section 3- part 2 motor circuits Flashcards
what are the two descending motor networks? which is direct, which indirect?
- pyramidal (direct)
- brainstem-spinal (indirect)–aka extra pyramidal
what are the 4 components of the pyramidal direct system?
- corticobulbar
- corticopontine
- cortico-rubro-olivary
- corticospinal
what are the origin of the tracks of the pyramidal (direct) system?
all areas of the neocortex (esp frontal & parietal lobes)
what are the 4 component tracks of the brainstem-spinal system?
- vestibulospinal
- tectospinal
- reticulospinal
- rubrospinal
what are the origins of the tracts in the brainstem-spinal system?
- vestibular nuclei
- tectum
- reticular formation
- red nucleus
what tract does this describe:
“ from the neocortex, descends through the brainstem and controls neurons of all the cranial nerve nuclei”
the cortiobulbar track
a unilateral pathology of the cortiobulbar tract will weaken movement of the head/neck on which side
the side OPPOSITE of the lesion
why doesn’t unilateral pathology of the corticobulbar tract weaken significantly the muscles served by the cranial nerve nuclei?
because most cranial nerve nuclei also have an ipsilateral component of innervation
what two nerves are the real only two nerves that you will see symptoms of with a unilateral corticobulbar lesion?
the hypoglossal (12) nerve affecting tongue deviation and the facial (7) nerve
what tract does this describe:
“from the neocortex, descends to terminate on the pontine nuclei”
corticopontine tract
from the pontine nuclei, where do axons of the corticopontine track usually project to?
to the cerebellum on the opposite side
note: you don’t really see isolated damage to this tract
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”
cortico-rubro-olivary circuit
what type of name is that?!?!
what does the cortico-spinal tract control?
motor neurons of the trunk & limbs
in the brainstem, what side does the corticospinal tract descend on?
on the SAME side as their cortical origin
where do most axons of the corticospinal tract cross?
cross at the midline in the caudal medulla (pyramidal decussation)
in the spinal cord, what side does the cortiospinal tract descend on?
on the OPPOSITE side of their origin (but technically same side as the muscle they innervate & where the symptoms present–think about it)
what is the ventral/anterior corticospinal tract?
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)
pathology of the CS tract in the brainstem will impair movement on which side?
the symptoms will be on the OPPOSITE side
pathology of the CS tract in the spinal cord will impair movement on which side?
the symptoms will be on the SAME side
where do the brainstem-spinal pathways originate
in the brain stem
DUH
what does the brainstem-spinal pathways control?
the muscles of the neck, trunk & limbs
if there is a pathology of the brainstem-spinal pathway in the brainstem which side of the body will have affected movement?
the opposite side
if there is a pathology of the brainstem-spinal pathway in the spinal cord which side of the body will have affected movement?
same side
why do frontal lobe lesions often cause severe paraylysis?
because the precentral (motor) and premotor areas of the cortex contribute to both direct & indirect motor pathways
where do most of the axons of the pyramidal tract arise from?
the frontal gyri
besides the pyramidal tract, list 3 other places that the frontal cortex projects to
- brainstem nuclei
- cerebellum
- basal ganglia
what side is the pathology for…
peripheral nerve lesions
will lie on the SAME side as the lesions
what side is the pathology for…
spinal cord lesions
(note: also list the 1 exception to this rule)
lie on the SAME side as all of the symptoms
EXCEPT pain & temp (which travel in the anterolateral system which cross at entry)
what side is the pathology for…
brainstem lesion
it will lie on the SAME side as the most ROSTRAL symptom, and on the side OPPOSITE of the CAUDAL symptoms
what side is the pathology for…
forebrain lesion
OPPOSITE side of symptoms
what side is the pathology for…
cerebellum lesion
SAME side as symptoms
list the 2 factors that are responsible for maintaining the usual tone of our mucles
- the sensory fibers from muscle spindles which synapse on motor neurons on the cord
- the corticospinal (direct) and brainstem (indirect) motor pathways
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?
the deep tendon reflex
what are two names that describe a muscle whose contraction is less than normal? what type of reflex do these muscles produce?
hypotonic
flaccid
hyporeflexive reponse
when a limb is stiffer and the reflex is “snapper” than usual, what are the terms to describe it?
hypertonic
hyperreflexic
what are two defects that can cause muscles to have lower tone?
- dorsal root disease- reducing sensory input into the cord from the spindles
- ventral root disease- reducing the output from the cord to the muscles
both are peripheral nerve diseases
with which type of peripheral nerve disease will you see fasciculations? why does this happen?
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”
what will happen to tone in a pathology of a central descending motor track? acutely & chronically
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
for the facial muscles:
if the facial nucleus or nerve is damaged (lower motor neuron paralysis) what will the be result?
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
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?
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
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?
this is because there is an intact descending corticobulbar projection from the cingulate gyrus that projects bilaterally to the facial muscles
