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Neuro Part 2 > Week 5.1 > Flashcards

Week 5.1 Flashcards

1
Q

What are the benefits of using intracellular methods to record the electrophysiology of neurons?

A
  • precise measurements of a single axons

- insight into ionic mechanisms responsible for membrane potential

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2
Q

How does nerve conduction relate to diameter?

A

directly proportional

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3
Q

What are the constants for the relationship between axon diameter and conduction velocity for myelinated and unmyelinated axons?

A
  • myelinated: 6

- unmyelinated: 1.7

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4
Q

How do the amplitudes of extracellular and intracellular APs vary with neuronal cell size?

A
  • intracellular don’t vary with size

- extracellular increases with increasing cell size

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5
Q

In what order are neurons recruited by an artificial electrical stimulation?

A

largest to smallest

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6
Q

In what order are neurons recruited by a natural electrical stimulus?

A

smallest to largest

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7
Q

Name five properties of neurons that vary with axon diameter.

A
  • conduction velocity
  • amplitude of extracellularly recorded action potentials
  • order of artificial activation (inverse)
  • order of natural activation
  • principles of anesthesia
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8
Q

What form of anesthesia affects smaller diameter axons first?

A

local anesthetics

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9
Q

Name four forms of anesthesia that affect larger axons first.

A
  • temperature
  • compression
  • positive charge (anodal block)
  • asphyxia/anoxia
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10
Q

Compound action potentials are the result of what electrophysiologic principle?

A

differing conduction velocities for axons of different sizes

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11
Q

How does a compound AP recording vary with distance form the stimulus?

A

the closer you are, the less separation there is between peaks

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12
Q

How does stimulus intensity affect the shape of an intracellular and extracellular AP?

A
  • doesn’t affect intracellular because it’s an all or nothing event
  • extracellular show increased amplitude and number of peaks
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13
Q

A-alpha fibers carry what information?

A

muscle spindle and GTO afferents

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14
Q

A-beta fibers carry what information?

A
  • secondary muscle spindle

- skin touch and pressure

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15
Q

A-delta fibers carry what information?

A
  • skin touch
  • temperatura
  • fast pain
  • autonomic afferents
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16
Q

C fibers carry what information?

A
  • autonomic afferents
  • temperature
  • slow pain
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17
Q

Which fiber type is most common in the dorsal root?

A

most C fibers, equal numbers of the others

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18
Q

What fiber types are found in the ventral root?

A
  • A-alpha (LMN)
  • A-gamma
  • B (autonomic preganglionics)
  • C (ventral root sensory axons)
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19
Q

What are B fibers in the dorsal root?

A

autonomic preganglionics

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20
Q

What are C fibers in the dorsal root?

A

ventral root sensory axons

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21
Q

What is the Bell-Majendie Law?

A

states that all sensory axons enter via the dorsal root and all motor neurons exit via the ventral root

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22
Q

What is the one exception to the Bell-Majendie Law?

A

group C fibers from pelvic viscera at L5-S3 with a DRG cell body but enter the spinal cord via the ventral root

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23
Q

Why does transection of the dorsal root not always eliminate pain from that dermatome?

A

because some C fibers enter the spinal cord through the ventral root

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24
Q

What three waves might you see during a motor nerve conduction study?

A
  • M wave
  • F wave
  • H reflex
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25
Q

Which is seen in a motor nerve conduction study after maximal stimulus: M wave, F wave, or H reflex?

A

M wave and F wave

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26
Q

What is orthodromic?

A

means in the physiologic or normal direction

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27
Q

Why can most people not just raise half their forehead?

A

because the LMNs for the forehead receive bilateral UMN innervation in contrast to lower motor neurons for the lower face which receive unilateral innervation

28
Q

How does -paresis differ from -plegia?

A
  • paresis describes partial paralysis

- plegia describes no movement at all

29
Q

What is paraplegia?

A

the inability to move both legs

30
Q

How is muscle strength graded?

A

5: full strength
4: gravity + resistance
3: antigravity
2: joint movement
1: visible contraction
0: no contraction

31
Q

How are muscle stretch reflexes graded?

A

0: no reflex
1: reflex only with reinforcement
2: normal
3: brisk
4: clonus

32
Q

How can you assess muscle tone in clinic?

A

by passively moving the limb and judging resistance

33
Q

Where could a lesion be located that would cause UMN signs in the face and leg?

A

it would have to be multiple lesions

34
Q

Where could you find lesion that causes paraparesis?

A
  • thoracic spinal cord affecting both UMN tract

- parasagittal region (ACA stroke)

35
Q

If someone has generalized LMN weakness, the addition of numbness tells you what?

A

it is a peripheral neuropathy (afferents are being affected too)

36
Q

If someone has LMN weakness and deep tendon reflexes are affected, what does this tell you?

A

that the lesion is localized to the anterior horn cell or peripheral nerve, not at the NMJ or in the muscle

37
Q

Processes that cause generalized LMN weakness with normal sensation and deep tendon reflexes are typically located where?

A

the NMJ or muscle

38
Q

What is motor neuron disease?

A

a generic term (aka ALS) used to describe a disease process that affects both UMNs and LMNs

39
Q

ALS affects which cell population?

A

both upper and lower motor neurons

40
Q

What are the primary features of ALS?

A
  • bilateral, asymmetric weakness
  • UMN and LMN signs
  • normal sensation
  • bulbar dysfunction (dysarthria or dysphagia)
41
Q

What is dysarthria?

A

a motor speech disorder

42
Q

How can you distinguish between a LMN problem that affects the NMJ or the muscle itself?

A

creatine phosphokinase typically elevated if problem is with the muscle

43
Q

What signs and symptoms would point you to believe someone with generalized motor weakness had a myopathy?

A
  • proximal weakness
  • elevated CPK
  • normal EMG
44
Q

When there is diffuse muscle weakness, how can we localize it to the anterior horn cell, peripheral nerve, NMJ, or muscle?

A
  • anterior horn cell: diminished reflexes, no numbness
  • peripheral nerve: diminished reflexes and numbness
  • NMJ: reflexes intact and CPK normal
  • muscles: reflexes intact and CPK elevated
45
Q

Antibodies target what in those with myasthenia gravis?

A

nicotinic AChRs or associated proteins

46
Q

Describe the weakness that affects those with myasthenia gravis.

A
  • fluctuating
  • improves with rest
  • propensity for extra-ocular muscles
47
Q

What kind of inhibition occurs at the NMJ in those with myasthenia gravis?

A

competitive inhibition

48
Q

The pathophysiology of myasthenia gravis depends on what two processes?

A

competitive inhibition and inflammatory changes

49
Q

Myasthenia gravis typically affects those of what age?

A

those in their 20s and 50s

50
Q

What gender differences are their in the onset of myasthenia gravis?

A
  • early onset more common in females

- later onset more common in males

51
Q

Describe the motor symptoms of of myasthenia gravis.

A
  • ocular: diplopia, ptosis
  • bulbar: dysarthria, dysphagia, dyspnea
  • extremities: proximal weakness and head drop
52
Q

What is ptosis?

A

eyelid droop

53
Q

All new myasthenia gravis patients get checked for what other condition?

A

thymoma

54
Q

Which myasthenia gravis patients are most likely to also have a thymoma?

A

those with onset after the age of 30

55
Q

The most specific test for myasthenia gravis is what?

A

AChR antibody testing

56
Q

The most sensitive test for myasthenia gravis is what?

A

single-fiber EMG

57
Q

What is an endrophonium test?

A
  • test for myasthenia gravis in which you block AChE and look to see if the patient transiently improves
  • requires an objective measure like degree of ptosis
58
Q

How does repetitive stimulation work as a diagnostic test for those with myasthenia gravis?

A

repeated stimulation depletes ACh stores and the amplitude of the extracellular AP will decrease only in those with myasthenia gravis

59
Q

What are the cons of single-fiber EMG testing for myasthenia gravis?

A

it is painful and difficult to place the electrode

60
Q

How is single-fiber EMG performed to test for myasthenia gravis?

A
  • measure single muscle fiber action potentials from two in the same motor unit
  • variability in the timing of the firing suggests myasthenia gravis
61
Q

The mainstay therapy for myasthenia gravis is what?

A

immunosuppression (steroids)

62
Q

What is pyridostigmine?

A

an AChE inhibitor with a long half life used in to treat myasthenia gravis before the advent of steroids

63
Q

What time course can a patient with myasthenia gravis expect when they begin corticosteroids?

A
  • transient worsening
  • improvement between 2 and 6 weeks
  • maximal effect at 6 months
  • remission is steroid dependent
64
Q

Which chemotherapy drugs are effective in the treatment of myasthenia gravis?

A
  • azathioprine
  • cyclosporine
  • cyclophosphamide
65
Q

Name five medical therapies for myasthenia gravis.

A
  • steroids
  • anticholinesterases (pyridostigmine)
  • chemotherapy (azathioprine, cyclosporine, cyclophosphamide)
  • IVIG
  • plasmapheresis
66
Q

What are the indications for plasmapheresis in patients with myasthenia gravis?

A
  • myasthenic crisis
  • severe exacerbation
  • pre-thymectomy
67
Q

What are the main pro and con of thymectomy in the treatment of myasthenia gravis?

A
  • demonstrate significant improvement

- major surgery

Neuro Part 2 (18 decks)

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