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Neuroanatomy Exam II > Corticospinal and Corticobulbar pathways > Flashcards

Corticospinal and Corticobulbar pathways Flashcards

1
Q

Where do corticospinal and corticobulbar pathways begin and end?

A

Begin from neurons in the cerebral cortex and end on lower motor neurons in the spinal cord and brainstem

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2
Q

What do the corticospinal and corticobulbar pathway neurons serve as and what do their axons form?

A

Neurons serve as upper motor neurons and their axons form major descending motor control pathways that modify motor activity

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3
Q

As the corticospinal and some of the corticobulbar fibers descend through the CNS what structure do they traverse?

A

Medullary pyramids

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4
Q

What are the corticospinal and corticobulbar pathways that traverse the medullary pyramids known as?

A

Pyramidal system

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5
Q

What are the descending motor pathways that do not traverse the pyramids known as?

A

Extrapyramidal system

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6
Q

What are some examples of extrapyramidal system?

A

Vestibulospinal tract
Medial longitudinal fasciculous
Tectospinal and tectobulbar tracts

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7
Q

Where do corticospinal and corticobulbar tracts originate?

A

From neurons in frontal and parietal lobes

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8
Q

Which part of the frontal lobe do corticospinal and corticobulbar originate from?

A

Precentral gyrus and anterior paracentral lobule

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9
Q

What percent of pyramidal fibers are contributed by the frontal lobe?

A

30%

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10
Q

What neurons do pyramidal fibers of corticospinal and corticobulbar in the frontal lobe originate from?

A

From giant pyramidal neurons known as Betz cells

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11
Q

What brodmann map area is associated with the frontal lobe where pyramidal fibers originate from?

A

4

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12
Q

What is the frontal lobe where corticospinal and corticobulbar originate from known as?

A

Primary motor cortex (M1)

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13
Q

What does the primary motor cortex do?

A

Muscle contractions on the contralateral body and muscle contractions are single muscles or muscles that move a single joint or digit

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14
Q

Is the Primary motor cortex somatopically organized?

A

Motor homonculus

- similar to sensory homonculous of primary somatosensory cortex

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15
Q

What is the premotor and supplementary motor areas (of the frontal lobe) correspond anatomically with?

A

Premotor = superior and middle frontal gyrus

Supplemental motor area = medial frontal gyrus

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16
Q

What are the Brodmann map area for the premotor and supplementary motor areas?

A

6 and some of 8

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17
Q

What percent of the pyramidal fibers originate in the premotor and supplementary motor areas?

A

30%

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18
Q

What do premotor and supplementary motor areas do?

A

1) contraction on contralateral side of body (synergistic or patterned movements
2) programming of skilled movements (without thought required)
3) supplementory area - plays a role in planning for execution of movement

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19
Q

What areas of the parietal lobe are included in the pyramidal system?

A

Postcentral gyrus, posterior paracentral lobule and superior parietal lobule

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20
Q

What percent of the pyramidal fibers originate in the parietal lobe that are included in the pyramidal system?

A

about 40%

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21
Q

True or False: all descending fibers that originate from the parietal lobe that includes the pyramidal system are upper motor neurons?

A

False, some of the descending fibers that originate here are not upper motor neurons; instead they terminate on sensory neurons in the brainstem and spinal cord

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22
Q

What are corticospinal and corticobulbar and how do they exit the cerebral hemisphere?

A

Projection fibers that leave the cerebral hemisphere through the posterior limb of the internal capsule

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23
Q

How is the internal capsule organized?

A 
Anterior to posterior:
Pyramidal system
Somatosensory system
Visual data
Auditory data
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24
Q

Where do fibers from the posterior limb of the internal capsule continue to?

A

Fibers continue into the cerebral crus of the midbrain

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25
Q

What is the somatotopical organization in the cerebral crus of the midbrain?

A

Pyramidal fibers are in middle 1/3 of cerebral crus

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26
Q

Where in the pons do corticospinal and corticobulbar descend through?

A

Through the basilar pons in (fascicle-like) bundles

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27
Q

What do the corticospinal and corticobulbar form as they enter the medulla?

A

Form the pyramis and maintain the somatopical organization

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28
Q

As pyramidal fibers descend through the brainstem, where do corticobulbar fibers terminate?

A

Terminate on motor nuclei of cranial nerves on lower motor neurons

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29
Q

What happens to a majority (85%) of the corticospinal fibers that descend through the pyramids?

A

85% of the fibers decussate in the pyramidal decussations

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30
Q

Where do the decussated corticospinal fibers descend through in the spinal cord and what do they form?

A

Descend through the lateral funiculus and form the lateral corticospinal tract

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31
Q

How are the fibers in the lateral corticospinal tract somatopically organized?

A 
Medial = fibers that terminate in cervical cord
intermediate =  fibers that terminate in upper extremity
Lateral =  fibers that terminate in lumbosacral
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32
Q

Where do most fibers of the lateral corticospinal tract terminate?

A

In the cervical cord segments

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33
Q

Where and how do most corticospinal fibers ultimately influence lower motor neurons in?

A

The ventral horn

1) some directly on LMNs
2) many end on interneurons that then influence LMNs

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34
Q

What percentage of corticospinal fibers in the pyramids do not decussate?

A

15%

35
Q

Where do the uncrossed corticospinal fibers that descend and what do they form?

A

Descend into the anterior funiculus form the anterior corticospinal tract

36
Q

Where do most of the anterior corticospinal tract fibers ultimately decussate?

A

At the segmental level although some do terminate on the ipsilateral side

37
Q

Where do most of the anterior corticospinal tract fibers terminate?

A

Most terminate in the cervical cord

38
Q

How do most fibers of the of the anterior corticospinal tract influence LMN activity?

A

Both directly and indirectly influence lower motor neurons

39
Q

Where do some corticospinal fibers that originate in the pariental lobe terminate, instead of onto sensory neurons?

A

On dorsal horn neurons and modify the transmission of sensory data through ascending pathways

40
Q

What do corticospinal and corticobulbar tracts help to provide for?

A

voluntary control of motor activities that involve the distal parts of the extremities and face

41
Q

What skilled movements do corticospinal and corticobulbar tracts help control?

A 
Face muscles:
1) eye
2) tongue
3) facial expression
Distal Extremities:
1) Fingers
2) Toes
42
Q

What factors do corticospinal and corticobulbar tracts allow the skilled movement areas to be performed with?

A

Speed
Agility
Precision

43
Q

What does a pure lesion of the corticospinal tracts do?

A

Hypotonia of contralateral muscles - especially of distal extremities and face

Decreases muscle tone -> flaccid (limpness)

44
Q

What happens initially with a pure lesion of the corticospinal tracts

A

Initial period of flaccid paralysis contralateral to lesion - especially of distal extremities and face

45
Q

What happens after several months with a pure lesion of the corticospinal tracts?

A

Motor control returns and any chronic loss of voluntary motor control is minimal (therefore no permanent paralysis)

46
Q

What persists after several months with a pure lesion of the corticospinal tracts?

A

Permanent difficulty performing highly skilled activities with the distal extremities (ie: picking up and manipulating small objects) and execution of movements that require much attention. Loss of speed, agility and precision of movements

47
Q

Where do corticobulbar projections originate from?

A

Upper motor neurons that are located in the inferior 1/3 of the precentral gyrus, the premotor area and areas of the parietal lobe

48
Q

Where do corticobulbar projections descend through to reach the brainstem?

A

Descend through the posterior limb of the internal capsule and into the brainstem where most terinate on interneurons that influence LMNs of cranial nerves.

49
Q

What motor nuclei of the cranial nerves receive corticobulbar innervation?

A 
Oculomotor nuclear complex
trochlear nucleus
trigeminal motor nucleus
abducens nucleus
facial motor nucles
nucleus ambiguus
hypoglossal nucleus
50
Q

What does the oculomotor nuclear complex innervate?

A

includes LMNs, innervates skeletal muscle of III nerve

51
Q

What does the trochlear nucleus innervate?

A

includes LMNs, innervates skeletal muscle of IV nerve

52
Q

What does the trigeminal motor nucleus innervate?

A

includes LMNs, innervates skeletal muscle of V nerve

53
Q

What does the abducens nucleus innervate?

A

includes LMNs, innervates skeletal muscle of VI nerve

54
Q

What does the facial motor nucleus innervate?

A

includes LMNs, innervates skeletal muscle of VII nerve

55
Q

What does the nucleus ambiguus innervate?

A

includes LMNs of IX, X and cranial root of XI nerve

56
Q

What does the hypoglossal nucleus innervate?

A

includes LMNs, innervates skeletal muscle of IV nerve

57
Q

Which nuclei do not receive direct corticobulbar innervation?

A

CN III, IV, VI

58
Q

What cranial nerves follow direct corticobulbar innervation?

A

CN V, VII, IX, X, cranial root XI and XII

59
Q

Which motor nuclei are innervated by corticobulbar fibers on the contralateral side?

A

V, VII nucleus ambiguus and XII

60
Q

What is significant about corticobulbar fibers that end ipsilaterally?

A

Most LMNs of cranial nerves receive bilateral corticobulbar innervation and there is no significant paralysis of most muscles (since innervated by cranial nerves following unilateral lesions of corticobulbar fibers)

61
Q

What are some exceptions to the pattern of bilateral corticobulbar fiber innervations?

A

The neurons of facial motor nucleus that innervate:
1) facial expression of lower 1/2 of face
2) neurons of the hypoglossal nucleus (sometimes)
These only receive from controlateral corticobulbar innervation

62
Q

Why is an understanding of the pattern of corticobulbar innervation to LMN’s of cranial nerves important clinically?

A

Unilateral corticobulbar (upper motor neuron) lesions will only affect muscles of facial expression only lower 1/2 of face and muscles of tongue (all other muscles innervated by cranial nerves are unaffected)

63
Q

Why are the innervation of motor nuclei II, IV and VI different than other motor nuclei?

A

The activity of the LMNs of these nerves are coordinated to ensure that both eyes maintain visual fixation on the same object in the visual field

64
Q

What are vergence movements?

A

When eyes move in opposite directions

65
Q

What are the two types of vergence movements?

A

Divergence

Convergence

66
Q

What is divergence

A

both eyes abduct (focus on distant object)

67
Q

What is convergence?

A

both eyes adduct

68
Q

What are conjugate movements?

A

when eyes move in parallel

69
Q

What are involuntary conjugate movements?

A

include visual tracking maneuvers when watching an object move across the visual field (ie: smooth pursuit movement = automatic tracking movements)

70
Q

What is the area of the cortex that controls the automatic tracking of movements?

A

Occipital lobe, also vestibular driven movements

71
Q

What are the voluntary conjugate movements that occur when scanning a landscape or a page known as and how do they appear?

A

Known as saccadic eye movements

- series of brisk, jerky, fast , excursional movements

72
Q

What area of the cerebral cortex controls saccadic eye movements?

A

The area of the cerebral cortex that controls this activity is located in the posterior part of the middle frontal gyrus and is called the frontal eye field

73
Q

What brodmann’s map area is the frontal eye field?

A

8

74
Q

What does unilateral stimulation of the frontal eye field result in?

A

conjugate, saccadic movements of eyes to the opposite side

75
Q

Do the visual cortex or FEF neurons directly project axons to the motor nuvlei of III, IV or VI

A

no

76
Q

Where do the visual cortex or FEF neurons project axons to?

A

Superior colliculus in the midbrain

77
Q

Where do visual cortex or FEF neurons that have reached the superior colliculus project to?

A

Send fibers to other neurons of the brainstem that coordinate conjugate movements of the eyes

78
Q

What does conjugate movement of the eyes in the horizontal plane require and what does it form?

A

The participation of special neurons in the brainstem which form the paramedian pontine reticular formation

79
Q

Where is the paramedian pontine reticular formation found?

A

located in the lower pons (near VI nucleus)

80
Q

Where does the paramedian pontine reticular formation receive input from?

A

Superior colliculus
Vestibular info
Vestibular nuclear complex

81
Q

Where do paramedian pontine reticular formation send axons through and to?

A

Through the ascending medial longitudinal fasciculus to the Nuclei of III, IV, VI

82
Q

What do the neurons of the paramedian pontine reticular formation do when activated?

A

Neurons of the paramedian pontine reticular formation ensures that LMNs of III, IV, and VI are activated such that the eyes move ina conjugate fashion in the horizontal plane

83
Q

What occurs with lesions in the frontal eye field?

A
  • Paralysis of voluntary gaze to side opposite of lesion

- preservation of smooth pursuit movements

84
Q

What occurs with lesions in the paramedian pontine reticular formation?

A

1) paralysis/loss of lateral gaze towards the lesioned side

2) includes loss of voluntary gaze and smooth pursuit

Neuroanatomy Exam II (11 decks)

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