Basic Neuroanatomy II: The Spine

Question 1

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

Answer 1

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

Question 2

Corticospinal tracts

Answer 2

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

Question 3

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

Answer 3

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.

Question 4

“Pyramidal system”

Answer 4

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

Question 5

“Extrapyramidal system”

Answer 5

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

Question 6

Location of the motor cortex in the brain

Answer 6

Question 7

Structure and location of the midbrain

Answer 7

Question 8

Decussation

Answer 8

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

Question 9

Pathway of a motor signal via the pyramidal system

Answer 9

Question 10

Upper vs lower motor neurons

Answer 10

Question 11

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

Answer 11

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

Question 12

Mnemonic for upper vs lower motor neuron pathology

Answer 12

Upper motor neuron damage makes things go up,

Lower motor neuron damage makes things go down

Question 13

Upper motor neuron signs may ____ in an acute setting.

Answer 13

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.

Question 14

The motor cortex does NOT control movement of the ___.

Answer 14

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

Question 15

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

Answer 15

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

Question 16

Motor and somatosensory cortex homunculi

Answer 16

Question 17

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

Answer 17

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

Question 18

Hoffman’s sign

Answer 18

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.

Question 19

Pronator drift

Answer 19

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

Question 20

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.

Answer 20

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.

Question 21

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

Answer 21

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

Question 22

Upper motor neuron pathology signs that DO present acutely

Answer 22

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

Question 23

Radial nerve palsy

Answer 23

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

Question 24

Corticobulbar tracts

Answer 24

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.

Question 25

Organs of proprioception

Answer 25

Golgi tendon organs and muscle spindles

Question 26

Corticospinal tract, dorsal column pathway, and anterolateral tract

Answer 26

Question 27

“Sorting” of sensory signals

Answer 27

• 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

Question 28

Crossing of sensory pathways en route to the brain

Answer 28

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

Question 29

Location of the somatosensory cortex

Answer 29

Question 30

Dorsal column pathway

Answer 30

Question 31

Unlike other neural pathways, the anterolateral/spinothalamic tract decussates ____.

Answer 31

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.

Question 32

Anterolateral pathway

Answer 32

Question 33

Main anatomical differences between anterolateral and dorsal column pathways

Answer 33

Question 34

Dissociated somatosensory deficits in localizing the level of a spinal lesion

(aka Hemicord syndrome or Brown-Sequard syndrome)

Answer 34

Question 35

Dysfunction in the dorsal column pathway leads to deficits in ____

Answer 35

Dysfunction in the dorsal column pathway leads to deficits in vibration sense and proprioception

Question 36

Fasciculus cuneatus vs fasciculus gracilis

Answer 36

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.

Question 37

Dorsal column pathway schematic

Answer 37

Question 38

Isolated dorsal column pathway dysfunction is most commonly due to:

Answer 38

• large fiber peripheral neuropathy
• dorsal root ganglionopathy
• spinal cord disease

Question 39

Simple test of proprioception

Answer 39

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.

Question 40

Pseudoathetosis

Answer 40

Upon Romberg’s test, patients do not exhibit Romberg sign, but instead exhibit involuntary piano playing–like movements of the toes

Question 41

Romberg’s sign

Answer 41

Upon Romberg’s test, patient will sway and take a step to maintain balance

Question 42

Anterolateral pathway schematic

Answer 42

Question 43

Isolated diminished pain sensation can be due to:

Answer 43

• peripheral neuropathy (affecting small fibers)
• radiculopathy
• dysfunction in the anterolateral system in the spinal cord

Question 44

Testing for pain sensation

Answer 44

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)

Question 45

Testing for temperature sensation

Answer 45

Temperature can be assessed by using the side of a metal tuning fork to see if it feels equally cold in different locations

Question 46

Facial sensation is provided by. . .

Answer 46

. . . the trigeminal nerve, and thus has different characteristics than spinal sensory nerve pathways.

Question 47

Weakness can occur due to lesions . . .

Answer 47

. . . anywhere in the motor pathways: brain, brainstem, spinal cord, ventral roots, peripheral nerves, neuromuscular junction, and/or muscles.

Question 48

Clinical evaluation of weakness and somatic sensory deficit

Answer 48

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.

Question 49

Pattern of motor and sensory deficits in the face and hand on one side

Answer 49

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.

Question 50

Cheiro-oral pattern

Answer 50

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.

Question 51

Agraphesthesia

Answer 51

Inability to recognize a number or letter drawn on the hand

Question 52

Extinction to double simultaneous stimulation

Answer 52

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

Question 53

Crossed sign

Answer 53

Caused by unilateral brainstem lesions:

weakness and/or sensory changes in the ipsilateral face, but in the contralateral body

Question 54

Involvement of the spinal cord is usually ___ in pattern because ___.

Answer 54

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 or unilateral dorsal root ganglia pathology (ie, herpesviridae, specifically VZV)

Question 55

Patterns of sensory weakness – name them

Answer 55

Question 56

Most common cause of sudden-onset weakness and/or sensory changes localizing to the brainstem

Answer 56

Stroke

Question 57

Common causes of sudden-onset weakness and/or sensory changes localizing to the spinal cord

Answer 57

• Acute disk prolapse
• Vertebral collapse (trauma or malignancy)

Question 58

Sudden-onset weakness and/or sensory changes localizing to a particular nerve may be caused by . . .

Answer 58

. . . a nerve infarct (as can be seen in vasculitic neuropathies)

Question 59

Acute- to subacute-onset weakness and/or sensory changes at any level of the nervous system can be due to:

Answer 59

• Inflammatory conditions (Guillain-Barré syndrome)
• Transverse myelitis
• Acute demyelinating lesion in MS
• Infection (often cerebral or epidural abscess)

Question 60

Subacute- to chronic-onset weakness and/or sensory changes can be caused by:

Answer 60

• Neoplasm
• Chronic disease
• Inflammation (chronic inflammatory demyelinating polyneuropathy)
• Degenerative disease

Question 61

Internal capsule

Answer 61

Question 62

Axial spinal cord section showing location of nervous pathways

Answer 62

Question 63

Lamination refers to ___

Answer 63

Lamination refers to the arrangement of fibers within a pathway ​

Question 64

The corticospinal, dorsal column, and anterolateral pathways side-by-side

Answer 64

A: Corticospinal

B: Dorsal column

C: Anterolateral/Spinothalamic

Question 65

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?

Answer 65

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.

Question 66

Lamination of the corticospinal, dorsal column, and anterolateral tracts

Answer 66

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.

Question 67

Hemicord syndrome (aka Brown-Sequard syndrome)

Answer 67

• 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)

Question 68

Anterior Cord Syndrome

Answer 68

• 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.

Question 69

Central Cord Syndrome

Answer 69

• 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

Question 70

Subacute combined degeneration

Answer 70

• 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

Question 71

Ddx for copper deficiency

Answer 71

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.

Question 72

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?

Answer 72

Left face, left arm and leg

Question 73

Omega sign

Answer 73

Used to identify the location of the hand in the motor cortex

Question 74

Centrum semiovale

Answer 74

Where motor axons travel, just lateral to the ventricles and superior to the internal capsule

Question 75

Cerebral peduncles

Question 76

Arterial supply to the internal capsule

Answer 76

Anterior choroidal artery

Question 77

The combination of weakness and cranial nerve deficits suggests a lesion at the level of ___.

Answer 77

The combination of weakness and cranial nerve deficits suggests a lesion at the level of the midbrain

Question 78

When someone presents with bilateral leg weakness, you should ask about. . .

Answer 78

. . . urination and bowel movement patterns!

Question 79

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?

Answer 79

Radial nerve damage

Question 80

Radial nerve is the BEST

Answer 80

Brachioradialis

Extensors

Supinator

Triceps

Question 81

Two locations where you can have a pure motor stroke

Answer 81

Pons and the internal capsule

Question 82

Intermediolateral nuclei

Answer 82

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.

Question 83

“Graceful like a leg”

Answer 83

The gracilis carries dorsal tract sensory information from the legs

Question 84

Dorsal column decussation

Answer 84

Question 85

Bilateral involvement of the corticospinal tract and anteriolateral tract with sparing of the dorsal column suggests. . .

Answer 85

. . . anterior infarct from loss of the anterior spinal arteries.

Question 86

Patient presents with bilateral, isolated pain and tempetature loss of just the upper extremities. What does this pattern suggest?

Answer 86

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.

Question 87

For whatever reason, ____ tend to affect the dorsal column specifically and then spread to the corticospinal tract in advanced stages.

Answer 87

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.