NMJ and Muscle disorders Flashcards Preview

Neurology > NMJ and Muscle disorders > Flashcards

Flashcards in NMJ and Muscle disorders Deck (59):
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

31

what surrounds each muscle fibre

endomysium

32

what forms a fascicle

20-80 muscle fibres

33

what wraps round a fascile

perimysium

34

what wraps around skeletal msucle

epimysium (extends from tendon)

35

what are the features of smooth muscles

not striated
single central nucleus
gap junction between cells
no sarcomeres

36

what are the different types of muscle fibres

type 1- slow oxidative (dense capillary network, myoglobin, resist fatigue)
type IIa - fast oxidative (aerobic metabolism)
type IIb- fast glycolytic (easily fatigued)

37

what are fasciculations

visible fast, fine, spontaneous twitch

38

can fasciculations be normal

yes in healthy muscles (large) can be caused by stress, caffeine, fatigue

39

when are fasciulations abnormal

occur in denervated muscle which becomes hyperexcitable - usually a sign of disease in the motor neurone not the muscle
(abnormal in small muscles)

40

what is myotonia

failure of muscle relaxation after use
due to chloride channel disorder (usually hereditary)

41

what are the symptoms/ signs of muscle disease

myalgia
muscle weakness
wasting
hyporeflexia

42

what are the causes of neck weakness with drop

motor disease
muscle disorders
myositis
myopathy

43

what are the immune mediated muscle diseases

dermatomyositis
polymyositis

44

what are the inherited muscle diseases

muscular dystrophies
dystrophinopathies
limb girls muscular dystrophies
myogenic dystrophy

45

what are the congenital muscles diseases

congential myasthenic syndromes
congenital myopathies

46

what are the symptoms/ signs of polymyositis

symmetrical, progressive proximal weakness developing over weeks to months
Raised CK (in 1000s)- responds to steroid

47

what are the symptoms/ signs of dermatimyositis

clinically similar but associated with skin lesions 'heliotrope rash'
50% have underlying malignancy

48

what is inclusion body myositis

slowly progressive weakness in 6th decade of life with characteristic thumb sparing

49

what is myotonic dystrophy

commonest muscular dystrophy
AD

50

what are the features of myotonic dystrophy

myotonia
weakness
cataracts
ptosis
frontal balding
cardiac defects

51

what are the features of muscular dystrophies

inherited
noninflammatory
progressive
no central/ peripheral nerve abnormality

duchenne and becker most common

52

what are the common infective muscle diseases

viral- coxsacchie
trypanosomiasis
cistercosis - uncooked pork
borrelia

53

what are the toxic causes of muscle disease

drugs
venoms

54

what are the congenital muscle diseases

congenital myasthenic syndromes
congenital myopathies

55

what drugs cause myopathies

statins- myalgia, myopathy, persistent myositis
steroids
duiretics

56

what is rhabdomyolosis

dissolution of muscle
damage to skeletal muscle causes leakage of large quantities of toxic intracellular contents into plasma

57

what can cause rhabdomyolsis

crush injuries
toxins
post convulsions
extreme exercise

58

what are the features of rhabdomyolsis

myalgia
muscle weakness
myoglobinuria
complications = acute renal failure and DIC

59

what are the MRC muscle power grades

0 – no movement at all
1 - flicker of movement when attempting to contract muscle
2 – some muscle movement if gravity removed but none against gravity
3 - movement against gravity but not against resistance
4 – movement against resistance but not full strength
4- not alright but they are managing
4+ almost normal but not quite
5 – normal strength