we know about outputs from these disparate cortical motor areas?
they converge on a common set of motor neurons
1 corticospinal neuron in cortex can control __________ muscle(s)
multiple muscles ( usually involved in the same movement)
what does it mean that there is a fractured somatotopy?
cells w/ similar targets are NOT located adjacent to one another
how are columns of functionally related neurons connected?
by horizontal connections
how can the spread of epilepsy be prevented?
by cutting the most upper, superficial layer of affected area so that the motor area is still preserved but as much of lesion removed as possible.
how does spike triggered averaging work?
if you record from a single UMN and a muscle whose LMN may be affected who you can see if the EMG changes ( increase or decrease = excitatory or inhibitory respectively) this will allow you to tell if they are connected.
UMN an contact how many LMNs pools approx?
2-3 LMN pools of both agonist and antagonist muscles ( via inhibitory antagonists)
how many neurons in a LMN pool does an UMN synapse with?
probably all of the neurons in that pool
what 3 things do cortical motor cells code for?
muscle activity ( e.g flexion of the arm) force ( e.g. flex the loaded forearm) direction ( e.g flex and extend arm to point in a specific direction)
are neurons in the primary cortex concerned with the individual muscle activity or the direction of movement?
both: 1/3 of neurons in study showed that primary cortex motor neurons fire like the muscles when there is a change in position whereas there are about 50% of neurons that change direction irrespecitve of muscle movement thus they care about the direction more than the individual muscle movements
what has the strong relationship between the motor cortex activity and intended movement direction led to?
prosthetics that can move base on signals from the motor cortex even if person doesn’t have those muscles
does the motor cortex act alone?
no it has input from the association areas and the sensory inputs
what does the primary motor area code for?
execution of simple movements
the lateral premotor area codes for?
selection of responses based on externally- cued sensory inputs
the medial premotor area ( supplementary and cortical motor areas) code for?
executing learned sequences internally cued movements
the pre supplementary motor area codes for?
learned sequences
the prefrontal area codes for?
decision for action and working memory; monitoring outcomes
infromation is directly to motor areas from ?
from sensory areas
is fine sensory in the same or different area as other less fine sensory inputs?
i a different area
how important is the positional and stretch information?
very important: it can fool the motor system into thinking that it is moving
