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Human Physiology 2 - Unit 2 - Zach H. > Lecture 11: Spinal Cord, Brainstem, & Cortex Control of Motor Function II > Flashcards

Lecture 11: Spinal Cord, Brainstem, & Cortex Control of Motor Function II Flashcards

1
Q

What is the definition of the pyramidal system?

A

These are tracts that pass through the medullary pyramidals. (other motor pathways are extrapyramidal)

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2
Q

Which two tracts make up the pyramidal system?

A

> corticospinal tract

> corticobulbar tract

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3
Q

Where do upper motor neurons originate?

A

motor cortices

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4
Q

What percentage of upper motor neurons decussate in pyramids and form the lateral corticospinal tracts?

A

75-85%

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5
Q

Where do most upper motor neurons synapse?

A

With association neurons in spinal cord central gray matter.

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6
Q

You know that 75-85% of upper motor neurons decussate in pyramids and form the lateral corticospinal tracts. Where do the remaining upper motor neurons decussate?

A

Remainder decussate near synapse with lower motor neurons and form anterior corticospinal tracts.

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7
Q

How are upper motor neurons classified?

A

Classified according to where they synapse in the ventral horn:

  • medial activation system
  • lateral activation system
  • nonspecific activating system
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8
Q

What muscles are innervated by the medial activation system?

A

postural and girdle muscles

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9
Q

What muscle control is the lateral activation system associated with?

A

Associated with distally located muscles used for fine movements.

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10
Q

What system of upper motor neurons facilitates local reflex arcs?

A

nonspecific activating system

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11
Q

What makes up the lateral corticospinal tract?

A

Corticospinal fibers that have crossed in medulla.

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12
Q

What makes up the anterior corticospinal tract?

A

Uncrossed corticospinal fibers that cross near level of synapse with LMSs.

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13
Q

What does the lateral corticospinal tract supply?

A

ALL levels of spinal cord.

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14
Q

What does the anterior corticospinal tract supply?

A

Neck and upper limbs.

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15
Q

What are the 3 origins of the corticospinal tract (pyramidal tract)?

A

> primary motor cortex
pre-motor cortex
somatosensory area

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16
Q

True or False:

In the corticospinal tract, some fibers do not cross but continue down ipsilaterally in ventral corticospinal tract.

A

True

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17
Q

What is the pathway of the corticospinal tract?

A

site of origin -> internal capsule -> medullary pyramids -> X in lower medulla (most fibers) -> lateral columns of spinal cord (lateral corticospinal tract).

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18
Q

Where are giant pyramidal (Betz) cells located?

A

in motor cortex

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19
Q

What do giant pyramidal (Betz) cells do?

A

send collaterals back to cortex

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20
Q

What percentage of the fibers in the corticospinal tract are giant pyramidal (Betz) cells?

A

3%

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21
Q

What are the functions of the corticospinal tract?

A

> Adds speed and agility to conscious movements.
- especially movements of the hand
Provides a high degree of motor control.
- (i.e., movement of individual fingers)

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22
Q

What are some symptoms of a patient with a corticospinal tract lesion?

A 
> reduced muscle tone
> clumsiness 
> weakness 
> not complete paralysis 
> NOTE: complete paralysis results if both pyramidal and extrapyramidal systems are involved (as is often the case).
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23
Q

In the corticospinal tract, where do other fibers from the cortex, besides giant pyramidal (Betz) cells, go?

A

> pass into caudate nucleus and putamen
pass to red nucleus
pass to reticular substance and vestibular nuclei
large numbers of fibers pass to pontine nuclei

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24
Q

What does the corticobulbar tract innervate?

A

the head

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25
Q

Where do most fibers of the corticobulbar tract terminate?

A

In reticular formation near cranial nerve nuclei.

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26
Q

What do association neurons of the corticobulbar tract synapse with?

A

lower motor neurons

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27
Q

True or False:
Association neurons in the corticobulbar tract leave the reticular formation and synapse in cranial nerve nuclei and also lower motor neurons.

A

True

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28
Q

large neurons from the magnocellular region of the red nucleus give rise to what tract?

A

rubrospinal tract

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29
Q

Where does the rubrospinal tract decussate?

A

decussates in lower brain stem

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30
Q

What synapses in the magnocellular portion of the red nucleus?

A
  • fibers from primary motor cortex (corticorubral pathway)

- branches from corticospinal tract

31
Q

True or False:

The magnocellular region of the red nucleus has a somatotopic representation of all the muscles of the body.

A

True

32
Q

What does stimulation of the red nucleus result in?

A

> stimulation of flexors

> inhibition of extensors (antigravity muscles)

33
Q

What does the extrapyramidal system include?

A

> pathways that contribute to motor control but that are not part of the corticospinal system

> descending motor tracts that do not pass through medullary pyramids or corticobulbar tracts

> rubrospinal tracts
vestibulospinal tracts
reticulospinal tracts

34
Q

What are the characteristics of the rubrospinal tract?

A

> originates in red nucleus
decussates in midbrain
descends in lateral funiculus (column)
function is closely related to cerebellar function

35
Q

What do patients with a lesion in the rubrospinal tract present with?

A

> impairment of distal arm and hand movement

> intention tremors (similar to cerebellar lesions)

36
Q

Where does the rubrospinal tract originate?

A

red nucleus

37
Q

Where do fibers in the rubrospinal tract decussate?

A

midbrain

38
Q

In which column does the rubrospinal tract descend?

A

lateral funiculus

39
Q

Is the function of the rubrospinal tract closely related to cerebellar function?

A

Yes

40
Q

Where does the vestibulospinal tract originate at?

A

in vestibular nuclei

41
Q

Where does the vestibular nuclei receive major input from?

A

vestibular nerve (CN VIII)

42
Q

In which column does the vestibulospinal tract descend?

A

anterior funiculus

43
Q

What does the vestibulospinal tract fibers descending in the anterior funiculus synapse with?

A

LMNs to extensor muscles

44
Q

You know that the vestibulospinal tract fibers synapse with LMNs to extensor muscles. What are they primarily involved in?

A

Maintenance of upright posture.

45
Q

Where does the reticulospinal tract originate at?

A

various regions of reticular formation

46
Q

Which column does the fibers of the reticulospinal tract descend?

A

anterior portion of lateral funiculus

47
Q

What is the function of the reticulospinal tract?

A

thought to mediate larger movements of trunk and limbs that DO NOT require balance or fine movements of upper limbs

48
Q

What does the pontine reticular nuclei do?

A

Stimulatory effect on both extensors and flexors, but especially extensors (antigravity muscles).

49
Q

What do the fibers of the pontine reticular nuclei make up?

A

pontine reticulospinal tract (anterior column)

50
Q

What do the fibers of the medullary reticular nuclei make up?

A

medullary reticulospinal tract (lateral column)

51
Q

What does the medullary reticular nuclei do?

A

Inhibitory effect on both extensors and flexors, especially extensors (antigravity muscles)

52
Q

Does the pontine reticular nuclei or medullary reticular nuclei have inhibitory effects on extensors and flexors?

A

medullary reticular nuclei

pontine reticular nuclei have stimulatory effect

53
Q

Do the fibers from the pontine reticular nuclei or medullary reticular nuclei run in the anterior column?

A

pontine reticular nuclei fibers

medullary reticular nuclei fibers run in lateral column

54
Q

What are the components of the vestibular apparatus?

A

> Utricle
Saccule
Semicircular canals

55
Q

In the vestibular apparatus, what kind of lymph are the ducts filled with and what kind of lymph surrounds the ducts?

A

Ducts are filled with endolymph and surrounded by perilymph.

56
Q

What does the vestibular apparatus detect?

A

Detects angular (semicircular canals) and linear (utricle and saccule) acceleration of the head.

57
Q

What is the vestibular apparatus involved in?

A

Reflex adjustments of head, eyes, and postural muscles.

58
Q

What does the vestibular apparatus provide for us?

A

A stable visual image and steady posture.

59
Q

True or False:

Each semicircular canal has an enlargement at one end called the ampulla, which contains hair cells.

A

True

60
Q

True or False:

The utricle and saccule each contain a macula, which contains hair cells.

A

True

61
Q

What is the vestibular apparatus?

A

A membranous labyrinth consisting of three semicurcular canals and vestiuble (also includes cochlea).

62
Q

Is the macula of the utricle or saccule located on a horizontal plane?

A

Macula of Utricle

63
Q

What does the macula of the utricle do?

A

Plays role in determining orientation of head when head is upright.

64
Q

What does the macula of the saccule do?

A

Signals head orientation when person is lying down.

65
Q

In which plane is the macula of the saccule located?

A

vertical plane

66
Q

What are the characteristics of the macula?

A

Each macula is covered by a gelatinous layer:
> contains large number of embedded small calcium carbonate crystals (statoconia)

> contains thousands of hair cells which project cilia into the gelatinous layer

> the weight of the statoconia bends cilia in the direction of gravitational pull

67
Q

What are the characteristics of a hair cell?

A

> has 50-70 small cilia (stereocilia)
has 1 large cilium (kinocilium) off set to one side
tips of stereocilia are connected together and to kinocilium

68
Q

What are fuctions of the hair cell in the macula?

A

> bending of sterocilia towards kinocilium opens hundreds of cation channels causing receptor membrane depolarization and excitation

> bending of cilia in opposite direction closes channels and hyperpolarizes receptor membrane

> hair cells are oriented such that bending the head in different directions causes different groups of hair cells to depolarize

69
Q

What happens in the semicircular canals when the head begins to rotate in any direction?

A

> inertia of the fluid in one or more of the semicircular canals remains stationary while semicircular canal rotates with the head

> fluid flows from the duct and through the ampulla and causes the cupula to bend to one side

> hundreds of hair cells within each cupula detect this bending and send signals via the vestibular nerve

70
Q

How is the semicircular canal aligned when the head is bent forward 30 degrees?

A

> lateral ducts are horizontal
anterior ducts are in vertical planes projecting forward and 45 degrees outward
posterior ducts are in vertical planes projecting backward and 45 degrees outward

71
Q

What are the characteristics of the ampulla found at one end of each semicircular canal duct?

A

> filled (along with duct) with endolymph
crista ampullaris
- small crest within each ampulla
cupula
- loose mass of gelatinous tissue on top of the crista

72
Q

What is the ampulla filled with?

A

Filled (along with duct) with endolymph (high[K]; low [Na])

73
Q

What is the crita ampullaris?

A

small crest within each ampulla

74
Q

What is the cupula?

A

loose mass of gelatinous tissue on top of the crista

Human Physiology 2 - Unit 2 - Zach H. (11 decks)

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