NMJ and Muscle disorders Flashcards Preview

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Flashcards in NMJ and Muscle disorders Deck (59)
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1

what distinguishes a LMN lesion from a UMN one

weakness
low tone
fasiculations

2

what part of spinal cord to motor neurones arise from

ventral horn

3

what do the terminal projections of motor neurones do

give rise to very fine projections that run along the muscle cell
synapse at motor end plate

4

how many motor neurones can a muscle respond to

only one

5

what is between the motor neurone and muscle

synaptic cleft/ gutter

6

describe transmission at the NMJ

Action potential moves along the nerve
Voltage gated calcium channels open allowing influx of calcium
Vesicles of acetyl choline released into synaptic cleft

Acetyl choline diffuses across the synaptic cleft
The acetylcholine receptor opens and renders the membrane permeable to Na / K ions
The depolarisation starts an action potential at the motor end plate

7

what does acetylcholinesterase do

converts acetyl choline in acetate and choline

8

what happens to choline

is sequestered back into presynaptic vesicles

9

what are the main presynaptic NMJ disorders

botulism
lambert eaton myasthenic syndrome
abnormality of calcium/ sodium/ magnesium

10

what causes botulism

clostridium botulinum (organism present in soil- food and wounds can become infected)

11

what does botulinum toxin do

cleaves presynaptic proteins involved in vesicle (acetylcholine) formation and blocks vesicle docking with the presynaptic membrane

12

what are the features of botulism

rapid onset weakness without sensory loss
overwhelming paralysis

13

what causes lambert eaton myasthenic syndrome (LEMS)

antibodies to presynaptic calcium channels leads to reduced vesicle release of ACh

14

what is LEMS strongly associated with

underlying small cell carcinoma
(50% paraneoplastic syndrome, 50% autoimmune)

15

what is the treatment for LEMS

3-4 diaminopyridine

16

what is the treatment for botulism

self limiting condition
supportive- ventilation

17

what is the main post synaptic MNJ disorder

myasthenia gravis

18

what causes myasthenia gravis

autoimmune disorder- antibodies against acetyl choline receptors
= reduced number of functioning receptors leads to muscle weakness and fatiguability
=flattening of end plate folds

even with normal amounts of ACh, transmission becomes insufficient when receptors drop by 30%

19

where do you get weakness in MG

strange presentations
-around eyes (ptosis)
-paraveterbal muscles
-facial muscles (square smile, flat facial expression)
-resp muscles (resp arrest)

20

what do the antibodies do in MG

block the binding of ACh and also trigger inflammatory response that damages the folds of postsynaptic membranes

21

what organ is particular involved in MG

thymus- 75% have hyperplasia/ thymoma

22

who gets MG

females in 3rd decade
males in 6/7th decade

23

what are the clinical features of MG

weakness typically fluctuating - worse at end of day
most commonly extraocular weakness, facial and bulbar weakness
limb weakness is typically proximal

(hard to keep eyes open watching TV,get tired eating meals)

24

what is the acute treatment for MG

-acetylcholinesterase inhibitor - pyridostigmine (allows persistence of ACh in the synaptic cleft)
- IV immunoglobulin

thymectomy (controversial)

25

what is the long term treatment for MG

-acetylcholinesterase inhibitor - pyridostigmine (allows persistence of ACh in the synaptic cleft)
(immunomodulation)
-steroids (high doses of prednisolone)
then
-steroid sparing agents (azathioprine/ mycophenolate)

emergency treatment with plasma exchange or immunoglobulin

26

what drug should you always avoid in MG

gentamicin - can cause MG crisis

27

what is the prognosis for MG

3-4%
from resp failure and aspiration pneumonia/ immunosuppression in the elderly

28

what is the smallest contractile unit in skeletal muscle

muscle fibre - sarcomere

29

what is a sarcomere

from one z line to the next, is the basic functional unit of the muscle

30

what are the features of LEMS

gradual onset of leg and arm weakness