Motor Flashcards
what happens if you knock out part of the genu of the internal capsule?
wipe out entire facial function (corticobulbar tract)
-muscles for the face, head, neck, upper shoulders
the corticobulbar tract is part of what system?
It controls what?
pyramidal system
head, neck, shoulder movement
Does the corticobulbar system decussate and if so where?
does NOT have a major decussation at the pyramids
travels down the brainstem ipsilaterally and then synapses with cranial nerve nuclei. The cranial nerve nuclei then send out branches bilaterally except for the facial and hypoglossal nerves.
how does the corticobulbar tract innervate?
usually bilaterally
where does the corticobulbar tract synapse?
in brainstem with cranial nerves - branches sent out bilaterally
-Thus, they are the axons of the upper motor
neurons that synapse on the lower motor neurons of the cranial nerves
what nerves have a direct pathway (for synapsing) onto muscle in the corticobulbar tract?
only the facial, trigeminal and hypoglossal nerve do. All others have to use an inteneuron
what are two exceptions to the corticobulbar tract?
the facial and hypoglossal nerves
stroke on the left side how does it affect the facial nerve?
weakness not complete palsy to contralateral side.
-right face will droop below the eye except you can wrinkle your forehead
stroke on the right side how does it affect the hypoglossal nerve?
weakness of tongue on left side = contralateral
what type of nuclei does the corticobulbar tract supply to cranial nerves?
motor nuclei
do the corticospinal tracts decussate and if so where?
90% decussate at the pyramids of the medulla
what side does the corticospinal tract control
mostly contralateral side
what are the different percents of tracts in the corticospinal tract?
lateral corticospinal tract= 90%
uncrossed lateral corticospinal tract = 2%
anterior corticospinal tract = 8%
what are the 3 sections of the internal capsule?
anterior limb
genu
posterior limb
what does the anterior of the internal capsule do?
frontal functions - not clinically relevant
what does the genu of the internal capsule do?
corticobulbar (face)
what does the posterior limb of the internal capsule do?
corticospinal tracts (down below head) -motor deficiencies
where does the corticobulbar tract travel in the internal capsule?
genu
the rest of the CNS system exists to modify what?
the reflex arc
what does the stretch reflex do?
When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases. This increases alpha motor neuron activity, causing the muscle fibers to contract and thus resist the stretching. A secondary set of neurons also causes the opposing muscle to relax. The reflex functions to maintain the muscle at a constant length.
giant pyramidal motor nerons
synapse on what?
other info
synapse on alpha motor neurons
largest CNS neurons
long projection neurons
where is the internal capsule located?
continuous with what?
- between the thalamus and basal ganglia
- continuous with the cerebral peduncle
motor cortex controls what side?
mostly contralateral side
anterior corticospinal tract
what does it control?
what side?
controls posture and balance
-ipsilateral control of proximal muscles
-contralteral control down lower bc decussates lower at the lower medulla
8%
uncrossed lateral corticospinal tract
function?
%?
2%
-may aid in recovery of stroke of the opposite side
does the corticospinal tract decussate and if so where?
90% decusasates at the pyramids of the medulla
8% the anterior corticospinal tract has both ipsilateteral and contralateral control. Contralateral decussates in lower medulla
what system is the basal ganglia part of?
extra pyramidal system
what does the basal ganglia do?
initiation, termination and amplitude of intentional movements
basal ganglia affects which side?
contralateral side
striatum components
caudate + putamen
lenticular nucleus components
putamen + globus pallidus
ventral pallidum components
base of caudate head and ventral putamen - limbic
blood supply of the basal ganglia?
internal carotid artery - branches of and btwn the anterior and middle cerebral arteries
basal ganglia input
- caudate
2. putamen
output of basal ganglia?
- globus pallidus internal segment
2. substantia nigra : pars reticulata
intrinsic basal ganglia?
- globus pallidus external segment
2. subthalamic nucleus
modulatory component of the basal ganglia?
substantia nigra: pars compacta
the direct pathway function?
initiate an action
indirect pathway function?
terminate an action
two negatives make a ?
positive
the cortex send positive signals to the _____ which activates it
the striatum
the striatum send out 2 ______ signals to what 2 structures?
2 negative (inhibitory) signals- one to the globus pallidus external segment (indirect) and one to the globus pallidus internal segment/ substantia nigra reticulata (direct pathway)
movement modulation occurs via _________ of the thalamus
disinhibition of the thalamus = movement
- the globus pallidus external segment does what in the basal ganglia circuit?
- a strong inhibitory signal from the globus pallidus has what affect on the indirect system?
- it inhibits the subthalamic nucleus.
- A strong inhibatory signal from the globus pallidus external segment inhibits the subthalamic nucleus causing a small excitatory signal to be released = good.
what does a large excitatory signal from the subthalamic nucleus do to the thalamus?
a large excitatory signal released from the subthalamic nucleus excited the globus pallidus internal segment/ substantia nigra reticulata to produce a large inhibitory stimulus that prevents the thalamus from generating movement.
what does a strong signal from the striatum to the globus pallidus internal segment/ substantia nigra reticulata do?
it inhibits the globus pallidus internal segment/ substantia nigra reticulata which produces a small inhibitory signal to the thalamus which promotes movement
what part of the basal ganglia circuit does Huntington’s disease target?
-primary symptom?
-Huntington’s Disease targets the indirect pathway signal from the striatum to the globus pallidus external segment
= hyperkinesis b/c indirect pathway (prevents movement) - overactivity
what part of the basal ganglia circuit does Parkinson’s disease target?
-primary symptom?
Parkinson’s disease
-direct pathway = less active = hypokinesis
thus the indirect pathway is active
what does a pallidotomy target?
treatment for what disease?
how?
- damages/ ablates the globus pallidus internal segment/ substantia nigra to treat parkinson’s disease.
- it damages the signals sent to the thalamus so that more movements are possible by eliminating more inhibition.
- problems = inflammation years down the road
what area of the basal ganglia does hemiballism affect?
main symptoms
hemibalism = a lesion to the subthalamic nucleus
-abnormal movements
Function of output nuclei?
output nuclei such as the _____ are excitatory or inhibitory?
-output nuclei maintain a high level of discharge to suppress areas.
ex the subthalamic nucleus keeps a high level of output to activate the globus pallidus internal segment/ substantia nigra reticulata to have it send out a strong signal to inhibit the thalamus
where does deep brain stimulation target?
therapy for what disease?
targets the subthalamic nucleus
- parkinson’s disease
- this makes the indirect pathway less active so the patients can use the direct pathway to start a movement
what is Levadopa and what can it do?
Levadopa is a drug for parkinson’s disease patients that compensates for a loss of dopa receptors in the substantia nigra
firing rate of striatal neurons?
require what?
low tonic firing rates
require strong cortical input
what occurs under resting conditions of the striatal neurons?
striatal output does not inhibit globus pallidus internal/ substantia nigra reticulata enough
do you want a large or small input to the cortex to the striatum for the direct pathway to activate the thalamus?
What is the pathway?
huge input = large inhibition of globus pallidus interna/ substantia nigra reticulata, smaller inhibition of thalamus released = activation of thalamus
the indirect pathway components (globus pallidus external segment) and subthalamic nucleus have ____ firing rates?
high tonic firing rates
do you want a large or small input to the cortex to the striatum for the indirect pathway to inhibit the thalamus?
What is the pathway?
large input from cortex to striatum causes the globus pallidus to be inhibited which causes the subthalmic nucleus to be less inhibited which causes a large excitatory signal to travel to the globus pallidus internal segment/ substantia nigra reticulata. The GPI/ SNR then sends out s strong inhibitory signal to the thalamus to inhibit and suppress action
what does hyperkinesia do to the neurons?
example?
hyperkinesia causes the striatial projection neurons to die. the striatum normally inhibits = hypermovement.
-huntington’s disease
chorea
cause?
involuntary, quick, jerky, irregular movements
-caused by atrophy of putamen
hemiballism
what is the cause?
repetitive, but constantly varying, involuntary movement of limbs.
-decreased activity of the subthalamic nucleus = not able to control/ turn off movement
atrophy of the caudate causes
dementia
huntington’s disease is caused by
decreased striatal output leads to decreased inhibition of GPE - increased inhibition of subthalamic nucleus = small signal from STN to the GPI/SNr = small inhibitory signal sent to thalamus = hyperkinesis
hypokinesia
ex
overall decrease in body movements
-parkinson’s disease
bradykinesia
slowness in the execution of a movement
=latin=slow movement
dyskinesia
involuntary muscle movements, tremor to uncontrollable movements of extremities
latin = abnormal morment
akinesia
inability to initiate movement
-latin = without movement
in parkinson’s disease, what area is lost?
chemically what happens ?
loss of substantia nigra pars compacta = decreased dopaminergic output = deceased inhibition of GPe = inhibition of thalamus = hypokinesia
if someone has a tremor in the right thumb, there would be a neuronal loss where?
neuronal loss in the left substantia nigra
symptoms of parkinson’s disease?
bradykinesia, maskied state, tremor at rest, posture and gait
what part of the substantia nigra contains the melanin pigments?
the pars compacts
-dopaminergic- loss during parkinson’s disease
what part of the substantia nigra is the output of the basal ganglia?
pars reticulata
-developmentally related to the globus pallidus internal segment
spinal cord termination
conus medularis
two components of the extrapyramidal system?
- cerebellum
2. basal ganglia
Spasticity= Upper or lower motor neuron sign?
upper motor neuron
are pathologic reflexes present in Upper or lower motor neuron?
pathologic reflexes in upper motor neurons
no pathological reflexes in lower motor neurons
is there muscular atrophy in Upper or lower motor neurons?
- no muscular atrophy in upper motor neurons- bc still active
- prominent muscular atrophy in lower motor neurons
how to tell between Upper or lower motor neuron problem when looking at paralysis of muscles?
- upper motor neurons have entire limb/ side of body affected
- lower motor neurons only have a discrete area
flaccidity= Upper or lower motor neuron sign?
lower motor neuron - b/c not active = atrophy
deep tendon reflexes of Upper or lower motor neuron sign?
hyperactive in upper motor neurons
absent/ hypoactive in lower motor neurons
Upper or lower motor neuron are present where?
upper - cerebral cortex
lower- brainstem / spinal cord
what part of the spinal cord as large ventral horns?
cervical spinal cord and lumbar spinal cord
what part of spinal cord has small ventral horns?
thorasic spinal cord
What ares of the spinal cord has lateral horns?
thorasic spinal cord
a loss of balance due to tripping while walking would be due to what?
vestibulospinal tract (extrapyramidal)
what does the vestibulospinal tract do?
what system is it a part of?
supports posture, balance, controls head movements
extrapyramidal system
where does the tectospinal tract originate and terminate?
origin: midbrain tectum (superior colliculus)
terminate: spinal cord
tectospinal tract modulates?
reflex postural movements in the head from visual input
does the tectospinal tract decussate?if so where?
decussates in midbrain right way in superior colliculi
what system is the rubrospinal tract a part of?
extrapyramidal system
where does the rubrospinal tract originate?
red nucleus (midbrain)
does the rubrospinal tract decussate? if so where?
midbrain
what is the function of the rubrospinal tract?
cerebellar inputs: performs planned movements - alternative to corticospinal tract
the neuromuscular junction involves what type of motor neurons?
lower motor neurons
What is the neuromuscular junction?
releases what?
what can affect here?
- synaptic connection from the nervous system to muscle.
- This action potential triggers a release of calcium. Docking and then a release of Ach vesicles.
- neurotoxins affect here
what is the order of 1-4 of the motor system hierarchy?
- reflex arc
- pyramidal system
- basal ganglion
- cerebellum
-basal ganglia and cerebellum = extrapyramidal
the rest of the CNS exists to
modify reflex arcs
the motor cortex controls mostly what side?
contralateral side
A clinically important point is that the lower motor neurons of the brain stem receive __________ corticobulbar input . Therefore, unilateral corticobulbar tract lesions usually
produce ______________________________,
- bilateral corticobulbar input
- no clinical effect on head and neck muscles with two exceptions: 1. facial nucleus and 2. hypoglossus nucleus
Facial nucleus (VII): The neurons that innervate the muscles of the lower face (below the forehead) receive mainly \_\_\_\_\_\_\_ from the opposite motor cortex. Therefore, a stroke or other lesion involving the left motor cortex or internal capsule causes weakness of the\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ .
- crossed input
- lesion of left motor cortex = weakness of right facial muscles below the forehead, but the patient can still wrinkle her right forehead.
Hypoglossal nucleus (XII): The neurons that innervate the genioglossus muscle receive mainly \_\_\_\_\_\_\_\_from the opposite motor cortex. Therefore, a stroke or other lesion involving the left motor cortex or internal capsule causes \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. When the patient protrudes his tongue, the normal left genioglossus muscle pushes the tongue to the right. However, this deficit is generally transient, lasting a few days.
- crossed input
- lesion involving the left motor cortex or internal capsule causes = weakness of the right genioglossus muscle
A lesion involving all of the corticospinal and corticobulbar fibers from the left cerebral cortex produces……
- Right hemiparesis (weakness of the right upper and lower limbs).
- Weakness of the right face below the forehead.
- Deviation of the tongue to the right upon protrusion (transient).
Pyramidal cells are the ________ neurons of the
cortex.
output
where do corticospinal fibers terminate?
ventral horn on lower motor neurons (alpha)
lower motor neurons of the brain stem receive
_________corticobulbar input.
bilateral
base of caudate head and ventral putamen =
ventral pallidum
putamen + globus pallidus =
lenticular nucleus
caudate + putamen =
striatum
corticospinal tract travels through the ________ of the midbrain
crus cerebri (peduncle)
corticospinal tract travels through the _______ of the medulla
pyramids
in the corticospinal tract - do the axons decussate and if so where?
pyramids of the medulla
corticospinal tract- in the pons axons are located in the ______-
pons proper
primary cells of the corticospinal tract are located _______
frontal and parietal cortex
clinically, the axons of the corticospinal tract are called
upper motor neurons
upper motor nuerons terminate on ________ in the ________
lower motor neurons
ventral horn
