Neuromuscular junction disorders

Question 1

What are skeletal muscle fibres innervated by?

Answer 1

Motor neurones

Question 2

What is the neuromuscular junction?

Answer 2

The connection between a motor neurone and muscle fibre

Question 3

What is the function of the NM junction?

Answer 3

This is where the motor neurone stimulates the muscle fibre to eventually lead to muscle contraction

Question 4

What is present on the terminal end of the motor neurone?

Answer 4

ACh vesicle

Question 5

Muscle fibres contain which type of receptors?

Answer 5

ACh

Question 6

The arrival of AP to the NMJ causes what to happen?

Answer 6

Voltage activated Calcium channels open allowing influx of calcium.
Also, ACh vesicles from the motor neurone are released into the synaptic cleft.
ACh receptors on the muscle open and this renders the membrane permeable to Na+ / K+ ions

Question 7

Why is breakdown of ACh important?

Answer 7

Persistence of ACh leads to cholinergic crisis and paralysis

Question 8

Name 2 pre-synaptic disorders of the NMJ?

Answer 8

Botulism

Lambert Eaton Myasthenic Syndrome

Question 9

Botulism - definition

Answer 9

Botox cleaves the pre-synaptic proteins involved in vesicle formation and blocks vesicle from docking with the pre-synaptic membrane

Question 10

Botulism - clinical features

Answer 10

Weakness
Blurred vision
Flaccid paralysis
NO sensory loss

Question 11

LEMS - there is a strong association with which condition?

Answer 11

SCLC

Question 12

LEMS - clinical features

Answer 12

Upper limb weakness

Decreased tone reflexes

Question 13

LEMS - management

Answer 13

3-4 diaminopyridine

Question 14

Name a post-synaptic NMJ disorder

Answer 14

Myasthenia gravis

Question 15

Myasthenia gravis - definition

Answer 15

Reduced number of functioning ACh receptors leads to muscle weakness and fatiguability

Question 16

Myasthenia gravis is an auto-immune condition. True or false?

Answer 16

True

- Formation of antibodies to ACh receptors which block binding of ACh

Question 17

Myasthenia gravis - antibodies have an affect on the endplate folds of the post synaptic membrane. True or false?

Answer 17

True

Question 18

Myasthenia gravis - more common in young MEN/WOMEN and more common in old MEN/WOMEN

Answer 18

young women

old men

Question 19

Myasthenia gravis - what is the patients main complaint

Answer 19

Generalised weakness

Question 20

Myasthenia gravis - clinical features

Answer 20

Generalised weakness 
Fatigue 
Bilateral facial weakness
Extraocular weakness - ptosis 
Diplopia 
Bulbar weakness 
Limb weakness

Question 21

Myasthenia gravis - limb weakness is usually proximal/distal?

Answer 21

Proximal

Question 22

Myasthenia gravis - examination

Answer 22

Get the patient to blink 20 times (this exercises the muscle and towards the end of this exercise, the patient will be very weak)

Question 23

Myasthenia gravis - how is the diagnosis made

Answer 23

Presence of ACh receptor antibodies

Question 24

Myasthenia gravis - acute management

Answer 24

Acetylcholinesterase inhibitor (PYRIDOSTIGMINE) 
- now the ACh cannot be b/d so it is more likely to bind to the ACh receptor 

IV immunoglobulin
Plasma exchange

Question 25

Myasthenia gravis - chronic management

Answer 25

Steroids

Steroid sparing agents

Question 26

Myasthenia gravis - which drug should be avoided as it makes the patient weaker

Answer 26

Gentamicin

Question 27

Rhabdomyolysis - definition

Answer 27

Damage to skeletal muscle causes leakage of large quantities of toxic intracellular contents into the plasma

Question 28

Rhabdomyolysis - causes

Answer 28

Crush injuries
Toxins
Post convulsions
Extreme exercise

Question 29

Rhabdomyolysis - clinical features

Answer 29

Myalgia

Muscle weakness