L15 Muscle Injury

Question 1

What are some of the causes of muscle injury?

Answer 1

Alcohol intake
Chemical and drugs
Diseases - like polymyositis. Muscular dystrophy, biochemical disorders
Irradiation
Ischaemia 
Mechanical injuries - stretch, crushing, cutting
Thermal injuries
Biological toxins 
Exercise - especially eccentric
Low frequency fatigue

Question 2

What can be used as a damage marker (in different isoforms) for muscular injuries and why?

Answer 2

Plasma creatine kinase.

it usually onsets after DOMs and after the exercise. A regenerating muscle will show the muscle cells with their nuclei on the outside of the cell. which can be shown under a microscope.

Question 3

What does low frequency fatigue do to the force-calcium curve?

Answer 3

shifts it to the right.

Less force for the same amount of calcium released.

Question 4

What happens at the muscle what a Plasmalemma tear occurs

Answer 4

1. calcium enters
2. This activates proteases which will break down proteins in myofibrils, mitochondria and cytoskeleton.
3. This can spread and cause death of the fibre.
   OR
4. T-cells arrive due to cytokine liberation. Macrophages remove debris as satellite cells are activated –> myoblasts form a myotube around the tear to form a stump with a new membrane
5. repair complete

Question 5

How is pain sensed?

Answer 5

activation of thin fibre afferents.

Group III an IV afferents, latter aka c-fibres

Question 6

What causes the afferents that sense pain to become active?

Answer 6

Metabolites, raised temperature and muscle force

Question 7

What causes DOMs?

Answer 7

• Metabolites like bradykinin, glutamate and ATP
• Nerve growth factor (NGF) is produced in inflamed tissue after ischaemia - it sensitises nociceptors and causes lasting tenderness