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Phys II > Lecture 10 > Flashcards

Lecture 10 Flashcards

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1
Q

What is a pyramidal system?

A

Tracts that pass through the medullary pyramids

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2
Q

What are the components of the pyramidal system?

A

Corticospinal tract, corticobulbar tract

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3
Q

Where do the UMN of the pyramidal system originate?

A

Motor cortices

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4
Q

What percentage of UMN decussate in the pyramids and form the lateral corticospinal tracts?

A

75-85%

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5
Q

What do most of the UMN of the pyramidal system synapse with?

A

Association neurons in spinal cord central grey

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6
Q

How are UMN of the pyramidal system classified?

A

According to where they synapse in the ventral horn (medial or lateral)

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7
Q

What do UMN that synapse in the medial activation system innervate?

A

Postural and girdle muscles

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8
Q

What are UMN that synapse in the lateral activation system associated with?

A

Distally located muscles used for fine movements

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9
Q

The corticospinal tract is also referred to as the ___ tract.

A

Pyramidal

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10
Q

List the origins of the corticospinal tract.

A

Primary motor cortex, premotor cortex, somatosensory area

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11
Q

Outline 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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12
Q

What is the lateral corticospinal tract division of the corticospinal tract made up of?

A

Corticospinal fibers that have crossed in the medulla

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13
Q

What is the anterior corticospinal tract division of the corticospinal tract made up of?

A

Uncrossed corticospinal fibers that cross near the level of synapse with LMNs

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14
Q

What does the lateral corticospinal tract supply?

A

All levels of the spinal cord

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15
Q

What does the anterior corticospinal tract supply?

A

Neck and upper limbs

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16
Q

What are the functions of the corticospinal tract?

A

Adds speed and agility to conscious movements, provides a high degree of motor control

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17
Q

Where are giant pyramidal (Betz) cells located?

A

Motor cortex

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18
Q

How much of the corticospinal tract do Betz cells make up?

A

3%

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19
Q

What do Betz cells synapse on?

A

Directly on LMNs, especially those that innervate forearm and hand muscles

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20
Q

T or F: Betz cells are large (60 um) with large fibers (16 um) that transmit at 70 m/sec.

A

True.

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21
Q

What do Betz cells sens back to the cortex?

A

Collaterals

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22
Q

What do corticospinal tract lesions lead to?

A

Reduced muscle tone, clumsiness, weakness, not complete paralysis

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23
Q

When does complete paralysis often result?

A

Both pyramidal and extrapyramidal systems are involved

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24
Q

In the corticobulbar tract, where do association neurons leave and synapse?

A

Leave reticular formation and synapse in cranial nerve nuclei or synapse with LMN

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25
In the corticobulbar tract, where do most fibers terminate?
Reticular formation near cranial nerve nuclei
26
T or F: Corticobulbar tract lesions are typically bilateral.
Corticobulbar tract lesions are typically unilateral.
27
What do corticobulbar tract lesions typically result in?
Mild muscle weakness
28
What does a lesion of CN XII result in?
Paralysis of the ipsilateral side (deviation of tongue toward damaged side)
29
What does a lesion of CN VII result in?
Spastic paralysis of the ipsilateral lower 1/4 of face
30
What pathways does the extrapyramidal system include?
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
31
What tracts does the extrapyramidal system include?
Rubrospinal, vestibulospinal, reticulospinal, olivospinal
32
What do the extrapyramidal subcortical nuclei include?
Substantia nigra, caudate, putamen, globus pallidus, thalamus, red nucleus, subthalamic nucleus
33
What is the relationship between the red nucleus and the magnocellular region, rubrospinal tract, and skeletal muscles?
Fibers from primary motor cortex and branches from corticospinal tract synapse in magnocellular portion of red nucleus; Large neurons from magnocellular region of red nucleus give rise to rubrospinal tract which decussates in lower brain stem; Magnocellular region has a somatotopic representation of all the muscles of the body
34
What does stimulation of the red nucleus result in?
Stimulation of flexors, inhibition of extensors
35
T or F: The red nucleus is an evolutionarily primitive portion of the brain.
True.
36
What is the relay center of the red nucleus?
Relays information from motor cortex to cerebellum
37
What does the red nucleus have projections to?
Contralateral spinal cord via rubrospinal tract or ipsilateral inferior olive
38
Where does the rubrospinal tract originate?
Red nucleus
39
Where does the rubrospinal tract decussate?
Midbrain
40
Where does the rubrospinal tract descend?
Lateral funiculus
41
Function of the rubrospinal tract is closely related to what function?
Cerebellum
42
What is the rubrospinal tract responsible for?
Large muscle movement and some fine motor of UE
43
Lesions of the rubrospinal tract can lead to what?
Impairment of distal arm and hand movement, intention tremors, may take over for injured corticospinal tract in some animals
44
Where does the vestibulospinal tract originate?
Vestibular nuclei
45
What does the vestibulospinal tract receive and what is the goal?
Receives major input from vestibular nerve (CN VIII) about changes in head position; Goal of maintaining balance
46
Where does the vestibulospinal tract descend?
In anterior funiculus
47
What does the vestibulospinal tract synapse with?
LMNs to extensor muscles (involved in maintenance of upright posture)
48
Describe the lateral vestibulospinal tract.
Major part of tract, ipsilateral, to lumbar region of SC, upright posture and balance, extensors of LE and trunk
49
Describe the medial vestibulospinal tract.
Projects bilaterally, controls LMN of CN XI and projects indirectly to CN VI and III
50
Where does the reticulospinal tract originate?
In various regions of the reticular formation
51
Where does the reticulospinal tract descend?
IN anterior portion of lateral funiculus
52
What is the reticulospinal tract thought to mediate?
Larger movements of trunk and limbs that do not require balance or fine movements of upper limbs
53
T or F: The reticulospinal tract controls the activity of only alpha motor neurons.
False. The reticulospinal tract controls the activity of alpha and gamma motor neurons.
54
Fibers of the pontine reticular nuclei make up which tract?
Pontine reticulospinal tract (anterior column)
55
Fibers of the medullary reticular nuclei make up which tract?
Medullary reticulospinal tract (lateral column)
56
What type of effect do the pontine reticular nuclei have on extensors and flexors?
Stimulatory (especially on extensors)
57
What type of effect do the medullary reticular nuclei have on extensors and flexors?
Inhibitory (especially on extensors)
58
What is the vestibular apparatus?
Membranous labyrinth consisting of 3 semicircular canals and vestibule
59
What is the vestibule composed of?
Utricle, saccule, semicircular canals
60
What are the ducts of the vestibular apparatus filled with and surrounded by?
Filled with endolymph and surrounded by perilymph
61
What does the vestibular apparatus do?
Detects angular and linear acceleration of head
62
T or F: The semicircular canals detect linear acceleration of the head.
False. The semicircular canals detect angular acceleration of the head. The utricle and saccular detect linear acceleration of the head.
63
What contains the hair cells in each utricle and saccule?
Macula
64
What contains the hair cells in each semicircular canal?
Ampulla
65
Describe the macula of the utricle.
Located on a horizontal plane, plays a role in determining orientation of the head when the head is upright
66
Describe the macule of the saccule.
Located in a vertical plane, signals head orientation when a person is lying down
67
What is each macula covered by? What does it contain?
Covered by a gelatinous layer; Contains a large number of embedded small calcium carbonate crystals (statoconia) and thousands of hair cells which project cilia into the gelatinous layer
68
What are the tips of the stereocilia connected to?
Together and to kinocilium
69
Trace the rubrospinal tract.
Originates in red nucleus → decussates in midbrain → descends in lateral funiculus
70
Explain how hair cells in the macula become depolarized and hyperpolarized.
Bending of stereocilia toward 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
71
Explain how semicircular canals are able to detect motion in the head in 3D space.
When the head begins to rotate in any direction, inertia of the fluid in one or more of the semicircular canals remains stationary while the 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.
72
What is the crista ampullaris?
Small crest within each ampulla
73
What is the cupula?
Loose mass of gelatinous tissue on top of crista
74
What is the ampulla? What is it filled with?
Enlargement at one end of each semicircular canal duct; Filled with endolymph
75
Trace the corticorubrospinal pathway.
Red nucleus receives a large number of direct fibers from the primary motor cortex through the corticorubral tract, as well as branching fibers from the corticospinal tract as it passes through the mesencephalon. These fibers synapse in the lower portion of the red nucleus, which then give rise to the rubrospinal tract, which crosses to the opposite side in the lower brain stem and follows a course immediately adjacent and anterior to the corticospinal tract into the lateral columns of the spinal cord.

Phys II (8 decks)

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