Basic Neuroanatomy II: The Spine Flashcards

(87 cards)

1
Q

The Left Brain-Right Body role holds for most somatic neural pathways EXCEPT _____.

A

The Left Brain-Right Body role holds for most somatic neural pathways EXCEPT the cranial nerves

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2
Q

Corticospinal tracts

A

The corticospinal tracts send motor information from the cortex to the spinal cord as the name suggests.

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3
Q

Anterolateral (or spinothalamic) tracts and dorsal (or posterior) column pathways

A

Bring sensory input from the spinal cord to the brain by way of the brainstem. The names of these pathways refer to their anatomic positions within the spinal cord.

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4
Q

“Pyramidal system”

A

Another name for the corticospinal tracts, as they travel for part of their course in the medullary pyramids

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5
Q

“Extrapyramidal system”

A

Includes the basal ganglia and cerebellum, which participate in circuits with the motor cortex and are involved in action initiation and coordination

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6
Q

Location of the motor cortex in the brain

A
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7
Q

Structure and location of the midbrain

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8
Q

Decussation

A

Crossing from one side of the body to the other, as a motor nerve does

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9
Q

Pathway of a motor signal via the pyramidal system

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10
Q

Upper vs lower motor neurons

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11
Q

Lesions above the ___ in motor pathways cause ___ weakness. Lesions below the ___ in motor pathways cause ___ weakness.

A

Lesions above the cervicomedullary junction in motor pathways cause contralateral weakness. Lesions below the cervicomedullary junction in motor pathways cause ipsilateral weakness.

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12
Q

Mnemonic for upper vs lower motor neuron pathology

A

Upper motor neuron damage makes things go up,

Lower motor neuron damage makes things go down

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13
Q

Upper motor neuron signs may ____ in an acute setting.

A

Upper motor neuron signs may not be present in an acute setting.

They take time to emerge, coming out over days to weeks following an acute upper motor neuron lesion. In the interim, the innervated muscles will be flacid and areflexive.

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14
Q

The motor cortex does NOT control movement of the ___.

A

The motor cortex does NOT control movement of the facial muscles or autonomicly/enterically regulated muscles.

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15
Q

Lower motor neurons begin in the ___ of the spinal tract.

A

Lower motor neurons begin in the anterior horns of the spinal tract.

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16
Q

Motor and somatosensory cortex homunculi

A
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17
Q

Babinski’s sign reappears when there is damage to the ___ neuron innervating the foot.

A

Babinski’s sign reappears when there is damage to the upper motor neuron innervating the foot.

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18
Q

Hoffman’s sign

A

Sort of a Babinski sign for the upper extremity – a sign of upper motor neuron dysfunction.

To see if a Hoffmann sign is present, the examiner holds the patient’s hand by the middle finger with one hand, and uses the other hand to quickly flick the tip of the middle finger (as if snapping one’s fingers, but with the patient’s finger between). If a Hoffmann sign is present, the fingers and thumb will flex.

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19
Q

Pronator drift

A

When the arms are held outstretched with the palms up and fingers spread (as if holding a tray), the hand may begin to close and the arm may begin to pronate and drift downward if upper extremity weakness is due to parietal lobe (proprioception) or upper motor neuron pathology

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20
Q

When an upper motor neuron causes weakness without full paralysis, a distinct pattern of ____ in the upper extremities and ____ in the lower extremities may be observed.

A

When an upper motor neuron causes weakness without full paralysis, a distinct pattern of extensor weakness relative to flexors in the upper extremities and flexor weakness relative to extensors in the lower extremities may be observed.

In other words, the arm is stronger when flexing the elbow compared to extending the elbow, and the leg is stronger when extending the knee compared to flexing the knee.

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21
Q

Posture of a patient with long-standing upper motor neuron injury (e.g., prior stroke)

A

The arm, wrist, and fingers are flexed and pronated close to the body, whereas the lower extremity is extended at the knee with the foot plantarflexed and needs to be circumducted when the patient walks.

This posture demonstrates flexor dominance in the upper extremity and extensor dominance in the lower extremity

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22
Q

Upper motor neuron pathology signs that DO present acutely

A
  • Pronator drift
  • “Post-stroke” posture (flexion of upper extremity joints, extension of lower extremity joints)
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23
Q

Radial nerve palsy

A

Note that a radial nerve palsy will affect the triceps, wrist/finger extensors, and supinator, and can thus mimic an upper motor neuron lesion (resting arm flexion) and vice versa

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24
Q

Corticobulbar tracts

A

The tract of the upper motor neurons of the face, tongue, larynx, and pharynx.

Corticobulbar fibers terminate in their respective cranial nerve nuclei in the brainstem. The lower motor neurons arise in the cranial nerve nuclei and travel in the cranial nerves.

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25
Organs of proprioception
Golgi tendon organs and muscle spindles
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Corticospinal tract, dorsal column pathway, and anterolateral tract
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"Sorting" of sensory signals
* **Pain and temperature** information enters the **anterolateral tracts** (also known as the spinothalamic tracts) * **Proprioception and vibration** information enters the **dorsal columns** * **Light touch information** travels to some extent in **both pathways** and, therefore, has less localizing value. * **Both sensory pathways** ascend through the spinal cord and brainstem to **arrive at the ventral posterior lateral (VPL) nucleus** of the thalamus
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Crossing of sensory pathways en route to the brain
The crossing of the dorsal column system **occurs in the medulla**, just superior to the crossing of the corticospinal tracts (which cross at the cervicomedullary junction). Therefore, unilateral lesions of the dorsal column pathway from the **upper medulla and superiorly** (i.e., pons, midbrain, thalamus, subcortical white matter, somatosensory cortex) affect **contralateral** sensation, whereas unilateral lesions from the **lower medulla through the spinal cord** affect **ipsilateral** sensation
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Location of the somatosensory cortex
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Dorsal column pathway
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Unlike other neural pathways, the anterolateral/spinothalamic tract decussates \_\_\_\_.
Unlike other neural pathways, the anterolateral/spinothalamic tract decussates **as it enters the spinal cord**, and thus **travels the entire length of the spinal cord on the contralateral side of the body.**
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Anterolateral pathway
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Main anatomical differences between anterolateral and dorsal column pathways
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Dissociated somatosensory deficits in localizing the level of a spinal lesion (aka Hemicord syndrome or Brown-Sequard syndrome)
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Dysfunction in the dorsal column pathway leads to deficits in \_\_\_\_
Dysfunction in the dorsal column pathway leads to deficits in **vibration sense and proprioception**
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Fasciculus cuneatus vs fasciculus gracilis
The **fasiculi cuneatus** run **laterally** in the dorsal columns and carry **upper extremity sensory information**, whereas the **fasciculi gracilis** run **medially** in the dorsal columns and carry **lower extremity sensory information**. Rise all the way to the **lower medulla** where they **synapse in the nucleus cuneatus and nucleus gracilis** on each side and **_cross at this level_** via the **internal arcuate fibers** to become the contralateral **medial lemniscus**, which proceeds on to the VPL nucleus.
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Dorsal column pathway schematic
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Isolated dorsal column pathway dysfunction is most commonly due to:
* large fiber peripheral neuropathy * dorsal root ganglionopathy * spinal cord disease
39
Simple test of proprioception
Proprioception is tested by **moving a particular joint up or down** and asking the patient to **determine if the joint has been moved up or down without looking** Note that, partially due to the limited avaiability of good joints to test on, **sensitivity of proprioception tests is not as high as vibration tests** for detecting dorsal column pathway dysfunction.
40
Pseudoathetosis
Upon Romberg's test, patients do not exhibit Romberg sign, but instead exhibit **involuntary piano playing–like movements of the toes**
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Romberg's sign
Upon Romberg's test, patient will **sway and take a step to maintain balance**
42
Anterolateral pathway schematic
43
Isolated diminished pain sensation can be due to:
* peripheral neuropathy (affecting small fibers) * radiculopathy * dysfunction in the anterolateral system in the spinal cord
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Testing for pain sensation
The "pin prick" test is used here. Exactly what it sounds like. Prick directly along the spine. Patients will note a discrete level above which the pin is felt as sharp and below which it is felt as dull (or not felt)
45
Testing for temperature sensation
Temperature can be assessed by using the **side of a metal tuning fork** to see if it feels **equally cold in different locations**
46
Facial sensation is provided by. . .
. . . **the trigeminal nerve**, and thus has different characteristics than spinal sensory nerve pathways.
47
Weakness can occur due to lesions . . .
. . . anywhere in the motor pathways: brain, brainstem, spinal cord, ventral roots, peripheral nerves, neuromuscular junction, and/or muscles.
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Clinical evaluation of weakness and somatic sensory deficit
The clinical evaluation of weakness or sensory disturbances requires determining the **distribution** of the patient’s symptoms and the **time course** of the onset and evolution of the patient’s symptoms.
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Pattern of motor and sensory deficits in the face and hand on one side
Since the face and arm are adjacent on the cortical surface, they share a vascular supply in the form of the middle cerebral artery. Thus, **ischemia or infarction due to pathology of the middle cerebral arteries** often causes this pattern of deficits.
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Cheiro-oral pattern
Since the hand and the the mouth are among the most sensitive and dexterous, they have substantial cortical representation. Therefore, the **symptom of sensory changes and/or weakness in the hand and ipsilateral perioral region** is highly suggestive of a **lesion in the contralateral cerebral hemisphere.**
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Agraphesthesia
Inability to recognize a number or letter drawn on the hand
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Extinction to double simultaneous stimulation
When the patient’s **left and right sides of the body are touched simultaneously,** the patient may **not note the sensation in the limb contralateral to the lesion**, **_despite_** being **able to detect sensation when this limb is touched in isolation**
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Crossed sign
Caused by **unilateral brainstem lesions**: weakness and/or sensory changes in the **ipsilateral face**, but in the **contralateral body**
54
Involvement of the spinal cord is usually ___ in pattern because \_\_\_.
Involvement of the spinal cord is usually **bilateral** in pattern because **the thing is so damn small that whatever affects one side often affects the other.** However, it is of course possible to have unilateral intramedullary or extramedullary pathology, often from **unilateral compression** o**r unilateral dorsal root ganglia pathology** (ie, **herpesviridae, specifically VZV**)
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Patterns of sensory weakness -- name them
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Most common cause of sudden-onset weakness and/or sensory changes localizing to the brainstem
Stroke
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Common causes of sudden-onset weakness and/or sensory changes localizing to the spinal cord
* Acute disk prolapse * Vertebral collapse (trauma or malignancy)
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Sudden-onset weakness and/or sensory changes localizing to a particular nerve may be caused by . . .
. . . a nerve infarct (as can be seen in vasculitic neuropathies)
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Acute- to subacute-onset weakness and/or sensory changes at any level of the nervous system can be due to:
* Inflammatory conditions (Guillain-Barré syndrome) * Transverse myelitis * Acute demyelinating lesion in MS * Infection (often cerebral or epidural abscess)
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Subacute- to chronic-onset weakness and/or sensory changes can be caused by:
* Neoplasm * Chronic disease * Inflammation (chronic inflammatory demyelinating polyneuropathy) * Degenerative disease
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Internal capsule
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Axial spinal cord section showing location of nervous pathways
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Lamination refers to \_\_\_
Lamination refers to **the arrangement of fibers within a pathway ​**
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The corticospinal, dorsal column, and anterolateral pathways side-by-side
A: Corticospinal B: Dorsal column C: Anterolateral/Spinothalamic
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As a general rule, the more peripheral an axon in a spinal tract is, the more distal its site of innervation. Why is this the case?
Because the gray matter is in the center of the spine, and so proximal nerves need to be closer to the gray matter so they can synapse on lower neurons at the appropriate level.
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Lamination of the corticospinal, dorsal column, and anterolateral tracts
The corticospinal and anterolateral tracts are arranged with the upper extremities medial, lower extremities lateral. The dorsal column tract is arranged with the lower extremities medial, upper extremities lateral. **This breaks the general rule for arrangement because the dorsal column pathway traverses the spinal cord without decussating until it reaches the medulla.**
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Hemicord syndrome (aka Brown-Sequard syndrome)
* Affects all pathways on **one side** of the spinal cord * A unilateral spinal cord lesion will cause **ipsilateral weakness, ipsilateral proprtioception and vibration deficits**, and **contralateral pain and temperature sensation deficits** * A small region of ipsilateral pain and temperature sensation loss may also be seen at the levels over which the pathway is crossing * Most commonly caused by penetrating trauma, but may be due to a unilateral demyelinating lesion or unilateral mass effect (from a malignancy, Pott's disease, etc)
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Anterior Cord Syndrome
* Involves most of the spinal cord but spares the dorsal columns * **Bilateral motor function, pain, and temperature sensation are lost**, but sense of **vibration and proprioception are maintained** below the level of the lesion. * Both **upper and lower motor neuron** signs may be seen * Most commonly due to **infarction in the territory of the anterior spinal artery** of the spinal cord * Caused by abdominal aortic aneurysm (AAA), AAA rupture, or in the setting of surgery for AAA repair.
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Central Cord Syndrome
* Affects the area of the **anterior commisure**, where the anterolateral tracts cross as they enter * **Bilateral loss of pain and temperature sensation**, which can cause a **“cape-like” distribution** of sensory deficits * Most commonly due to **syrinx**, a dilatation of the central canal of the spinal cord. * Usually occurs in the **cervical spinal cord** * **​For this reason, upper extremity (which is innervated by cervical nerves) is usually affected first**
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Subacute combined degeneration
* Selective involvement of the dorsal columns and corticospinal tracts * Most commonly caused by **vitamin B12 deficiency**, but can be caused by **copper deficiency** * Both result in concurrent **myelopathy and neuropathy** which can cause **mixed upper and lower motor neuron features on examination**
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Ddx for copper deficiency
Can occur in the setting of **excess zinc ingestion** (which can be caused by zinc-containing denture creams), after **gastric bypass surgery**, or due to **malabsorption.**
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A 66-year-old male patient with a history of smoking, hyperlipidemia and hypertension has a stroke causing damage to the right internal capsule. Where do you expect to find weakness on neurologic examination?
Left face, left arm and leg
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Omega sign
Used to identify the location of the hand in the motor cortex
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Centrum semiovale
Where motor axons travel, just lateral to the ventricles and superior to the internal capsule
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Cerebral peduncles
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Arterial supply to the internal capsule
Anterior choroidal artery
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The combination of weakness and cranial nerve deficits suggests a lesion at the level of \_\_\_.
The combination of weakness and cranial nerve deficits suggests a lesion at the level of **the midbrain**
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When someone presents with bilateral leg weakness, you should ask about. . .
. . . urination and bowel movement patterns!
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Patient presents with weakness in the posterior aspect of the hand and arm as well as extensor weakness and absent brachioradialis reflex. He reports that he had woken up with these symptoms after having slept heavily with his arm behind his back following a night out. What is the likely diagnosis?
Radial nerve damage
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Radial nerve is the BEST
**B**rachioradialis **E**xtensors **S**upinator **T**riceps
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Two locations where you can have a pure motor stroke
Pons and the internal capsule
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Intermediolateral nuclei
Only exist in the thoracic and upper lumbar spinal cord. Gives rise to the sympathetic innervation of autonomics, controlling blood pressure and other autonomic features.
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"Graceful like a leg"
The gracilis carries dorsal tract sensory information from the legs
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Dorsal column decussation
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Bilateral involvement of the corticospinal tract and anteriolateral tract with sparing of the dorsal column suggests. . .
. . . **anterior infarct from loss of the anterior spinal arteries.**
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Patient presents with bilateral, isolated pain and tempetature loss of just the upper extremities. What does this pattern suggest?
Early central cord syndrome. **JUST** the upper limb anterolateral tract is affected at first, due to the central crossing of the anterolateral tract and the fact that central cord syndrome predominates in the cervical spine. If the disease progresses, it will also begin to affect other senses, motor control. etc.
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For whatever reason, ____ tend to affect the dorsal column specifically and then spread to the corticospinal tract in advanced stages.
For whatever reason, **B12 deficiency, copper deficiency, and neurosyphilis** tend to affect the dorsal column specifically and then spread to the corticospinal tract in advanced stages.