Module 4: Corticospinal Tract and Other Motor Pathways Flashcards
1
Q
What are the 3 most important motor and sensory “long tracts”?
A
Lateral corticospinal tract
Posterior columns
Anterolateral pathways
2
Q
What is the function of the lateral corticospinal tract?
A
Motor
3
Q
What is the function of the posterior columns?
A
Sensory (vibration, joint position, fine touch)
4
Q
What is the function of the anterolateral pathways?
A
Sensory (pain, temperature, crude touch)
5
Q
Where are the primary motor cortex and primary somatosensory cortex located in the brain?
A
On either side of the central/Rolandic sulcus, which divides the frontal lobe from the parietal.
6
Q
Which Brodmann’s area(s) are associated with the primary motor cortex?
A
Brodmann’s area 4
7
Q
The primary motor cortex is in the ________ gyrus, while the primary somatosensory cortex is in the ________ gyrus.
A
Precentral; postcentral
8
Q
Which Brodmann’s area(s) are associated with the primary somatosensory cortex?
A
Brodmann’s areas 3, 1, 2
9
Q
Lesions in the primary motor and primary somatosensory cortices cause deficits on which side of the body?
A
The contralateral side
10
Q
Where does the motor association cortex lie in relation to the primary motor cortex?
A
anterior
11
Q
Name the two areas of the brain that consist of the motor association cortex.
A
supplementary motor areas (SMA)
premotor cortex
12
Q
What are SMA and premotor cortex involved in?
A
Higher-order motor planning
13
Q
Where do the SMA and premotor cortex project to?
A
primary motor cortex
14
Q
Where does the somatosensory cortex receive input from?
A
secondary parietal association cortex, which is important in higher-order somatosensory processing
15
Q
Which Brodmann’s area(s) are associated with the secondary parietal association cortex?
A
Brodmann’s areas 5 & 7
16
Q
T or F: Lesions in the sensory or motor association cortex do not produce severe deficits in basic movement or sensation.
A
T; Instead, lesions in the association cortices cause deficits in higher-order sensory analysis or motor planning.
17
Q
How are the primary motor and somatosensory cortices organized?
A
somatotopically, meaning adjacent regions on the cortex correspond to adjacent areas on the body surface.
18
Q
How are cortical maps classically depicted?
A
by a motor homunculus and a sensory homunculus.
19
Q
List the somatotopic organization going from the lateral surface of the cortex to the medial surface.
A
Goes from throat to face to hand/arm to the leg.
20
Q
T or F: Somatotopic organization is confined to the cortex.
A
F: most motor and sensory pathways maintain a rough somatotopic organization along their entire length, which can be traced back from one level to the next in the nervous system.
21
Q
What are two synonyms for column?
A
tract or funiculus
22
Q
What is the butterfly-shaped center of the spinal cord called?
A
central gray matter
23
Q
What is the central gray matter surrounded by?
A
ascending and descending white matter columns/tracts/funiculi
24
Q
Where are the sensory neurons of the spinal tract located?
A
dorsal root ganglia
25
Sensory information is carried from the periphery into the dorsal aspect of the cord through ______.
dorsal nerve root filaments
26
Name the 3 segments of the central gray matter.
dorsal/posterior horn
intermediate zone
ventral/anterior horn
27
What is the dorsal horn of the central gray matter mainly involved in?
sensory processing
28
What does the intermediate zone of the central gray matter contain?
interneurons
29
What is the ventral horn of the central gray matter contain?
motor neurons
30
What are the 3 components of the spinal cord white matter?
Dorsal/posterior columns
Lateral columns
Ventral/anterior columns
31
Where is the spinal cord white matter thickest?
At the cervical levels because most ascending fibers have already entered the cord and most descending fibers have not yet terminated on their targets.
32
Motor neurons send their axons out of the spinal cord via _______.
ventral nerve root filaments
33
Where is the spinal cord matter thinnest?
The sacral level
34
What supplies the spinal cord with blood?
One anterior artery and two posterior arteries
35
What are the two main arteries from which the anterior artery and two posterior arteries branch out?
vertebral artery and spinal radicular arteries
36
What do the anterior artery and two posterior arteries combine to form?
the spinal artery plexus, which surrounds the spinal cord
37
Vulnerable zone
The mid thoracic region (T4-T8) between that lies between the lumbar and vertebral arterial supplies wherein there is relatively decreased perfusion.
38
What region is most susceptible to infarction during thoracic surgery or other conditions decreasing aortic pressure?
The vulnerable zone (T4-T8)
39
The anterior spinal artery supplies what part(s) of the spinal cord?
2/3rds of the anterior cord, including the anterior horns and the anterior and lateral white matter columns/tract/funiculi
40
The posterior spinal arteries supply what part(s) of the spinal cord?
Posterior columns and part of the posterior horns
41
What two important structures of the brain participate in feedback loops that project back to the cortex via the thalamus?
Cerebellum & basal ganglia
42
Legions in which circuits can lead to apraxia?
Those involving the association cortices in the supplementary motor area (SMA), premotor cortex, and parietal association cortex, all of which are crucial for planning and formulation of motor activities.
43
____________ carry motor systems output to ____________, located in the spinal cord and brainstem, which then project to muscles in the periphery.
upper motor neurons; lower motor neurons
44
What are the two divisions of the descending motor pathways?
lateral motor systems
| medial motor systems
45
Lateral motor systems
travel in the lateral columns
| synaps on more lateral groups of ventral horn neurons
46
Medial motor systems
travel in the anteromedial spinal cord columns
| synapse on medical ventral horn neurons
47
What do the two lateral motor systems pathways form?
lateral corticospinal tract
| rubrospinal tract
48
What do the lateral corticospinal and rubrospinal tracts control?
movement of the extremities
49
The lateral corticospinal tract is essential for what types of movement?
rapid, dexterous movements
50
What are the 4 major medial motor system tracts?
anterior corticospinal tract
vestibulospinal tract
reticulospinal tract
tectospinal tract
51
What do the four medial motor system tracts control?
proximal axial (muscles of the trunk) and girdle muscles involved in postural tone, balance, orienting movements of the head and neck, and automatic gait-related movement
52
Which way do the lateral motor systems pathways descend, ipsilaterally or contralaterally?
contralaterally, thereby controlling the contralateral extremeties
53
Which way do the medial motor systems pathways descend, ipsilaterally or contralaterally?
ipsilaterally/bilaterally
54
Which two tracts of the medial motor systems pathways extend only to the upper few cervical segments?
rubrospinal tract
| tectospinal tract
55
The medial motor pathways tend to terminate on what?
Interneurons that project to both sides of the spinal cord, controlling movements that involve numerous bilateral spinal segments
56
Unilateral lesions of the medial motor systems produce what?
No obvious deficits
57
Lesions to the lateral corticospinal tract produce what?
dramatic motor deficits
58
Which of the lateral tracts is the most clinically important descending motor pathway in the nervous system?
Lateral corticospinal tract
59
Internal capsule
area of white matter in the brain
contains both ascending and descending motor pathways
shaped like V when cut transversly
Separates the caudate nucleus and the thalamus from the caudate nucleus and the globus pallidus
60
Corona radiata
White matter sheet that continues ventrally as the internal capsule and dorsally as the centrum semiovale
Contains both ascending and descending fibers that carry nearly all of the neural traffic from and to the cerebral cortex
Associated with the corticospinal tract, corticopontine tract, and the corticobulbar tract
61
The _____ and _____ are always lateral to the internal capsule.
putamen and globus pallidus
62
The _____ and _____ are always medial to the internal capsule.
caudate nucleus and thalamus
63
What are the 3 parts of the internal capsule?
anterior limb
posterior limb
genu
64
The anterior head of the internal capsule separates which structures?
the head of the caudate nucleus from the putamen and globus pallidus
65
The lateral head of the internal capsule separates which structures?
thalamus from the globus pallidus and putamen
66
Which tract lies in the posterior limb of the internal capsule?
corticospinal tract
67
Fibers projecting from the cortex to the brainstem, including motor fibers for the face, are called _____.
corticobulbar (because they project from the cortex to the brainstem aka "bulb")
68
The continues into the midbrain _________.
cerebral peduncles
69
Basis pedunculis
White matter located in the anterior portion of the cerebral peduncles
70
The middle 1/3rd of the basis pedunculis contains fibers from which two tracts?
Corticobulbar and corticospinal (the other portions of the basis pedunculis contains the corticopontine fibers)
71
The corticospinal tract is also known as:
The pyramidal tract
72
About 85% of the pyramidal tract fibers cross over in the _______________ to enter the lateral white matter columns of the spinal cord.
pyramidal decussation
73
Corticospinal fibers descend from the cerebral peduncles through the ventral pons and collect on the ventral surface of the medulla to form what structure?
The medullary pyramides
74
After the fibers cross in the pyramids, they enter what structure?
The cervical spinal cord as the lateral corticospinal tract.
75
The axons of the corticospinal tract enter the spinal cord central gray matter to synapse onto what?
anterior horn cells
76
What happens to the remaining 15% of corticospinal fibers that do not cross in the medulla?
They continue into the spinal cord ipsilaterlly and enter the anterior white matter columns to form that anterior corticospinal tract.
77
T or F: The autonomic nervous system only contains afferent pathways.
False! The ANS only contain EFFERENT pathways.
78
What are the two main division of the autonomic nervous system?
Sympathetic
| Parasympathetic
79
What is the sympathetic ANS also known as?
thoracolumbar division
80
What is the parasympathetic ANS also known as?
craniosacral division
81
What is the thoracolumbar/sympathetic division of the ANS mainly involved in?
fight or flight functions (e.g. increased heart rate and blood pressure, bronchodilation, and pupil dilation.
82
What parts of the spine does the thoracolumbar division arise from?
T1 to L2/L3
83
What is the craniosacral/parasympathetic division of the ANS mainly involved in?
rest & digest functions (e.g. increased gastric secretions and peristalsis, slowing down heart rate, decreasing pupil size.
84
What does the craniosacral division arise from?
The cranial nerve nuclei from S2-S4.
85
Where are the preganglionic neurons of the sympathetic division located?
Intermediolateral cell column in the central gray matter of the spinal cord from levels T1 to L2/L3.
86
Paired sympathetic chain ganglia
ganglia of the sympathetic NS
deliver information to body about stress and impending danger
bilaterally symmetrical
run down from cervical to sacral levels on each side of the spinal cord
87
Parasympathetic preganglionic fibers
arise from cranial nerve parasympathetic nuclei and sacral parasympathetic nuclei (S2, S3, & S4)
88
Sympathetic postganglionic neurons primarily release which NT?
NE
89
Parasympathetic postganglionic neurons primarily release which NT?
ACh
90
Sympathetic and parasympathetic are controlled both directly and indirectly by what parts of the brain?
Hypothalamus
Brain stem nuclei (e.g. nucleus solitaris)
amygdala
several regions of the limbic cortex
91
Upper motor neurons project to what?
lower motor neurons located in the anterior horn of the spinal cord
92
What do lower motor neurons project to?
skeletal muscles with the peripheral nervous system
93
What system is analogous to the upper and lower motor neuron system?
The coritcobulbar to the cranial nerve motor nuclei
94
Signs of lower motor neuron lesions
muscle weakness
atrophy
fasciculations
hyporeflexia
95
Signs of upper motor neuron lesions
muscle weakness
spasticity (i.e. combination of increased tone and hyperreflexivity)
possible abnormal reflexes (e.g. Babinski's signs)
96
How might a patient with acute upper motor neuron lesions present?
initially, flaccid paralysis with decreased tone and decreased reflexes may be present that can transform to spastic paresis within hours or even months.
97
The process of localizing motor lesions involves which steps?
choosing the correct motor system level, side, and specific neuroanatomical structures affected.
98
Weakness can be caused by
lesions or dysfunction at any level in the motor system
99
Origin of upper motor neurons
motor region of cortex then down through the CNS via one of 6 pathways (corticospinal, coriticobulbar, colliculospinal, rubrospinal, reticulospinal, vestibulospinal tracts)
100
Pure hemiparesis
One of the most commonly diagnosed forms of hemiparesis
| involves weakness of the face (lower), arm, and leg with no associated sensory deficits
101
What are the location rule-outs for pure hemiparesis?
cortical lesions (b/c that would impact the entire motor strip, likely causing sensory deficits)
spinal cord or medulla (then face would be spared)
Muscle or peripheral nerve (would require coincidental involvement of only one 1/2 of body).
102
What locations should be ruled in for pure hemiparesis?
corticospinal and corticobulbar tracts below the cortex and above the medulla
posterior limb of internal capsul, basis pontis, or middle 1/3rd of cerebral peduncle
103
Side of lesion in hemiparesis
contralateral to weakness
104
Common causes of pure hemiparesis
Lacunar infarct of internal capsule or pons
| occassionally infarct of the cerebral peduncle, but not common
105
Associated features of pure hemiparesis
upper motor neuron signs (muscle weakness, spasticity, possible abnormal reflexes)
dysarthria
ataxia on affected side
106
What locations should be ruled out in unilateral paresis of the face and arm without associated somatosensory deficits?
muscular/peripheral nerve damage
| lesions at internal capsule and or below (uncommon, but not impossible)
107
Why should lesions at the internal capsule or below be ruled out in unilateral paresis of the face and arm?
Because the corticobulbar ad corticospinal tracts are very compact in those areas and would therefore likely result in leg involvement in most lesions.
108
What locations should be ruled-in for unilateral paresis of the face and arm without associated somatosensory involvement?
Face and arm areas of the primary motor cortex (lateral regions of the temporal lobe closest to the central sulcus)
109
What side would you expect the lesion to be on in unilateral paresis of face and arm without associated somatosensory deficits?
Contralateral to the affected side (above the pyramidal decussation).
110
What is the most common cause of unilateral face and arm paresis without associated somatosensory deficits?
classic cause =middle cerebral artery superior division infarct
other lesions
tumor
abscess
111
Associated features of unilateral paresis of face and arm without associated somatosensory deficits
upper motor neuron signs
| dysarthria
112
What might you expect if a lesion in the face and arm areas of the motor cortex is in the dominant hemisphere?
Broca's aphasia
| aphemia (pure motor speech disorder)
113
When might you expect to see associated somatosensory deficits in a patient with a lesion to the primary motor cortex?
when the lesion extends to the parietal lobe
114
What is bilateral arm paresis also known as?
brachial diplegia
115
What locations would be ruled out in bilateral arm paresis?
corticospinal tracts (would result in face and leg involvement as well)
116
What areas are ruled-in in bilateral arm paresis?
medial fibers of both lateral corticospinal tracts
bilateral cervical spine ventral horn cells
peripheral nerve or muscle disorders affecting both arms
117
What are the associated features allowing for further localization in bilateral arm paresis?
presence of a central cord or anterior cord syndrome
118
Anterior cord syndrome
Caused by infarction of the anterior portion of spinal cord
119
Central cord syndrome
Most common form of incomplete cord injury
| characterized by impairment in the arms and hands and to a lesser extent in the legs
120
Brown-Séquard Syndrome
incomplete spinal cord lesions reflecting hemisection of spinal cord, often in cervical cord region
121
Symptoms of Brown-Séquard Syndrome
ipsilateral upper motor neuron paralysis
ipsilateral loss of proprioception
contralateral loss of pain and temperature sensation
122
Symptoms of Central Cord Syndrome
paralysis or loss of fine motor control in arms and hands
sensory loss below the site of injury
loss of bladder control
painful sensations
123
Symptoms of Anterior Cord Syndrome
loss of motor function below site of injury
inability to detect temperature and pain
preservation of fine touch and proprioception
124
Common causes of bilateral arm paresis
Central cord syndrome: syringomyelia, intrinsic spinal cord tumor, myelitis
Anterior cord syndrome: anterior spinal artery infarct, trauma, myelitis
Peripheral nerve: bilateral carpal tunnel syndrome of disc herniation
125
Gait disorders (causes)
abnormal function of almost any part of the nervous system
| some orthopedic conditions
126
Problems with _____ are one of the most sensitive indicators of subtle neurological dysfunction.
gait
127
Multiple Sclerosis
autoimmune inflammatory disorder affecting the CNS myelin of unknown etiolgy
128
T or F: Myelin in the PNS (Schwann cells) are not affected in multiple sclerosis.
T, only CNS myelin is affected (oligodendrocytes)
129
What is believed to be the mechanism underlying MS?
Evidence suggests that T lymphocytes may be triggered by a combination of genetic and environmental factors to react against oligodendrocytic myelin.
130
Sclerotic glial scars
Scars left behind from discrete plaques of demyelination and inflammatory response that reoccur in MS.
131
Demyelination causes what?
slowed conduction velocity and ultimately conduction blockage
132
Classical definition of multiple sclerosis
two or more deficits separated in neuroanatomical space and time
133
Clinical diagnosis of MS is based:
presence of typical clinical features
MRI evidence of white matter lesions
slowed conduction velocities on evoked action potentials
presence of oligoclonal bands in CSF on lumbar puncture
134
What MRI findings suggest MS?
multiple T2-bright areas representing demyelination plaques located in white matter
135
About 50% of patients presenting with a single episode of ________ and _________ subsequently develop MS.
optic neuritis; transverse myelitis
136
What are the courses of MS?
relapsing-remitting
progressive
combination of relapsing-remitting & progressive
137
Median survival from time of MS onset
25-35 years
138
Current drug therapies for MS
interferon beta
| high-dose steroids
139
Common associated symptoms of MS requiring multidisciplinary treatment
```
spasticity
pain
extreme fatigue
impaired bowel, bladder, and sexual function
diplopia
dysphagia
psychiatric manifestations
```
140
Motor neuron diseases
several uncommon disorders that can selectively affect upper motor neurons, lower motor neurons, or both, producing motor deficits without sensory abnormalities or other findings.
141
Examples of motor neuron diseases
Amyotophic lateral sclerosis (ALS) (both)
Primary lateral sclerosis (upper motor neurons)
Spinal muscular atrophy (lower motor neurons)
142
What does ALS stand for?
Amyotrophic lateral sclerosis
143
ALS is characterized by
gradual progressive degeneration of both upper and lower motor neurons, leading eventually to respiratory failure and death
144
T or F: Most cases of ALS are inherited.
F; Most cases occur sporadically, but there are also inherited forms.
145
What are the initial symptoms of ALS?
weakness or clumsiness typically beginning focally and then spreading to adjacent muscle groups.
146
Symptoms of ALS
muscular paresis
painful muscle cramps
fasciculations (sometimes best seen in tongue)
bulbar symptoms (dysarthria, dysphagia, respiratory problems)
psuedobulbar affect
147
How might a patient with ALS present during a neurological exam?
- evidence of upper motor neuron damage such as increased tone and brisk reflexes
- evidence of lower motor neuron damage such as atrophy and fasciculations (sometimes best seen in tongue)
- intact sensory and mental status
148
What is the median survival from time of ALS onset?
23-52 months
149
What are important differential diagnoses when assessing for ALS?
```
lead toxicity
thyroid dysfunction
dysproteinemia
vitamin B12 deficiency
vasculitis
panneoplastic syndromes
multifocal motor neuropathy with conduction block
```
150
Panneoplastic syndrome
syndrome that indirectly results from the presence of cancer in the body
most commonly associated with cancers of the lung, breast, ovaries, or lymphatic system
151
Vasculitis
inflammation of blood vessels resulting
152
The corticospinal tracts can be grouped together into what 3 large (& most important) categories:
1) lateral corticospinals - motor
2) dorsal column/medial lemniscus - somatosensory
3) spinothalamics - pain & tempertaure (as the representative for all the ventrolateral system)
