Motor Cortical Areas Flashcards
What are the 4 motor cortical areas?
primary motor cortex
premotor cortex
supplementary motor cortex
frontal eye fields
What are the 3 general deficits you’ll see in motor cortical area damage?
loss of voluntary movements
paresis
increased tone/stretch reflexes
What are the 2 criteria for an area to be considered a motor cortical area?
- cytoarchitecturally has to be agranular
- stimulation of the area must evoke motor movement even at low stimulus intensities
What does it mean that the area is agranular? What areas are granular?
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
What are the two general opinions about what the primary motor cortex does?
- controls indibidual muscles/forces by generating the motor command
- Controls the more global features of movement, like direction and amplitude of reach
What two structural features of the primary motor cortex have been revealed by stimulation?
1, motor homunculus
- 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
Where does the afferent input FROM THE PERIPHERY to the primary motor cortex come from?
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
What brain regions provice afferent infromation tot he primary motor cortex?
cerebellum
basal ganglia
somatosensory cortex
premotor
supplementary motor
posterior parietal cortex
What brain region in particular provides visual info to the primary motor cortex for spatial cognition
posterior parietal cortex (areas 5 and 7)
What is the primary output projection from the primary motor cortex?
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)
About how mnay axons make up the pyramidal tract?
2,000,000!
While many textbooks say the pyramidal tract is made primarily of the giant Betz cells in area 4, what is the actual percentage?
only 3%
Pyramidal cells going to the basal ganglia run in what tract?
corticostriate
Pyramidal cells going to the red nucleus go in what tract?
the corticorubral tract
Pyramidal cells going to the pons travel in what tract?
the corticopontine
Pyramidal cells going to the reticular formation travel in what tract?
corticoreticular tract
Pyramidal cells going to the cranial nerve nuclei travel in what tract?
corticobulbar
Pyramidal fibers going to the spinal cord travel in what tract?
corticospinal
The corticobulbar fibers specifically go to which 5 nuclei?
- motor trigeminal
- facial nucleus
- nucleus ambiguus
- spinal accessory nucleus
- hypoglossal nucleus
Are the fibers to the motor trigeminal mostly bilateral, ipsilateral or contralateral?
mostly bilateral
How is innervation of the facial muscles a bit odd in terms of bilateral, ipsilateral or contralateral?
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
What muscles ar einnervated by fibers in the nucleus ambiguous? Bilateral, ipsilateral or contralateral?
muscles of th elaryngeal and upper airways - bilateral
Is innervation form the spinal accessory nucleus bilateral, ipsilateral or contralateral?
ipsilateral
Is inenrvation from the hypoglossal nucleus bilateral, ipsilateral or contralateral?
mostly contralateral
so with central damage, the tongue will project away from the side with the lesion
Where do the frontal eye fields project to initially?
the brainstem gaze centers
these then project to the nuclei of CN3, CN4, and CN6
Where does the corticospinal tract terminate for the most part?
hint: it’s a little ocunterintuitive
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
A single corticospinal axon diverges to ____-motoneurons of _____ muscles.
alpha motoneurons of many muscles
What are the two general pieces of information the cells of the primary motor cortex can encode?
- force and/or muscle activation
- movement direction
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
higher
lower - if it fires at all
Describe population coding in the motor system.
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
What deficits would you see in someone if JUST their corticospinal tract was cut? What movement would still be intact?
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
Lesions of the primary motor cortex yields ___ motor neuron syndrome
upper
What are the symptoms of an upper motor neuron syndrome? Bilateral, contralateral, ipsilater?
contralateral paresis, increased extensor tone, increased stretch reflexes
What are the corticobulbar signs? When do they occur?
they occur with lesion of the primary motor cortex
- lower facial muscle paralysis - contralateral
- weakness of ipsilateral trapezius/SCM due to accessory nucleus loss
- weakness of contralateral tongue cue to hypoglossal innervation loss
What does stimulation of the premotor cortex cause and how is it different from stimulation of the primary motor cortex?
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
What are the general fun
- involved with sensorimotor transformation (taking sensory cue and turning it to muscle action)
- so…obviously planning and learning is a big deal
***particularly involved with reaching for things***
What are the two parts of the premotor cortex and how are their jobs different?
the dorsal premotor area is for arm movement
the ventral premotor area is for hand movement
What stimulation results support the idea that the premotor area is involved in planning of movement?
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
What happens in lesion of the premotor cortex?
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
What special neurons are located in the ventral and dorsal premotor areas that fire when you see someone doing something
mirror neurons
What are the three potential purposes for the mirror neurons?
- imitation as a means of learning
- A way to understand the action someone else is doing
- A way to gauge the intentions of the other person
What does stimulation of the supplementary motor area elicit?
contralateral movement of multiple joins and postural changes
arrange in a homunculus with face rostral and leg caudal
What are the two main supplementary motor area functions?
- INTERNAL generation of movements
- sequence of learned movements
When do SMA neurons become particularly with large bereitshaft potentials?
prior to self-initiated movements (internally generated movements)
Neuorns in the SMA discharge in relation to specific ____ of internally guided movements.
sequences
What will happen with lesions of the SMA?
- patients become stimulus bound; showing utilizATion behaviors
- Alien hand syndrome
- Trouble executing learned sequences (make semi-purposeful movements apparently outside of their control)
What are utilization behaviors?
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
What are the two aspects of alien hand syndrome?
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
As a motor tasks becomes highly profieicnt, what happens to the SMA’s role?
it reduces its activity and the motor cortex primarily takes control
