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Neuro Quiz 2_yl > Descending motor system > Flashcards

Descending motor system Flashcards

1
Q

List the functions of the descending tract/ (4)

A
  • produce movement
  • modify tone
  • control autonomic function
  • regulate sensory transmission
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2
Q

Where do most descending tracts synapse?

A

interneurons; small part directly on motor neuron (alpha motor neurons, esp corticospinal tract predominately)

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3
Q

What are the three tracts in MLF (medial longitudinal funiculus)?

A

-include the tectospinal, medical vestibulospinal, and ponine reticulospinal tracts

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4
Q

What does medial motor system include?

A

Descending MLF, Lateral vestibulospinal, and medullary reticulospinal tract.

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5
Q

What are the common characteristics of MLF?

A
  • run in anterior funiculus
  • all end above upper thoracic cord
  • all terminate on axial motor neurons
  • all terminate bilaterally
  • mainly control axial muscles
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6
Q

What is the function of lateral vestibulospinal tract?

A

facilitating extensor

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7
Q

What is the function of medullary reticulospinal tract?

A

inhibits cord motor neuron excitability

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8
Q

What is the general definition of “corticobulbar” or “corticalspinal”

A

everything from cerebral cortex and going to brain stem or spinal cord.

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9
Q

Need to know the effect of corticobubar tract damage on face, tongue, jaw, and palate movement

A

yes, damage to cortical efferents produce UMN signs

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10
Q

What are the two aspects of UMN (upper motor neuron) signs?

A
  • hyperactive reflexes, spasticity, pathological reflexes (e.g. Babinski)
  • Motor neuron damage (LMN) -decreased tone & reflexes, atrophy
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11
Q

How to tell the difference in gross structure between the cervical and thoracic spinal cord?

A

Since there is not much lateral motor neurons -> thoracic spinal cord has a smaller ventral horn (lower extremities considered axial)

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12
Q

How does the DMT INDIRECTLY affect alpha motor neurons?

A
  1. affect reflex excitability - primarily by affecting interneurons
  2. initiate movement through activation of the gamma loop - activate gamma neurons, producing reflex contraction of muscles to new length “set point”
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13
Q

How do you explain the fact that interneuron to limb muscles have more focused distribution compared to the ones controlling axial muscle motor neurons pools

A

You can control your individual finger - certain dexterity; versus spinal/back/lower extermities muscle turn to move in groups/as a whole

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14
Q

What does “older system’ mean in explaining that there are multiple motor pathway?

A
  • there is a phylogenetic hierarchy (primitive -> sophisticated)
  • more “recent” tracts utilize the “older system”
  • “older system” have more general effects and often influence reflex response
  • “older systems” are primarily directed at postures, tone, and proximal limb or trunk motion.
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15
Q

Compare the differences between medial and lateral motor systems.

A
  • medial motor system run in ventral orventrolateral funiculus, mainly regulate interneurons pools going to axial and proxiamal limb muscles
  • Lateral motor system run in lateral funiculus, regulating the interneurons going to limb muscles.
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16
Q

What about superior colliculus?

A
  • has a precise map of the entire sensory world
  • esp the visual map
  • if stimulate, eyes move immediately
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17
Q

What is the PPRF (paramedial pontine reticular formation)?

A

has to do with horizontal gaze; prevent neck from moving while the eye gaze at somewhere.

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18
Q

What is medial vestibulospinal tract?

A
  • from medial vestibular nucleus
  • runs in the descending MLF
  • reflex adjustment of head position to vestibular stimuli
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19
Q

Tell the pathway of the tectospinal tract.

A
  • Arises from the deep layers of the superior colliculus.
  • Crosses in the midbrain (dorsal tegmental decussation) and descends in the MLF and anterior funiculus to upper thoracic levels.
  • Terminates in the medial part of the intermediate gray
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20
Q

What kind of inputs does superior colliculus receives?

A

receives input from the cortex, visual systems, auditory systems and somatic sensory systems (multisensory).

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21
Q

What is the result of stimulating tectospinal tract?

A

Reflex head & arm movement to stimuli (esp. visual and auditory)

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22
Q

What is (pontine) reticulospinal tracts?

A
  • mostly from pontine lateral gaze center
  • promote head movement to follow eye movement
  • run in MLF
23
Q

What about the other medial motor tract (lateral vestibulospinal tract and medullary reticulospinal tract)?

A
  • run near the cap of the ventral horn
  • extend the length of the spinal cord
  • involved in regulating muscles tone and producing crude movement
24
Q

Give me more details about the lateral vestibulospinal tract.

A
  • from lateral vestibular nucleus
  • runs down the length of the spinal cord in ventral lateral funiculus
  • powerfully excites extensor motor neurons: vestibular righting reflex (in order to maintain balance of the people preventing falls). This should be suppressed in 3-4 months during infant development.
25
Q

What about (medullary) reticulospinal tract?

A
  • predominantly activates inhibitory interneruons in spinal cord
  • activity in this tract can be regulated by corticobular tract: indirect cortico reflex
  • control generalized, gross movements
  • regulate gamma motor neuron activity
  • contains descending autonomic fibers and respiratory control fibers
26
Q

What are the two main lateral motor descening tract?

A

Rubrospinal and corticospinal tract

27
Q

Tell me about the rubrospinl tract.

A
  • arise from the red nucleus of midbrain
  • crosses in the midbrain, at the ventral tegmental decussation
  • descends in the lateral funiculus
  • reaches all spinal leves (esp. cervical)
  • small tracts in humans; in lower animals, important in control of limbs.
  • terminates: intermediate gray matter interneuronsa dn in dorsal horn
28
Q

Where do red nuclues receive input from and what is the result of stimulus transported by rubrospinal tract?

A
  • input from cortex and cerebellum
  • control movements of more proximal limb flexor muslces (crawling)
  • can be an indirect corticospinal tract
29
Q

What is the function of corticospinal system?

A
  • voluntary command for movement

- regulate sensory transmission through dorsal horn

30
Q

What is the function of corticobulbar system?

A
  • affect cranial nerve nuclei -voluntary movement of head and face
  • affect sensory transmission nuclei
  • activate brainstem nuclei involved in movement -indirect corticospinal projection.
  • project to pons for relay to cerebellum
31
Q

If the distal limb function is limited, where do you suspect first?

A

Corticospinal tract

32
Q

Corticospinal Tract

A
  • arise from the motor cortex-precentral gyrus (specifically, from pyramidal neurons -largest ones called “betz” cells)
  • axons transverse the posterior limb of internal capsule
  • enter the cerebral peduncles of midbrain
  • run through the basal pons
  • comprise the pyramids of the medulla
33
Q

Pre-motor cortex is about:

A
  • in front of motor cortex

- lot of planning, synthesis, and patterning of movement

34
Q

supplementary motor area (cortex)

A
  • decision whether to move or not.

- active even if the movement is not executed!

35
Q

What do motor cortical neurons encode during movement initiation?

A

direction of movement, not a specific muscle (compared to anterior horn neurons - going to single muscles)

36
Q

What is damage to the supplementary motor area called? What is the symptom?

A

abulia - difficulty/inability in initiation of movement

37
Q

Where is the internal capsule?

A

Lateral to the thalamus

38
Q

Where are the H,A, L corticofugal fibers?

A

The head (H) fibers are in the genu and the rest are in the posterior limb of the internal capsule (all for voluntary movements!)

39
Q

Talk about the crossing of the corticospinal tract

A

90 percent of fibers cross at the lowest part of the medulla and 10% uncrossed

  • crossed fibers make up the lateral corticpinal tract in lateral funiculus; some go directly to motor neurons to limb muscles; particular important in control of independent digits (e.g. in case of massive stroke: can still move axial muscles, but lose voluntary hand function)
  • run in anterior funiculus; go to axial muscles -crude movement
40
Q

Where does the corticospinal tract erminates?

A

in the dorsal horn where the tract may influence sensory transmission and reflexes

41
Q

What is the overall function of the corticospinal tract?

A

Inhibits reflexes at the cord

42
Q

List the function of the corticobulbar tracts (6)

A
  • cranial nerve nuclei (esp. facial)
  • pontine neuclei (replay to cerebellum)
  • indirect corticospinal tracts
  • eye movement control
  • sensory nuclei (regulate transmission)
  • visceral centers (respiration, etc)
43
Q

Described the location of the facial nucleus.

A

From the face part of somatosensory cortx and anterior cingulate

  • crossed projection to the part that innervates the lower face (e.g. tongue muscle)
  • the part innervates the upper face is bilaterally innervated (frown, close eyes,..)
  • cingulate connection involved in producting emotion facial expression
44
Q

Does the upper or lower face muscles produce more delicated movement?

A

Lower

45
Q

What about other tracts strctures in the corticobular tracts?

A
  • pontine neuclei -major target of corticobulbar tract: for relay to cerebellum and comes from all parts of the cortex
  • sensory neuclei: modify sensory transmission
  • Reticular formation: affect muscle tone, autonomic response and level of alertness
  • brains stem areas giving rise to descending motor tracts (e.g red nucleus, reticular formation, superior colliculus)
46
Q

Compare of lesion of premotor cortex and motor cortex

A
  • motor cortex: weakness in general, loss of muscle tone

- premotor cortex: increase reflex

47
Q

What about anticipatory maintenance of body posture?

A

Activity in many supporting and stabilizing muscles is produced by indirectly corticospinal projection
-.e.g. using bicep to full an lever: the stimulus sending to gastrocnemius muscle is prior to that of biceps.

48
Q

What are the clinical aspects o corticospinal tract lesions?

A
  • weakness in contralateral movements (when lesion above the pyramidal decussation)
  • most severe distally, with preservation of axial muscles
  • severe deficits in fine motor control (especially hand) contralaterally
  • hyperactive myotatic and withdrawal reflexes
  • spasticity is common due to lack of inhibition of indirect corticospinal tracts (such as those involving corticoreticular => reticulospinal tracts)
49
Q

Babinski sign

A

on the lateral side of the foot -> normal: toes down; Babinski sign: externsor plantar response -> up and fanning of toes (in pt and infant)

50
Q

Compare the upper versus lower motor neuron weakness

A

Lower motor neuron: ++ atrophy; flaccid, decreased reflexes; no pathological reflexes
Upper motor neuron: little atrophy, spasticity, increased reflexes, and pathological reflexes-Babinski

51
Q

What is lower motor neurons (LMN)?

A

the anterior horn cells (alpha) and its axons

52
Q

What is upper motor neurons (UMN)?

A

descending motor tracts

53
Q

What causes decorticate posturing

A

lesion above the red nucleus

54
Q

What causes the decerebrate posturing

A

lesion between red and vestibular nuclei

Neuro Quiz 2_yl (8 decks)

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