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Quiz 2 - Neuroscience > Descending systems > Flashcards

Descending systems Flashcards

1
Q

What are the functions of the descending tracts?

A
  1. Control of spinal motor neurons
  2. Autonomic functions
  3. Modification of sensory transmission
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2
Q

What are the two ways in which descending motor tracts influence motor neurons?

A
  1. Directly affecting alpha motor neurons
  2. Activating gamma loops
    Both are activated simultaneously with muscle contraction. Gamma loops keep the muscle taut with contraction so that tension can be generated. Resets muscle to a new “set” length
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3
Q

Medial motor systems run in the:

A

ventral/ventrolateral funiculus

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4
Q

Lateral motor systems run in the:

A

lateral funiculus

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5
Q

Purpose of the medial motor system

A

Regulation of interneuron pools to axial and proximal limb muscles

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6
Q

Purpose of the lateral motor system

A

Regulation of interneuron pools going to limb muscles

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7
Q

Name the descending tracts which run in the MLF

A
  1. Tectospinal tract
  2. Medial vestibulospinal tract
  3. Pontine reticulospinal tract
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8
Q

The descending tracts that do run in the MLF are primarily involved in:

A

axial muscle control

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9
Q

Where do the tracts in the MLF end?

A

Upper thoracic regions. Thus, they really only control the head

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10
Q

Where do these tracts in the MLF enter the spinal cord?

A

anterior funiculus

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11
Q

What is the tectospinal tract responsible for?

A

Reflex head and neck movements to visual and auditory stimuli

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12
Q

What is the purpose of the medial vestibulospinal tract?

A

Reflex adjustment of head position to vestibular stimuli

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13
Q

What is the purpose of the reticulospinal tract?

A

Promotes head movement to follow eye movement.

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14
Q

What are the other medial motor tracts?

A

Lateral vestibulospinal tract

Medullary reticulospinal tract

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15
Q

What is the function of the lateral vestibulospinal tract?

A

Powerfully excites extensor motor neurons. Also, vestibular righting reflexes.

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16
Q

What does the medullary reticulospinal tract do?

A

Activates inhibitory interneurons in the spinal cord. Helps control gross movements and muscle tone through gamma motor neuron activity.

17
Q

What are the main descending tracts running in the lateral funiculus? What do they control?

A

rubrospinal and corticospinal tracts–limb movements

18
Q

Initiation of movement shows activity first in which cortex? And then secondarily in which cortex?

A 
premotor cortex (including supplementary motor area (SMA))
then Primary motor cortex
19
Q

The rubrospinal tract, as part of the lateral motor system, has what function?

A

Controls movement of proximal limb flexor muscles

20
Q

Where does the rubrospinal tract arise from?

A

Red nucleus in the superior colliculus

21
Q

Which spinal levels can the rubrospinal tract access?

A

All spinal levels

22
Q

What is the function of the corticospinal system, as part of the lateral motor system?

A

Voluntary command for movement

Regulation of sensory transmission

23
Q

What is the function of the corticobulbar system?

A

Voluntary movement of head and face
Sensory transmission nuclei
Project to pons for relaying information to cerebellum
Activates brainstem nuclei involved in movement

24
Q

The corticospinal tract is the most important of the motor tracts. Describe its pathway.

A

Arises from the precentral gyrus of the motor cortex (BETZ cells–pyramidal neurons)

  • Axons travel along the posterior limb of internal capsule
  • Enter the cerebral peduncles of midbrain
  • Run through basal pons
  • Comprise the pyramids of the medulla
25
Q

What do motor cortex neurons control?

A

Direction of movement, not a specific muscle

26
Q

If the patient is unable to INITIATE movement, where might he have a brain lesion?

A

supplementary motor area

27
Q

Which motor neuron fibers are located at the genu of the internal capsule?

A

Fibers controlling the head muscles

28
Q

Where do the corticospinal tract fibers cross?

A

90% cross at the caudal medulla

10% do not cross at all

29
Q

What do the corticospinal tract fibers do if they decussate?

A

They control interneurons to control finger movements and distal limbs. Some control limb motor neurons. They travel in the lateral funiculis

30
Q

What do the corticospinal tract fibers that DO NOT decussate do?

A

Descend in the anterior funiculus and innervate crude movements of the trunk/limb girdles. Inhibits reflexes within the spinal cord

31
Q

The corticobulbar tract controls what?

A

Facial movements

32
Q

What innervates the upper facial muscles? The lower facial muscles?

A

Upper facial muscles are innervated by corticobulbar tracts bilaterally, from both hemispheres.

The lower face is innervated by the contralateral corticobulbar tract. These two tracts join together as the facial nerve when it leaves the facial nucleus of the pons. Note that an exclusive upper facial motor defect (inability to raise the eyebrows) is more serious than full facial paralysis because it is a problem with the contralateral cerebral cortex.

33
Q

Aside from controlling facial muscles, what else do corticobulbar tracts do?

A

Pontine nuclei–relay to cerebellum
Sensory nuclei–modification of sensory info
Reticular formation–afferent muscle tone and autonomic responses
Brain stem–descending motor tracts

34
Q

What do indirect corticospinal projections do?

A

Anticipatory maintenance of body posture

35
Q

What will you observe with a corticospinal tract lesion?

A

Weakness in contralateral movements in distal muscles (assuming lesion is above the pyramidal decussation). This causes hyperactive withdrawal reflexes (Babinski) Also spasticity

36
Q

You observe muscle atrophy, faccidity, decreased reflexes and a normal plantar reflex. Where is the lesion within the corticospinal tract?

A

It’s located within the motor neuron itself, distal to the corticospinal tract

37
Q

You observe little atrophy, spasticity, increased reflexes and a babinski reflex. Where is the lesion within the corticospinal tract?

A

Upper motor neuron weakness in the corticospinal tract.

38
Q

What is decorticate posturing? What does this mean if it is observed in a comatose patient?

A

Noxious stimulus causing extension of the legs and flexion of the arms. Indicates a lesion above the red nucleus

39
Q

What is decerebrate posturing? What does it mean if you observe this in a comatose patient?

A

Extension of arms and legs in response to a noxious stimulus. Indicates a lesion between the red nucleus and vestibular nuclei

Quiz 2 - Neuroscience (11 decks)

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