Chapter 17- Upper Motor Neuron Control of Brainstem and Spinal Cord

Question 1

how will the upper motor neurons relay to lower motor neurons ?

Answer 1

upper motor neurons from cortex will go to lower motor neurons in medial ventral horn, and will control distal limb muscles

upper motor neurons from brainstem will go to lower motor neurons in medial ventral horn, and will control axial and proximal limb muscles for posture and balance

Question 2

how many areas are there in the primary motor cortex ? which layers are for output and input ? what

Answer 2

6 areas

area 4 input
area 5 output

pyramidal cells ending in brainstem (corticobulbar) or spinal cord (corticospinal).

Question 3

what is the corticospinal tract ?

Answer 3

involved in voluntary movement

cross over at pyramids

Question 4

what is the corticobulbar tract ?

Answer 4

goes from PMC to brainstem
(terminates in pons, medulla)
synapse with interneurons or directly with lower motor neurons of facial nerves

Question 5

how is the motor homunculus divided in tracts ?

Answer 5

face (lateral) is corticobulbar

rest of body (medial) is corticospinal

Question 6

do neurons fire in relation to production of force or movement in the PMC ?

Answer 6

both

Question 7

discuss the motor maps in the PMC

Answer 7

basic movements, like “reach”, “hand to mouth” seem to be represented in the PMC

Question 8

how can the influence of single cortical upper motor neurons on muscle activity be observed ?

Answer 8

record from single cortical motor neuron, and then observe the spikes in activity
also connect to EMG and observe EMG of muscle
the EMG amplitude will go up right after postspike facilitation by cortical motor neuron

Question 9

explain the idea of directionally tuned neurons

Answer 9

firing pattern is different in different directions. there is an optimal direction for every neuron and you will see an increase in firing rate

Question 10

how would we improve the precision of the calculation of the resultant vector ?

Answer 10

add neurons

Question 11

what is the lateral premotor cortex good for ?

Answer 11

stimulus- triggered, receives stimulus and plans to make a movement in association to that stimulus, like in sports

Question 12

what are the supplementary motor areas good for ?

Answer 12

self-generated movement

Question 13

what is the cingulate motor area good for ?

Answer 13

emotionally triggered, like moving in anger or fear

Question 14

what do mirror neurons do that’s unexpected ?

Answer 14

AP response increases when someone else produces the same movement

Question 15

what is the reticulospinal tract ? what is it used for ?

Answer 15

an indirect pathway from the motor cortex to the spinal cord
PMC projects to reticular formation
that goes to spinal cord

it integrates information from the motor systems to coordinate posture

therefore the pathway is involved before and during movement production, especially for babies

Question 16

in an EMG how will we see the anticipatory maintenance of body posture by the corticoreticulospinal tract ?

Answer 16

EMG of gastroc shows activation before EMG of biceps (pulling lever that creates balance perturbation)

Question 17

what is the feedforward mechanism for posture ?

Answer 17

central command feedforward for anticipated postural instability- dual planning of limb movement and posture

Question 18

what is the feedback mechanism for posture ?

Answer 18

there is a constant feedback from limbs for postural adjustment during movement

Question 19

what would an upper motor neuron lesion look like on the face ?

Answer 19

weakness of inferior facial muscles on one side

Question 20

what would a lower motor neuron lesion look like on the face ?

Answer 20

weakness of superior and inferior facial muscles on one side