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Neuroanatomy > 1/23 Motor Pathways > Flashcards

1/23 Motor Pathways Flashcards

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1
Q

What do upper motor neurons do?

A

carry motor outputs from cerebral cortex/brainstem to lower motor neurons in brainstem/ spinal cord

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2
Q

Where are lower motor neurons, what do they do?

A

cell bodies in brainstem or spinal cord; innervate muscles in the periphery

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3
Q

What are the types of lower motor neurons?

A

alpha, gamma, beta

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4
Q

What are alpha motor neurons, what do they innervate?

A

large cell bodies; axons innervate skeletal muscle

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5
Q

What are gamma motor neurons, what do they innervate?

A

smaller axon fiber diameter; innervate muscle spindles to help control stretch reflexes

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6
Q

What are beta motor neurons, what do they innervate?

A

least abundant; innervate muscle fibers both in and out of muscle spindles

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7
Q

What are the symptoms of a lower motor neuron lesion?

A

Muscle weakness and atrophy
Fasciculations
Decreased tone
Hyporeflexia

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8
Q

What are the symptoms of a upper motor neuron lesion?

A

Muscle weakness
Increased tone
Hyperreflexia
Abnormal reflexes/signs

*acute UMN lesions may initially present with flaccid paralysis, decreased tone, and hyporeflexia

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9
Q

What are the origins of the major pathways?

A

cortical, brainstem
lateral, medial

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10
Q

What do lateral pathways control?

A

appendicular muscles (limbs)

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11
Q

What do medial pathways control?

A

axial/girdle postural muscles

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12
Q

How do medial pathways descend? What kind of influence do they have?

A

descend ipsilaterally
bilateral influence because they synapse in on interneurons in the intermediate zone as well as LMNs in the ventral horn

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13
Q

What are the major pathways with cortical origin? Are they lateral or medial?

A

Lateral corticospinal (lateral)
Ventral corticospinal (medial)
Corticobulbar (lateral)

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14
Q

What are the major pathways with brainstem origin? Are they lateral or medial?

A

rubrospinal (lateral)
vestibulospinal (medial)
tectospinal (medial)
reticulospinal (medial)

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15
Q

What does the lateral corticospinal tract control?

A

Rapid, dexterous movements at individual joints, particularly the limbs.

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16
Q

Where does the lateral corticospinal tract originate?

A

Most fibers originate in primary motor cortex, precentral gyrus. Other neurons originate in premotor, supplementary motor, or parietal lobe. Cortical layer 5.

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17
Q

Where/how do the axons descend in the lateral corticospinal tract?

A

Axons descend as part of the corona radiata, through the posterior limb of the internal capsule.
Continue into the cerebral peduncles of midbrain – middle 1⁄3 of crus cerebri, then through the ventral pons.
Ventral surface of the medulla as the pyramids.
Axons cross in the caudal medulla as the pyramidal decussation.
Descend in the lateral funiculus of the spinal cord and synapse on cell bodies of LMNs in the ventral horn

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18
Q

What does the corticobulbar tract control?

A

Movement of the facial, tongue, jaw, laryngeal, and pharyngeal muscles. NOT extraocular muscles.

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19
Q

Where does the corticobulbar tract originate?

A

Cell bodies in the lateral aspect of precentral gyrus project descending axons through the genu of the internal capsule.

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20
Q

Where/how do the axons descend in the corticobulbar tract?

A

descending axons through the genu of the internal capsule.
Projections through the brainstem to the facial motor nucleus, trigeminal motor nucleus, nucleus ambiguus, and hypoglossal nucleus.
• Projections to facial motor nucleus (pons): bilateral to the portion of the nucleus controlling upper face, contralateral to the lower face.

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21
Q

What are the symptoms of lesions of the corticobulbar tract?

A

weakness of contralateral lower face
upper face spared because bilaterally innervated

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22
Q

What are the symptoms of lesions of the facial motor nucleus?

A

ipsilateral whole face paralysis

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23
Q

What are the symptoms of lesions of the facial nerve?

A

ipsilateral whole face paralysis

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24
Q

Where does the corticobulbar tract have projections to?

A

trigeminal motor nucleus
nucleus ambiguus
hypoglossal nucleus
spinal accessory nucleus

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25
Where is the trigeminal motor nucleus? What laterality are the projections?
mid-pons bilateral projections
26
Where is the nucleus ambiguus? What laterality are the projections?
rostral medulla bilateral projections innervates laryngeal and pharyngeal muscles
27
Where is the hypoglossal nucleus? What laterality are the projections?
rostral dorsal medulla most often bilateral projections
28
Where is the spinal accessory nucleus? What laterality are the projections?
caudal medulla bilateral projections but not symmetrical
29
What does the rubrospinal tract control?
Influences movements of the upper limbs; exact function unclear in humans.
30
Where does the rubrospinal tract originate?
neurons whose cell bodies are in the red nucleus
31
Where/how do the axons descend in the rubrospinal tract?
Axons decussate immediately in the midbrain and descends in the dorsolateral aspect of pons and medulla. Descends in the lateral funiculus of the spinal cord then synapse in the ventral horn of the cervical cord.
32
In comatose patients, what happens in response to painful stimulus with corticospinal tract damage above the red nucleus?
Upper limb flexor posturing
33
In comatose patients, what happens in response to painful stimulus with brainstem damage below the red nucleus?
upper limb extensor posturing
34
What is the lower limb flexion reflex, what does it depend on?
triple flexion (hip, knee, ankle); Dependent only on spinal cord reflex circuits.
35
What does the ventral corticospinal tract control?
bilateral axial and girdle (shoulder) muscles.
36
Where does the ventral corticospinal tract originate?
Axons originate with the lateral cortical spinal tract and travels with it until the pyramidal decussation.
37
Where/how do the axons descend in the ventral corticospinal tract?
Tract remains uncrossed and descends into the ventral funiculus of the cord. Some axons cross in the spinal cord before synapsing on LMNs and interneurons in the ventral horn and intermediate zone, respectively. *Tract projects only to cervical and upper thoracic spinal cord
38
What does the vestibulospinal tracts control?
Critical for maintaining balance and posture. Receive input from vestibular organs (semicircular canals, utricle, saccule)
39
Where do the vestibulospinal tracts originate?
Cell bodies in the medial and lateral vestibular nuclei of medulla and pons.
40
How do the axons descend in the vestibulospinal tract?
as the vestibulospinal tracts lateral and medial tracts
41
Where/how do the axons descend in the lateral vestibulospinal tract?
descends ipsilaterally in the ventral funiculus of the spinal cord. Synapse in ventral horn on LMNs and interneurons at all spinal levels.
42
What does the lateral vestibulospinal tract control?
Posture and balance – neck, back, hip and leg muscles.
43
Where/how do the axons descend in the medial vestibulospinal tract?
descends bilaterally to the superior levels of the cervical spinal cord
44
What does the medial vestibulospinal tract control?
Role in controlling head position related to eye position.
45
Where does the tectospinal tract originate?
neurons in deep layers of the superior colliculus (tectum).
46
Where/how do the axons descend in the tectospinal tract?
Projects inferiorly to the cervical spinal segments.
47
What does the tectospinal tract control?
Partial control of neck, shoulder, and upper trunk muscles. Superior colliculus is key for controlling eye movements, tectospinal tract has roles in eye/head movement coordination.
48
Where does the reticulospinal tract originate?
pontine/medullary reticular formation
49
Where/how do the axons descend in the reticulospinal tract?
Descend in the ventral funiculus; ipsilateral tract but exerts bilateral motor control.
50
What does the reticulospinal tract control?
Influences automatic movements, such as postural control/walking on uneven terrain
51
What are the types of spinal cord interneurons?
segmental, commissural, propriospinal
52
What are segmental interneurons?
Short axon that distributes branches ipsilaterally within a single spinal segment to synapse on motor neurons and other interneurons Receive convergent input from somatic sensory receptors for reflex control of movement
53
What are commissural interneurons?
Axons distribute bilaterally for movement coordination on both sides of the body; actions such as walking and postural stability
54
What are propriospinal interneurons?
Axons project for multiple spinal segments before synapsing on motor neurons Important for upper-lower limb coordination
55
A
gracile fascicle
56
B
cuneate fascicle
57
C
dorsal spinocerebellar tract
58
D
ventral spinocerebellar tract
59
E
anterolateral system
60
F
Lateral corticospinal tract
61
G
rubrospinal tract
62
H
medial vestibulospinal tract
63
I (i)
tectospinal tract
64
J
medullary reticulospinal tract
65
K
pontine reticulospinal tract
66
L
lateral vestibulospinal tract
67
M
ventral corticospinal tract
68
What are the frontal lobe motor areas?
supplementary motor, premotor cortex, cingulate motor area
69
Where is the supplementary motor area and what is its role?
medial surface of cerebral hemisphere. Specific role unknown, possibly involved in planning bimanual movements.
70
Where is the premotor cortex and what is its role?
lateral hemisphere, ventral to primary motor cortex. Two functional subdivisions for processing visual information: 1. Dorsal premotor: helps control reaching 2. Ventral premotor: helps control grasping • Contains mirror neurons that activate when watching others perform a movement; learning by imitation and meaning of movements
71
Where is the cingulate motor area and what is its role?
medial surface, deep in the cingulate sulcus; part of the limbic system (emotional regulation)
72
What happens with damage to the premotor areas?
apraxia, motor planning disorders Loss of ability to produce learned purposeful movements, even though person is physically capable of producing the movements.
73
What is the cortical integration for visually guided movement in the decision to move?
limbic and prefrontal association cortices, involved in motivation, emotions, and cognition projecting to premotor and primary motor cortices
74
What is the cortical integration for visually guided movement in the visual system?
projects information via the ‘where’ pathway to the posterior parietal cortex, which is important for identifying locations of objects of interest and directing attention to them. This information sent to premotor areas of frontal lobe to form the plan of action for movement.
75
What is the cortical integration for visually guided movement in the visual system and the decision to move culminate in?
activation of descending motor pathways
76
What is multiple sclerosis?
Autoimmune inflammatory disorder of CNS myelin
77
What appears on MRI with multiple sclerosis?
Plaques of demyelination can appear and disappear in multiple locations of the CNS over time
78
What is the incidence ration in multiple sclerosis?
3:1 female:male
79
What is guillain-barré syndrome?
Immune-mediated demyelination of peripheral nerves (some forms affect axons or nodes of Ranvier)
80
What is the onset of guillain-barre syndrome?
Onset typically 1 to 2 weeks following viral illness or bacterial infection
81
What is the presentation of guillain-barré syndrome?
ascending progressive weakness, areflexia, tingling paresthesia of hands and feet. Motor involvement typically more severe than sensory. Symptoms are the worst 1 to 3 weeks after onset, recovery takes many months
82
What are motor neuron diseases?
Degenerative disorders of upper and/or lower motor neurons. Produce motor deficits without sensory disturbances or findings.
83
What is an example of a motor neuron disease?
Amyotrophic Lateral Sclerosis (ALS)
84
What is Amyotrophic Lateral Sclerosis (ALS)?
Gradual degeneration of upper and lower motor neurons Eventually leads to respiratory failure and death Early signs: focal weakness/clumsiness that spreads to adjacent muscle groups

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