Disorders of the Motor Unit Flashcards
2 classifications of motoneurones
- Upper motoneurones
- Lower motoneurones
What does damage to each of the classification of motoneurones lead to?
- U = upper motoneurone signs
- L = lower motoneurones signs
What does death or dysfunction of muscle lead to?
Motor signs similar to lower motoneurone signs
What type of motoneurone innervates skeletal muscle?
α-motoneurones
What is polio myelitis?
A communicable infection that targets the cell bodies of lower motoneurones
What happens in polio myelitis and what does it lead to?
Infection by polio virus means toxic infection (death) of cell bodies of neurones of the ventral horn, leading to denervation and hence paralysis of muscle that was supplied
2 variants of motoneurone disease
- Disease kills upper and lower motoneurones simultaneously
- Disease targets only lower motoneurones
What motoneurones do not undergo apoptosis under motoneurone disease?
- Motoneurones supplying extraocular muscles
- Motoneurones supplying the anal sphincter (S2-4)
How does botulinum toxin affect the NMJ and what does this lead to?
Depletes the the presynaptic terminal of its neurotransmitter leading to paralysis of muscles
What do nerve gases contain that makes them dangerous?
Organophosphates
How do organophosphates affect the NMJ and what does it lead to?
Block acetylcholinesterase from breaking down Ach leading to overstimulation of muscle
What happens when a person has myasthenia gravis?
Their immune system selectively destroys nicotinic receptors on the post-synaptic membrane of the NMJ, leading to flaccid weakness of affected muscles
What is Duchenne muscular dystrophy?
Genetic disorder causing defects in muscle proteins and then muscle tissue death, eventually causing death of the individual
Types of lower motoneurone sign
- Flaccid muscle weakness
- Hypotonia or atonia (absent or weak muscle tone)
- Hyporeflexia or areflexia (absent or weak muscle tone)
- Denervation of muscle atrophy
- Fasciculations (worms in a bag)
- Muscle wasting
