Kenyon: Motor Neurons II Flashcards
The lateral corticospinal tract projects from upper motor neurons in the cerebral cortex to where?
lower motor neurons in the lateral ventral horn
Lower motor neurons with cell bodies located laterally project to what muscles?
limb muscles
Lower motor neurons with cell bodies located medially project to what muscles?
axial (postural) muscles
What are two bulbospinal tracts that we should be concerned about?
vestibulospinal
reticulospinal
Where do upper motor neurons in the brainstem project to via the vestibulospinal and reticulospinal tracts?
to lower motor neurons in the medial ventral horn *to supply axial and proximal muscles for posture and balance
Describe the course of the lateral corticospinal tract as it goes from upper motor neurons in the cortex to lower motor neurons in the lateral ventral horn.
cerebral cortex –> cerebral peduncles –> pyramidal decussation –> spinal cord
Local circuit neurons controlling posture are located (blank), and projections are (blank)
medially; long *over many segments and to both sides of the cord
What do medial local circuit neurons do?
coordinate many axial muscles on both sides of the body
*often cross over
Local circuit neurons controlling limbs are located (blank), and projections are (blank)
laterally; short *extend only a few segments
Do local circuit neurons controlling limbs usually cross?
no! rarely cross to contralateral side
*independent control of a few muscles
The lower motor neurons controlling muscles of the face are in the (blank). They receive input from upper motor neurons via (blank) tract. Lower motor neurons controlling the muscles in the rest of the body are in the (blank). They receive input from upper motor neurons via the (blank) tract.
brainstem; corticobulbar; spinal cord; corticospinal
What kind of info does the lateral corticospinal tract carry? Where will the info ultimately go to?
info from motor cortex for limbs and hands;
to lateral and intermediate regions of the spinal cord
The lateral corticospinal tract sends branches where?
dorsal column nuclei (gracile and cuneate)
Does the lateral corticospinal tract cross at the pyramidal decussation?
**yes
What kind of information does the ventral corticospinal tract carry?
info from cortex for hip, trunk, shoulder, elbow, and neck; to medial regions of spinal cord on both sides
Does the ventral corticospinal tract cross at the pyramidal decussation?
**does not cross at pyramidal decussation, but may cross in lower regions of the spinal cord
Where else can upper motor neurons contributing to ventral corticospinal tract send axons to?
reticular formation *ex: corticobulbar
Upper motor neurons in the primary motor cortex and premotor cortex can also send projections to the reticular formation via the indirect pathway. What does activity in this pathway allow for?
coordination of postural movements
Where are the cell bodies of lower motor neurons controlling the superior/inferior facial muscles located?
in the ipsilateral facial nerve nucleus
Upper motor neurons originating in (blank) premotor cortex project to lower motor neurons that control INFERIOR facial muscles.
CONTRALATERAL
Upper motor neurons originating in (blank) and (blank) cingulate gyrus project to lower motor neurons controlling SUPERIOR facial muscles.
CONTRALATERAL and IPSILATERAL
So how does upper motor neuron innervation of superior and inferior facial muscles differ?
superior facial muscles receive input from contralateral and ipsilateral side, while inferior facial muscles only receive input from contralateral side
What would a lower motor neuron lesion cause in the face? What would an upper motor lesion cause in the face?
muscle weakness on entire contralateral side of the face (inferior and superior muscles weak);
muscle weakness in inferior contralateral quadrant of the face (still have superior muscles intact)
Loss of lower motor neurons to the face results in…
Loss of primary or premotor (upper motor) neurons (ex: middle cerebral artery) to the face results in…
weakness or paralysis of superior and inferior facial muscles; weakness of inferior facial muscles (superior facial muscles maintained by upper motor neurons in cingulate gyrus)
If you lose your corticobulbar tract or cingulate gyrus (ex: anterior cerebral artery), what kind of weakness will be observed in the face?
weakness/paralysis of inferior facial muscles
*upper motor neurons in ipsilateral cingulate gyrus maintain function of superior facial muscles
What is the source of the lateral corticospinal tract? Where does this tract cross? Where does it project to?
motor cortex for limbs and hands; pyramids; lateral and intermediate regions of the spinal cord
What is the source of the ventral corticospinal tract? Where does it cross? Where does it project to?
motor cortex for hip, trunk, shoulder, elbow, neck; not at pyramids, some crossing in spinal cord lower down; to medial region of spinal cord (may project to reticular formation)
Where does the corticobulbar tract originate? Does it cross? Where does it project to?
originates in the motor cortex for face; some cross, some do not; project to cranial nerve nuclei
What does the vestibular nucleus receive inputs from? What tract does it give output to? Where does it project to? What is the function?
semicircular canals; vestibulospinal tract; projects to medial and lateral regions of the spinal cord; functions in controlling axial and proximal limb muscles for posture and balance, as well as VOR reflex for eye movements while the head is moving
What does the reticular formation receive inputs from? What tract does it give outputs to? Where does it project to? What is the function?
input from primary motor cortex from ventralcorticospinal or corticobulbar tracts; output is reticulospinal tract; projects to medial region of spinal cord; controls axial and proximal limb muscles for posture and balance
The vestibulospinal tract is from the (blank) to the (blank)
vestibular nucleus; medial and lateral regions of the spinal cord
The vestibulospinal tract receives input from (blank)
semicircular canals
The vestibulospinal tract controls what?
axial and proximal limb muscles in posture and balance
VOR movements while head is moving
The reticulospinal tract is from the (blank) to the (blank)
pontine and medullary reticular formation; medial spinal cord
What does the reticulospinal tract receive input from?
primary motor cortex
*via ventral coticospinal tract
Where does the reticulospinal tract project to?
medial spinal cord to control axial and proximal limb muscles
Where do upper motor neurons in the superior colliculus project to?
reticular formation then to medial region of spinal cord and gaze centers (to coordinate saccades)
What do the inferior colliculi receive inputs from?
upper body proprioceptors retina auditory olfaction from cortex for eye position
What does the superior colliculus pathway function in?
orienting the head
saccades
tomato-somatic reflex
List the flow from upper motor neurons to skeletal muscles
Upper motor neurons act on local circuit neurons that act on lower motor neurons that activate skeletal muscle
When you go to perform a voluntary movement, like pulling on a handle, your biceps are not the first muscles to be activated. Rather, muscles in your legs are activated to prevent you from falling over. What is happening
A central command (pull on handle) produces a direct action (limb movement) and an indirect action (postural adjustment)
- *feedforward for anticipated postural instability
- *feedback for unanticipated postural instability
When performing complex voluntary movements, direct and indirect pathways both link the motor cortex with the spinal cord. Direct pathways go straight from cortex to spinal cord. Where do indirect pathways project to?
superior colliculus
reticular formation
In complex voluntary movements, activity here sets up an intent to make a movement, selects appropriate movements, responds to external cues
lateral premotor cortex
ex: can respond to a tiger leaping through the door
In complex voluntary movements, activity here sets up an intent to make an internally generated movement
medial premotor cortex
ex: I am going to touch my nose
What are early responses to upper motor neuron syndrome?
spinal shock
flaccidity on contralateral side
loss of limb reflexes
In upper motor neuron syndrome, is posture affected?
postural muscles may remain functional due to local circuit neurons that cross over
What are some stable (long term) responses to upper motor neuron syndrome?
Babinski sign (toes curl away) *present in infants and in injury
Spasticity *increased muscle tone
Hyperactive stretch reflexes *less gamma inhibition
Hyporeflexia of superficial reflexes *corneal reflexes, cremasteric reflex
Loss of fine voluntary movements
3 signs of upper motor neuron syndrome
increased tone
hyperactive deep reflexes
clonus
Symptoms of lower motor neuron syndrome?
weakness/paralysis decreased superficial reflexes hypoactive deep reflexes decreased tone fasciculations severe muscle atrophy
