upper motor neurons and cortical control of movement

Question 1

what are the main motor structures in the CNS?

Answer 1

in order of highest to lowest: assoc. cortex, cortical motor areas, basal ganglia, cerebellum, spinal cord

Question 2

what do the lower level of motor control ( e.g. spinal cord) vs. the higher ( e.g. cortex)

Answer 2

low levels accomplish most of the automatic behaviors, while high levels do more of the complex planning and selection

Question 3

motor cortex ( upper motor neurons) is involved in what type of movement?

Answer 3

planning, initiating, and directing voluntary movements

Question 4

what type of movement are brainstem centers ( upper motor neurons involved in?

Answer 4

basic movement and postural control

Question 5

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

Answer 5

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

Question 6

what are the 2 categories of descending corticospinal terminations?

Answer 6

direct: synapse directly on spinal cord motor neuron
indirect: projections to the intermediate gray neurons ( interneurons)

Question 7

what are priopriospinal neurons and what is another name for them?

Answer 7

propriospinal neurons are neurons that supply the medial and lateral regions of the ventral horns. they are also called local circuit neurons

Question 8

describe the path of a short distance local circuit neuron ( propriospinal neuron) vs a long distance local circuit neuron ( propriospinal neuron)

Answer 8

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

Question 9

what is stiffling and what is indicative of?

Answer 9

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

Question 10

why do infants have a postive babinksi sign?

Answer 10

because they don’t have direct terminations of axons on the lateral, ventral horn and therefore they are not as dextrous

Question 11

what are the main indirect descending pathways and where do they project from?

Answer 11

the project from the brainstem

cortico-colliculo-spinal ( tecto spinal)
cortico-rubro spinal
cortico -reticulo spinal
cortico-vestibulo spinal

Question 12

what are the direct pathways ( and where do they project from)?

Answer 12

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

Question 13

what does the vestibulospinal tract do?

Answer 13

changes gain of axial and proximal limb reflexes; anti gravity muscles

Question 14

what does the reticulospinal tract do?

Answer 14

changes gain of axial and proximal limb reflexes: central pattern generator

Question 15

what does the colliculospinal ( tectospinal) tract do?

Answer 15

axial and midline body orientation and takes auditory and visual cues ( makes sense because coming from colliculli which have visual and auditory input

Question 16

what does the rubrospinal tract do?

Answer 16

some distal control mainly arm flexion

Question 17

the most direct cortical motor innervation is coming from?

Answer 17

the primary motor cortex ( M1)

Question 18

what are betz cells ?

Answer 18

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)

Question 19

how many motor cortex areas do we have?

Answer 19

7: 2 oculomotor and 5 skeletal motor

Question 20

** know this: what are the criteria to be a skeletal motor area?

Answer 20

1.projection to the motor neuron in the spinal cord either direct (cortex to neuron) or indirect ( via interneuorns)

2. projects to primary motor cortex
3. contains betz cells or equivalent large layer V projection neurons
4. can be stimulated at low thresholds to produce movements of discrete muscles or muscle groups
5. displays changes in activity related to parameters of movement

Question 21

do association area meet all the criteria of cortical motor areas?

Answer 21

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

Question 22

what does the premotor cortex consist of?

Answer 22

lateral premotor cortex: dorsal and ventral premotor areas
and
medial premotor cortex: supplementary motor cortex and cingulate motor areas

Question 23

what doe the association areas consist of?

Answer 23

pre supplementary motor area, parietal and temporal corticies ( dorsal and ventral pathways), and prefrrontal cortex

Question 24

what muscles do corticobulbar tract control?

Answer 24

muscles of the face

Question 25

what did the experiment with lesion to the lateral cortical spinal tract on the monkeys show?

Answer 25

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.

Question 26

what accounts for the recovery of some fine motor control?

Answer 26

there are local circuit neurons ( propriospinal neurons) above the lesion which are spared so they can project down to the lesioned area

Question 27

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?

Answer 27

they converge on a common set of motor neurons

Question 28

1 corticospinal neuron in cortex can control __________ muscle(s)

Answer 28

multiple muscles ( usually involved in the same movement)

Question 29

what does it mean that there is a fractured somatotopy?

Answer 29

cells w/ similar targets are NOT located adjacent to one another

Question 30

how are columns of functionally related neurons connected?

Answer 30

by horizontal connections

Question 31

how can the spread of epilepsy be prevented?

Answer 31

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.

Question 32

how does spike triggered averaging work?

Answer 32

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.

Question 33

UMN an contact how many LMNs pools approx?

Answer 33

2-3 LMN pools of both agonist and antagonist muscles ( via inhibitory antagonists)

Question 34

how many neurons in a LMN pool does an UMN synapse with?

Answer 34

probably all of the neurons in that pool

Question 35

what 3 things do cortical motor cells code for?

Answer 35

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)

Question 36

are neurons in the primary cortex concerned with the individual muscle activity or the direction of movement?

Answer 36

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

Question 37

what has the strong relationship between the motor cortex activity and intended movement direction led to?

Answer 37

prosthetics that can move base on signals from the motor cortex even if person doesn’t have those muscles

Question 38

does the motor cortex act alone?

Answer 38

no it has input from the association areas and the sensory inputs

Question 39

what does the primary motor area code for?

Answer 39

execution of simple movements

Question 40

the lateral premotor area codes for?

Answer 40

selection of responses based on externally- cued sensory inputs

Question 41

the medial premotor area ( supplementary and cortical motor areas) code for?

Answer 41

executing learned sequences internally cued movements

Question 42

the pre supplementary motor area codes for?

Answer 42

learned sequences

Question 43

the prefrontal area codes for?

Answer 43

decision for action and working memory; monitoring outcomes

Question 44

infromation is directly to motor areas from ?

Answer 44

from sensory areas

Question 45

is fine sensory in the same or different area as other less fine sensory inputs?

Answer 45

i a different area

Question 46

how important is the positional and stretch information?

Answer 46

very important: it can fool the motor system into thinking that it is moving