section 3- part 2 motor circuits

Question 1

what are the two descending motor networks? which is direct, which indirect?

Answer 1

• pyramidal (direct)

- brainstem-spinal (indirect)–aka extra pyramidal

Question 2

what are the 4 components of the pyramidal direct system?

Answer 2

1. corticobulbar
2. corticopontine
3. cortico-rubro-olivary
4. corticospinal

Question 3

what are the origin of the tracks of the pyramidal (direct) system?

Answer 3

all areas of the neocortex (esp frontal & parietal lobes)

Question 4

what are the 4 component tracks of the brainstem-spinal system?

Answer 4

1. vestibulospinal
2. tectospinal
3. reticulospinal
4. rubrospinal

Question 5

what are the origins of the tracts in the brainstem-spinal system?

Answer 5

1. vestibular nuclei
2. tectum
3. reticular formation
4. red nucleus

Question 6

what tract does this describe:

“ from the neocortex, descends through the brainstem and controls neurons of all the cranial nerve nuclei”

Answer 6

the cortiobulbar track

Question 7

a unilateral pathology of the cortiobulbar tract will weaken movement of the head/neck on which side

Answer 7

the side OPPOSITE of the lesion

Question 8

why doesn’t unilateral pathology of the corticobulbar tract weaken significantly the muscles served by the cranial nerve nuclei?

Answer 8

because most cranial nerve nuclei also have an ipsilateral component of innervation

Question 9

what two nerves are the real only two nerves that you will see symptoms of with a unilateral corticobulbar lesion?

Answer 9

the hypoglossal (12) nerve affecting tongue deviation and the facial (7) nerve

Question 10

what tract does this describe:

“from the neocortex, descends to terminate on the pontine nuclei”

Answer 10

corticopontine tract

Question 11

from the pontine nuclei, where do axons of the corticopontine track usually project to?

Answer 11

to the cerebellum on the opposite side

note: you don’t really see isolated damage to this tract

Question 12

what tract does this describe:

“sends connections to a portion of the red nucleus that in turn projects to inferior olive then to the cerebellum”

Answer 12

cortico-rubro-olivary circuit

what type of name is that?!?!

Question 13

what does the cortico-spinal tract control?

Answer 13

motor neurons of the trunk & limbs

Question 14

in the brainstem, what side does the corticospinal tract descend on?

Answer 14

on the SAME side as their cortical origin

Question 15

where do most axons of the corticospinal tract cross?

Answer 15

cross at the midline in the caudal medulla (pyramidal decussation)

Question 16

in the spinal cord, what side does the cortiospinal tract descend on?

Answer 16

on the OPPOSITE side of their origin (but technically same side as the muscle they innervate & where the symptoms present–think about it)

Question 17

what is the ventral/anterior corticospinal tract?

Answer 17

this is only a small number of the corticospinal axons actually continue ipsilaterally (remember from the other card, most of the CS tract axons will cross over and travel contralaterally on the spinal cord)

Question 18

pathology of the CS tract in the brainstem will impair movement on which side?

Answer 18

the symptoms will be on the OPPOSITE side

Question 19

pathology of the CS tract in the spinal cord will impair movement on which side?

Answer 19

the symptoms will be on the SAME side

Question 20

where do the brainstem-spinal pathways originate

Answer 20

in the brain stem

DUH

Question 21

what does the brainstem-spinal pathways control?

Answer 21

the muscles of the neck, trunk & limbs

Question 22

if there is a pathology of the brainstem-spinal pathway in the brainstem which side of the body will have affected movement?

Answer 22

the opposite side

Question 23

if there is a pathology of the brainstem-spinal pathway in the spinal cord which side of the body will have affected movement?

Answer 23

same side

Question 24

why do frontal lobe lesions often cause severe paraylysis?

Answer 24

because the precentral (motor) and premotor areas of the cortex contribute to both direct & indirect motor pathways

Question 25

where do most of the axons of the pyramidal tract arise from?

Answer 25

the frontal gyri

Question 26

besides the pyramidal tract, list 3 other places that the frontal cortex projects to

Answer 26

1. brainstem nuclei
2. cerebellum
3. basal ganglia

Question 27

what side is the pathology for…

peripheral nerve lesions

Answer 27

will lie on the SAME side as the lesions

Question 28

what side is the pathology for…
spinal cord lesions
(note: also list the 1 exception to this rule)

Answer 28

lie on the SAME side as all of the symptoms

EXCEPT pain & temp (which travel in the anterolateral system which cross at entry)

Question 29

what side is the pathology for…

brainstem lesion

Answer 29

it will lie on the SAME side as the most ROSTRAL symptom, and on the side OPPOSITE of the CAUDAL symptoms

Question 30

what side is the pathology for…

forebrain lesion

Answer 30

OPPOSITE side of symptoms

Question 31

what side is the pathology for…

cerebellum lesion

Answer 31

SAME side as symptoms

Question 32

list the 2 factors that are responsible for maintaining the usual tone of our mucles

Answer 32

1. the sensory fibers from muscle spindles which synapse on motor neurons on the cord
2. the corticospinal (direct) and brainstem (indirect) motor pathways

Question 33

when striking a knee with a rubber hammer, what is the name of the reflex that is responsible for speed and amplitude of the “jerk” that this action produces?

Answer 33

the deep tendon reflex

Question 34

what are two names that describe a muscle whose contraction is less than normal? what type of reflex do these muscles produce?

Answer 34

hypotonic
flaccid

hyporeflexive reponse

Question 35

when a limb is stiffer and the reflex is “snapper” than usual, what are the terms to describe it?

Answer 35

hypertonic

hyperreflexic

Question 36

what are two defects that can cause muscles to have lower tone?

Answer 36

1. dorsal root disease- reducing sensory input into the cord from the spindles
2. ventral root disease- reducing the output from the cord to the muscles

both are peripheral nerve diseases

Question 37

with which type of peripheral nerve disease will you see fasciculations? why does this happen?

Answer 37

you will see it in ventral (MOTOR) peripheral nerve damage.
it occurs because loss of motor input causes the death of the muscles being innervated and this is how the muscles “publicize their demise”

Question 38

what will happen to tone in a pathology of a central descending motor track? acutely & chronically

Answer 38

acutely-tone will be lowered due to sudden loss of descending connections
chronically- limb becomes hypertonic & hyperreflexic because the residual influence on motor neurons is predominantly excitatory

Question 39

for the facial muscles:

if the facial nucleus or nerve is damaged (lower motor neuron paralysis) what will the be result?

Answer 39

the entire ipsilateral side of the face is weakened or paralyzed
ex. if pathology is in the LEFT pons (where the facial nerve nucleus is) then the LEFT half of the patient’s face will be weak

Question 40

for the facial muscles:
if the paralysis is of the “upper motor neuron” type (which could be due to pathology in forebrain or corticobulbar tract) what will the result be?

Answer 40

only the lower quadrant of the face will be paralyzed on the OPPOSITE SIDE

this is example of when a person has a uneven (non emotional) smile but the wrinkles on their forehead are fine

Question 41

why is that after a middle cerebral artery stroke, patients who have contralateral lower facial paralysis are still able to smile (as a emotionally response) normally?

Answer 41

this is because there is an intact descending corticobulbar projection from the cingulate gyrus that projects bilaterally to the facial muscles