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Neuro Exam II > Corticobulbospinal tracts - SRS > Flashcards

Corticobulbospinal tracts - SRS Flashcards

1
Q

In the spinal cord and brainstem, lower motor neurons directly innervate what?

A

Muscle

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2
Q

What are lower motor neurons controlled by?

A
  1. Local circuits within the spinal cord and brainstem
  2. Upper motor neurons
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3
Q

What regulates upper motor neurons?

A

Basal ganglia and cerebellum

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4
Q

Where are lower motor neuron cell bodies located?

A

Ventral horn of the spinal cord

Brainstem motor nuclei

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5
Q

What are the two types of lower motor neurons that innervate skeletal muscle?

A

Alpha and Gamma

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6
Q

Where are upper motor neuron cell bodies located?

A
  1. -Cortex (Corticospinal)
    1. Cortex (Corticobulbar)
  2. –Vestibular nuclei (Vestibulospinal)
  3. –Superior colliculus (Tectospinal)
  4. –Reticular formation (Reticulospinal)
  5. –Red nucleus (Rubrospinal)
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7
Q

Where do interneurons for axial structures located?

Do they have many collaterals?

Unilateral or bilateral?

A

Medial, and bilateral.

Possess many collaterals

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8
Q

Where do interneurons for Limb structures located?

Unilateral or bilateral?

Do they have many collaterals?

A

More lateral, are unilateral and have fewer collaterals.

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9
Q

A single alpha motor neuron and all the muscle fibers it innervates = ?

A

Motor unit

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10
Q

How do we change the amount of force produced by a muscle?

A

Increase or decrease the amount of motor units recruited.

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11
Q

Identify the blanked out structures

A
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12
Q

The neuromuscular junction/motor end plate is analagous to a?

A

Synapse

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13
Q

Alpha Motor neurons from the spinal cord innervate muscles involved in excitation-contraction coupling. Characterize these fibers by speed and structure.

A

Fast

Myelinated

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14
Q

In excitation-contraction coupling, what NT is released by the alpha motor neuron?

What receptors does it bind?

What type of receptors are these?

A
  2. releases acetylcholine
  3. Binds to nicotinic receptors
  4. these are ligand-gated Na+ channels
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15
Q

What are the junctional folds of the neuromuscular junction often continuous?

A

T-Tubules

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16
Q

Motor units differ in the types of muscle fibers they innervate. What are the three types we covered?

A

Slow motor units

Fast fatigable motor units

Fast Fatigue-resistant motor units

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17
Q

Descrime the muscle fibers of slow motor units.

A

–Smaller, red muscle fibers (myoglobin, mitochrondria, capillary beds)

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18
Q

What size are the slow motor unit alpha-motor unit neurons?

What level of force do these generate?

How fatigable are they?

A

–Smaller Alpha-motor neurons
–Small force
–Resistant to fatigue

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19
Q

What are fatigue resistant slow motor units imporant for?

Describe their threshold for activation.

A
  • Important for sustained muscle contraction (eg. Regulating posture)
  • Lowest thresholds for activation = recruited first
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20
Q

Describe the size and color of Fast fatigable motor unit fibers.

What size alpha motor neurons are we dealing with here?

What is the force like?

Fatiguability?

A

–Larger, pale muscle fibers (few mitochondria)
–Larger Alpha motor neurons
–Large force
–Easily fatigued

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21
Q

In what manner of activity are fast fatigable motor units most useful?

A

•Brief exertions that require large forces (eg. jumping)

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22
Q

Where do fast fatigue resistance motor units fall on the spectrum of muscle fiber types?

What else are they known as?

A

–Between slow motor units and fast fatigable motor units (aka intermediate motor units)

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23
Q

As the synaptic activity driving motor neurons increases, in what order do we recruit the motor neuron types?

A
  1. slow motor neurons
  2. fast, fatigue-resistant motor neurons
  3. fast fatigable motor neurons
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24
Q

What is muscle tone?

A

The resting level of tension in a muscle

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25
Q

What does muscle tone enable us to do?

A

•Allows muscle to make an optimal response to voluntary or reflexive movement by keeping them in a state of readiness to resist stretch

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26
Q

What does denervation do to muscle?

A

Causes rapid atrophy

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27
Q

When muscle fiber degenerate, they are replaced by fatty and fibrous tissue, leading to loss of contractile proteins in muscle cells. What can this fibrous tissue cause?

A

Contracture

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28
Q

Why do muscles atrophy in the elderly?

A

_Loss of motor neurons _ due to vascular disease and poor nutrition.

29
Q

When motor neurons are lost, motor end plates are innervated by collaterals of adjacent motor neurons, leading to an abnormal EMG signature know as?

A

Giant motor units

30
Q

What are typical signs of lower motor neuron damage?

A

Paralysis or paresis

areflexia

atrophy

fibrillations

fasciculations

31
Q

What are fibrillations? What are they due to?

A

–Rapid twitching due to change in muscle fiber excitability *denotes pathology*

32
Q

What are fasciculations?

A

–Local, small twitch due to alpha motor neuron damage

33
Q

What pathways for upper motor control of lower motor neurons are extrapyramidal? (4)

A

–Vestibular (vestibulospinal)
–Reticular (reticulospinal)
–Red nucleus (rubrospinal)
–Superior colliculus (tectospinal)

34
Q

What pathways for upper motor neuron control of LMN’s is pyramidal?

A

–Lateral corticospinal
–Ventral corticospinal
–Corticobulbar

35
Q

From what nuclei does the vestibulo spinal tract arise?

A

LAteral or medial vestibular nuclei

36
Q

What does the lateral vestibular nuclei command?

A

**Ipsilateral: **posture, including extensors

37
Q

What does the medial vestibular nuclei command?

A

**Bilateral: **head position stability

38
Q

Identify blanked structures

A
39
Q

Where does the tectospinal tract arise?

A

Superior colliculus

40
Q

What does the tectospinal tract influence?

A

Musculaturs of neck and eyes

Postural reflexes to alarming visual stimuli and some auditory stimuli

41
Q

Identify

A
42
Q

The reticulospinal tract arises from different brainstem levels. Does it decussate?

What does it control?

A

Does not decussate

Affects axial and postural muscles, and provides secondary control when CST is dysfunctional

43
Q

What is the reticulospinal tract largely controlled by?

A

Cortical motor centers

44
Q

Identify

A
45
Q

What does the rubrospinal tract innervate? What does it do?

A

Innervates spinal cord through thoracic levels.

It is a laterally based tract possibly involved in flexor muscles of the arm. Not entirely sure what it does in humans.

46
Q

Ident

A
47
Q

What organizes the movement of individual muscles?

A

Motor homunculus in the primary motor cortex

48
Q

What organizes the movement of groups of muscles?

A

Motor homunculi in premotor and supplementary motor cortices

49
Q

Where are Betz cells found? In what layer are they found?

A

Primary motor cortex

Layer V

50
Q

What do Betz cells project through?

A
  • Project through posterior limb of internal capsule
  • Through medullary pyramids
51
Q

What does the pyramidal tract provide collaterals to?

A
  1. Reticular formation
  2. Trigeminal
  3. Facial
  4. Nucleus ambiguus
52
Q

Describe the decussation of the pyramidal tract.

A

80% at the caudal medulla

20% continue ipsilateral

53
Q

What tract do the decussating fibers of the pyramidal tract take after decussation?

What does this innervate?

A
  • “Lateral corticospinal tract”
  • Limbs, digits (stuff needing fine motor control)
54
Q

What path do the 20% of pyramidal tract fibers take?

What do they go to?

They have a second chance at decussating, where do they get this opportunity?

A
  • “anterior or ventral corticospinal tract”
  • Axial muscles
  • Some of these will decussate in the anterior white commissure, some won’t at all
55
Q

Ident

A
56
Q

Ident

A
57
Q

For bronchiomeric muscles, specifically facial expression above the eyes, what do lesions of the cortex produce?

A

Bilateral deficiencies (but minor)

58
Q

For bronchiomeric muscles, specifically facial expression above the eyes, what do lesions of the nucleus produce?

A

Ipsilateral Deficiency

59
Q

For muscles of facial expression below the eyes, muscles of mastication and the tongue, what does a lesion of the cortex cause?

A

Contralateral deficiency

60
Q

For muscles of facial expression below the eyes, muscles of mastication and the tongue, what does a lesion of the nucleus cause?

A

Ipsilateral deficiency

61
Q

Identify these locations

A
62
Q

Identify this location

A
63
Q

What doe a + Babinski’s sign in adults indicate?

A

If toes point upward instead of downward due to loss of upper motor neuron control

64
Q

What is spasticity a sign of?

A

–Corticospinal influences probably are somewhat inhibitory to the brainstem control of postural muscles—relaxes them a bit.

65
Q

What can cause loss of fine motor control?

A

Corticospinal damage

66
Q

ALS arises due to degeneration of what?

A

Corticospinal and LMN

67
Q

What is the average time to fatality post ALS diagnosis?

A

5 yrs

68
Q
A

Neuro Exam II (13 decks)

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