Kenyon: Motor Neurons II

Question 1

The lateral corticospinal tract projects from upper motor neurons in the cerebral cortex to where?

Answer 1

lower motor neurons in the lateral ventral horn

Question 2

Lower motor neurons with cell bodies located laterally project to what muscles?

Answer 2

limb muscles

Question 3

Lower motor neurons with cell bodies located medially project to what muscles?

Answer 3

axial (postural) muscles

Question 4

What are two bulbospinal tracts that we should be concerned about?

Answer 4

vestibulospinal

reticulospinal

Question 5

Where do upper motor neurons in the brainstem project to via the vestibulospinal and reticulospinal tracts?

Answer 5

to lower motor neurons in the medial ventral horn *to supply axial and proximal muscles for posture and balance

Question 6

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.

Answer 6

cerebral cortex –> cerebral peduncles –> pyramidal decussation –> spinal cord

Question 7

Local circuit neurons controlling posture are located (blank), and projections are (blank)

Answer 7

medially; long *over many segments and to both sides of the cord

Question 8

What do medial local circuit neurons do?

Answer 8

coordinate many axial muscles on both sides of the body

*often cross over

Question 9

Local circuit neurons controlling limbs are located (blank), and projections are (blank)

Answer 9

laterally; short *extend only a few segments

Question 10

Do local circuit neurons controlling limbs usually cross?

Answer 10

no! rarely cross to contralateral side

*independent control of a few muscles

Question 11

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.

Answer 11

brainstem; corticobulbar; spinal cord; corticospinal

Question 12

What kind of info does the lateral corticospinal tract carry? Where will the info ultimately go to?

Answer 12

info from motor cortex for limbs and hands;

to lateral and intermediate regions of the spinal cord

Question 13

The lateral corticospinal tract sends branches where?

Answer 13

dorsal column nuclei (gracile and cuneate)

Question 14

Does the lateral corticospinal tract cross at the pyramidal decussation?

Answer 14

**yes

Question 15

What kind of information does the ventral corticospinal tract carry?

Answer 15

info from cortex for hip, trunk, shoulder, elbow, and neck; to medial regions of spinal cord on both sides

Question 16

Does the ventral corticospinal tract cross at the pyramidal decussation?

Answer 16

**does not cross at pyramidal decussation, but may cross in lower regions of the spinal cord

Question 17

Where else can upper motor neurons contributing to ventral corticospinal tract send axons to?

Answer 17

reticular formation *ex: corticobulbar

Question 18

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?

Answer 18

coordination of postural movements

Question 19

Where are the cell bodies of lower motor neurons controlling the superior/inferior facial muscles located?

Answer 19

in the ipsilateral facial nerve nucleus

Question 20

Upper motor neurons originating in (blank) premotor cortex project to lower motor neurons that control INFERIOR facial muscles.

Answer 20

CONTRALATERAL

Question 21

Upper motor neurons originating in (blank) and (blank) cingulate gyrus project to lower motor neurons controlling SUPERIOR facial muscles.

Answer 21

CONTRALATERAL and IPSILATERAL

Question 22

So how does upper motor neuron innervation of superior and inferior facial muscles differ?

Answer 22

superior facial muscles receive input from contralateral and ipsilateral side, while inferior facial muscles only receive input from contralateral side

Question 23

What would a lower motor neuron lesion cause in the face? What would an upper motor lesion cause in the face?

Answer 23

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)

Question 24

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…

Answer 24

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)

Question 25

If you lose your corticobulbar tract or cingulate gyrus (ex: anterior cerebral artery), what kind of weakness will be observed in the face?

Answer 25

weakness/paralysis of inferior facial muscles | *upper motor neurons in ipsilateral cingulate gyrus maintain function of superior facial muscles

Question 26

What is the source of the lateral corticospinal tract? Where does this tract cross? Where does it project to?

Answer 26

motor cortex for limbs and hands; pyramids; lateral and intermediate regions of the spinal cord

Question 27

What is the source of the ventral corticospinal tract? Where does it cross? Where does it project to?

Answer 27

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)

Question 28

Where does the corticobulbar tract originate? Does it cross? Where does it project to?

Answer 28

originates in the motor cortex for face; some cross, some do not; project to cranial nerve nuclei

Question 29

What does the vestibular nucleus receive inputs from? What tract does it give output to? Where does it project to? What is the function?

Answer 29

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

Question 30

What does the reticular formation receive inputs from? What tract does it give outputs to? Where does it project to? What is the function?

Answer 30

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

Question 31

The vestibulospinal tract is from the (blank) to the (blank)

Answer 31

vestibular nucleus; medial and lateral regions of the spinal cord

Question 32

The vestibulospinal tract receives input from (blank)

Answer 32

semicircular canals

Question 33

The vestibulospinal tract controls what?

Answer 33

axial and proximal limb muscles in posture and balance | VOR movements while head is moving

Question 34

The reticulospinal tract is from the (blank) to the (blank)

Answer 34

pontine and medullary reticular formation; medial spinal cord

Question 35

What does the reticulospinal tract receive input from?

Answer 35

primary motor cortex | *via ventral coticospinal tract

Question 36

Where does the reticulospinal tract project to?

Answer 36

medial spinal cord to control axial and proximal limb muscles

Question 37

Where do upper motor neurons in the superior colliculus project to?

Answer 37

reticular formation then to medial region of spinal cord and gaze centers (to coordinate saccades)

Question 38

What do the inferior colliculi receive inputs from?

Answer 38

``` upper body proprioceptors retina auditory olfaction from cortex for eye position ```

Question 39

What does the superior colliculus pathway function in?

Answer 39

orienting the head saccades tomato-somatic reflex

Question 40

List the flow from upper motor neurons to skeletal muscles

Answer 40

Upper motor neurons act on local circuit neurons that act on lower motor neurons that activate skeletal muscle

Question 41

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

Answer 41

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

Question 42

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?

Answer 42

superior colliculus | reticular formation

Question 43

In complex voluntary movements, activity here sets up an intent to make a movement, selects appropriate movements, responds to external cues

Answer 43

lateral premotor cortex | ex: can respond to a tiger leaping through the door

Question 44

In complex voluntary movements, activity here sets up an intent to make an internally generated movement

Answer 44

medial premotor cortex | ex: I am going to touch my nose

Question 45

What are early responses to upper motor neuron syndrome?

Answer 45

spinal shock flaccidity on contralateral side loss of limb reflexes

Question 46

In upper motor neuron syndrome, is posture affected?

Answer 46

postural muscles may remain functional due to local circuit neurons that cross over

Question 47

What are some stable (long term) responses to upper motor neuron syndrome?

Answer 47

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

Question 48

3 signs of upper motor neuron syndrome

Answer 48

increased tone hyperactive deep reflexes clonus

Question 49

Symptoms of lower motor neuron syndrome?

Answer 49

``` weakness/paralysis decreased superficial reflexes hypoactive deep reflexes decreased tone fasciculations severe muscle atrophy ```