Lecture 14 - Muscles (2) (Part 2)

Question 1

What is Duchene’s muscular dystrophy?

What are the symptoms?

Answer 1

• X-linked recessive disorder that leads to a mutation in the dystrophin gene.
• Absence of dystrophin leads to excess Ca2+ entering muscle cell, which enters mitochondria and takes water with it, leading to rhabdomyolysis.
• Muscle cells are replaced by fat cells, which leads to
• Poor muscle tone, arched back, shoulders and arms fold back, poor balance, belly sticking out etc.

Question 2

What is the role of creatine kinase?
What can it be used to diagnose?
When is it released into the blood?

Answer 2

• To PP creatine facilitating storage of energy in the form of phosphocreatine.
• Can be used to diagnose myocardial infarction although largely superseded by troponin I assay.
• Released into blood by damaged skeletal muscle and brain - due to vaccinations, vigorous physical exercise, a fall, rhabdomyolysis, muscular dystrophy

Question 3

What are the 2 main markers of myocardial cell damage used clinically?

Answer 3

Troponin I &T assays, need to be measured within 20 hours.

Question 4

What is botulin toxin?

What does it cause and how?

Answer 4

• Toxin produced by botulinum clostridium
• Cleaves snare proteins and blocks NT release at motor end plate leading to flaccid paralysis (non-contractile state)
• Used to treat muscle spasms or cosmetically for wrinkles.

Question 5

How does organophosphate poisoning occur?

What are the effects of it?

Answer 5

• Inhibits ACh esterase, therefore ACh activity at NM junction is potentiated.
• Has effects on somatic and autonomic signalling.
• Acronym is SLUDGE for muscarinic effects and MTWTF for nicotinic.

Question 6

What is malignant hyperthermia?

Answer 6

• Severe reaction to anaesthetic succinylcholine due to RyR1 gene mutation, leads to increase Ca2+ release. Outcome is excessive heat, muscle contraction, acidosis etc. See muscle breakdown and hyperkalaemia.
• 75% mortality untreated, 5% if treated.