Motor Cortical Areas

Question 1

What are the 4 motor cortical areas?

Answer 1

primary motor cortex

premotor cortex

supplementary motor cortex

frontal eye fields

Question 2

What are the 3 general deficits you’ll see in motor cortical area damage?

Answer 2

loss of voluntary movements

paresis

increased tone/stretch reflexes

Question 3

What are the 2 criteria for an area to be considered a motor cortical area?

Answer 3

1. cytoarchitecturally has to be agranular
2. stimulation of the area must evoke motor movement even at low stimulus intensities

Question 4

What does it mean that the area is agranular? What areas are granular?

Answer 4

motor areas are agranula because the granular layers (2 and 4) are underdeveloped and the pyramidal layers (3 an 5) are well developed

sensory areas are granular

Question 5

What are the two general opinions about what the primary motor cortex does?

Answer 5

1. controls indibidual muscles/forces by generating the motor command
2. Controls the more global features of movement, like direction and amplitude of reach

Question 6

What two structural features of the primary motor cortex have been revealed by stimulation?

Answer 6

1, motor homunculus

2. columnar organization - so within areas of representation for the thumb, there are columns that deal with specific movements of the thumb - specific spot for flesion, specific spot for adduction, etc.

this allows for very discrete movements

Question 7

Where does the afferent input FROM THE PERIPHERY to the primary motor cortex come from?

Answer 7

from the periphery bia the dorsal column nuclei (DCN) and VPL of the thalamus

• from joints
• from the spindle receptors
• and cutaneous input form the glaborous skin

Question 8

What brain regions provice afferent infromation tot he primary motor cortex?

Answer 8

cerebellum

basal ganglia

somatosensory cortex

premotor

supplementary motor

posterior parietal cortex

Question 9

What brain region in particular provides visual info to the primary motor cortex for spatial cognition

Answer 9

posterior parietal cortex (areas 5 and 7)

Question 10

What is the primary output projection from the primary motor cortex?

Answer 10

mostly through pyramidal neurons in the pyramidal tract

(which drops off innerfation at areas like the premotor, supplementary motor, somatosensory, frontal eye, etc. and then becomes the corticospinal tract)

Question 11

About how mnay axons make up the pyramidal tract?

Answer 11

2,000,000!

Question 12

While many textbooks say the pyramidal tract is made primarily of the giant Betz cells in area 4, what is the actual percentage?

Answer 12

only 3%

Question 13

Pyramidal cells going to the basal ganglia run in what tract?

Answer 13

corticostriate

Question 14

Pyramidal cells going to the red nucleus go in what tract?

Answer 14

the corticorubral tract

Question 15

Pyramidal cells going to the pons travel in what tract?

Answer 15

the corticopontine

Question 16

Pyramidal cells going to the reticular formation travel in what tract?

Answer 16

corticoreticular tract

Question 17

Pyramidal cells going to the cranial nerve nuclei travel in what tract?

Answer 17

corticobulbar

Question 18

Pyramidal fibers going to the spinal cord travel in what tract?

Answer 18

corticospinal

Question 19

The corticobulbar fibers specifically go to which 5 nuclei?

Answer 19

1. motor trigeminal
2. facial nucleus
3. nucleus ambiguus
4. spinal accessory nucleus
5. hypoglossal nucleus

Question 20

Are the fibers to the motor trigeminal mostly bilateral, ipsilateral or contralateral?

Answer 20

mostly bilateral

Question 21

How is innervation of the facial muscles a bit odd in terms of bilateral, ipsilateral or contralateral?

Answer 21

lower face is controlled by the contralateral nucleus ONLY

Upper face is controlled by both ipsilateral and contralateral motor cortex

so central damage will spare the forehead

Question 22

What muscles ar einnervated by fibers in the nucleus ambiguous? Bilateral, ipsilateral or contralateral?

Answer 22

muscles of th elaryngeal and upper airways - bilateral

Question 23

Is innervation form the spinal accessory nucleus bilateral, ipsilateral or contralateral?

Answer 23

ipsilateral

Question 24

Is inenrvation from the hypoglossal nucleus bilateral, ipsilateral or contralateral?

Answer 24

mostly contralateral

so with central damage, the tongue will project away from the side with the lesion

Question 25

Where do the frontal eye fields project to initially?

Answer 25

the brainstem gaze centers

these then project to the nuclei of CN3, CN4, and CN6

Question 26

Where does the corticospinal tract terminate for the most part?

hint: it’s a little ocunterintuitive

Answer 26

the dorsal horn of the spinal cord (also intermediate gray and a little in the ventrla horn)

it’s counterintuitive, but it does this so that you can have somatosensoty input into what the musclse are doing. Control is both sensory and motor in descending systems

Question 27

A single corticospinal axon diverges to ____-motoneurons of _____ muscles.

Answer 27

alpha motoneurons of many muscles

Question 28

What are the two general pieces of information the cells of the primary motor cortex can encode?

Answer 28

1. force and/or muscle activation
2. movement direction

Question 29

If the “load” the flexor to make it more difficult, the neuron will first action potentials of ___ amplitude

if the extensor is loaded such that flexing doesn’t take any effort, the neuron will fire action potentials of ___ amplitude

Answer 29

higher

lower - if it fires at all

Question 30

Describe population coding in the motor system.

Answer 30

cells will be broadly tuned to a movement parameter, and they’ll fire in a population to make the movement happen - each one contributes one slight aspect to the movement, not the whole thing - it takes the whole population of cells to do it

Question 31

What deficits would you see in someone if JUST their corticospinal tract was cut? What movement would still be intact?

Answer 31

Deficits in control of hand: loss of opposition of thumb and index finger, uses hand like a cup, loss of independent extension of one digit, cupping and scooping movements

But you’d still have intact reaching and locomotion

Question 32

Lesions of the primary motor cortex yields ___ motor neuron syndrome

Answer 32

upper

Question 33

What are the symptoms of an upper motor neuron syndrome? Bilateral, contralateral, ipsilater?

Answer 33

contralateral paresis, increased extensor tone, increased stretch reflexes

Question 34

What are the corticobulbar signs? When do they occur?

Answer 34

they occur with lesion of the primary motor cortex

1. lower facial muscle paralysis - contralateral
2. weakness of ipsilateral trapezius/SCM due to accessory nucleus loss
3. weakness of contralateral tongue cue to hypoglossal innervation loss

Question 35

What does stimulation of the premotor cortex cause and how is it different from stimulation of the primary motor cortex?

Answer 35

you get coordinated and synergistic movement

so contrlateral hand seems to lead and the head turns to “watch” for examples

this is much higher order than what you get with primary motor cortex stimulation

Question 36

What are the general fun

Answer 36

1. involved with sensorimotor transformation (taking sensory cue and turning it to muscle action)
2. so…obviously planning and learning is a big deal

***particularly involved with reaching for things***

Question 37

What are the two parts of the premotor cortex and how are their jobs different?

Answer 37

the dorsal premotor area is for arm movement

the ventral premotor area is for hand movement

Question 38

What stimulation results support the idea that the premotor area is involved in planning of movement?

Answer 38

monkeys are given an instruction signal (of where to move their hand) and they’re trained to wait until a “trigger” signal before they actually move

the premotor cortex neurons start firing after the instruction signal and continue until after the trigger signal

Question 39

What happens in lesion of the premotor cortex?

Answer 39

You lose the planning of movement in relation to sensory input.

Basically, the internally generated plan for movement is there, but you don’t have the externally generated arm of it. So patient can mime what to do with a toothbrush, but when given a toothbrush, they can’t do it - apraxia

they can’t steer their arms accuratley and cna’t execute compleex motor plans requiring ivsuomotor transofrmation (like reaching around a barrier to get some food)

In general, just can’t learn new sensory motor associations

Question 40

What special neurons are located in the ventral and dorsal premotor areas that fire when you see someone doing something

Answer 40

mirror neurons

Question 41

What are the three potential purposes for the mirror neurons?

Answer 41

1. imitation as a means of learning
2. A way to understand the action someone else is doing
3. A way to gauge the intentions of the other person

Question 42

What does stimulation of the supplementary motor area elicit?

Answer 42

contralateral movement of multiple joins and postural changes

arrange in a homunculus with face rostral and leg caudal

Question 43

What are the two main supplementary motor area functions?

Answer 43

1. INTERNAL generation of movements
2. sequence of learned movements

Question 44

When do SMA neurons become particularly with large bereitshaft potentials?

Answer 44

prior to self-initiated movements (internally generated movements)

Question 45

Neuorns in the SMA discharge in relation to specific ____ of internally guided movements.

Answer 45

sequences

Question 46

What will happen with lesions of the SMA?

Answer 46

1. patients become stimulus bound; showing utilizATion behaviors
2. Alien hand syndrome
3. Trouble executing learned sequences (make semi-purposeful movements apparently outside of their control)

Question 47

What are utilization behaviors?

Answer 47

where the patient does automatic movements/behaviors based on any stimulus they are given

if given two pairs of glasses they’ll put them both on

Question 48

What are the two aspects of alien hand syndrome?

Answer 48

patients won’t recognize the hand as their own

thehand will do things that seem to be in opposition of the other hand - like unbuttoning a shirt they just buttoned

Question 49

As a motor tasks becomes highly profieicnt, what happens to the SMA’s role?

Answer 49

it reduces its activity and the motor cortex primarily takes control