Muscles

Question 1

What is a sarcolemma

Answer 1

Muscle cell membrane

Question 2

What is a sarcoplasm

Answer 2

Muscle cell cytoplasm

Question 3

What is a sarcoplasmic reticulum

Answer 3

Muscle cell endoplasmic reticulum

Question 4

What is a sarcomere

Answer 4

Contractile muscle unit formed by myofibrils

Question 5

Function of sarcoplasmic reticulum

Answer 5

Channel calcium into the muscle fibres

Question 6

Neuromuscular transmission - muscle contraction

Answer 6

Neural signal down axon activated Ca entry into terminal axon
Ca interacts with snare proteins outside vesicles at terminal axon leads to acetylcholine release
Entry of Na on myofiber - depolarization current reaches sarcoplasmic reticulum through connecting tubules - Ca release within sarcoplasm
Ca binds troponin - tropomyosin unleashes acting and contraction begins

Question 7

Which muscle fibres are aerobic

Answer 7

Type 1

Question 8

Which muscle fibres are anaerobic

Answer 8

Type 2 a and type 2 x

Question 9

What are type 1 muscle fibres

Answer 9

Slow contraction
High fatigue resistance
Aerobic
High mitochondrial and capillary density
High oxygen capacity
Fuelled by triglycerides

Question 10

What are type 2 a muscle fibres

Answer 10

Moderately fast contraction
Long anaerobic activity
Medium power
High mitochondrial density
Intermediate capillary density
High oxidative capacity
Fueled by creatine phosphate and glycogen

Question 11

What are type 2 x muscle fibres

Answer 11

Fast contraction
Short term anaerobic muscles < 5 mins activity
High power
Medium mitochondrial and low capillary density
Moderate oxygen capacity
Fuelled by atp, creatinine phosphate and some glycogen

Question 12

What mechanisms counteract oxidative stress

Answer 12

Vit E - sarcolemma repair
Cysteine - respiratory chain and ROS
Q10 - reactive species - tca, amino-acid, fatty acids oxidation

Question 13

What does inappropriate muscle strain lead to

Answer 13

Sarcolemma instability which releases markers into to bloodstream eg CK, AST, troponin

Question 14

What type of damage does CK indicate

Answer 14

Sarcoplasm and mitochondrial
Rises quickly after damage

Question 15

What does AST suggest

Answer 15

Whether muscle damage has stopped or is continuing

Question 16

Clinical presentations of muscle damage

Answer 16

Stiffness, muscle pain, shortened stride, reluctance to move
Tachycardia, tachypnoea, recumbency, myoglobinuria, weakness
Paresis of specific muscles, arrhythmias, muscle atrophy

Question 17

Diagnostic tests for CKv

Answer 17

Blood sample
Exercise
Wait 6 hours
Sample
If sample 2 is greater than or equal to 2x sample 1

Question 18

How does pigmenturia occur

Answer 18

Cell rupture leads to myoglobin into circulation is filtered by kidney leads to pigmenturia

Question 19

Contraindications for muscle biopsy

Answer 19

Evident diagnosis eg atypical myopathy
Condition successfully managed with husbandry - equine rhabdomyolysis

Question 20

Indications for muscle biopsy

Answer 20

Repeated bouts of clinical disease that can’t be managed
Doubling baseline CK
Suspicion of storage myopathy
Need of definitive diagnosis
Poor performance with suspicion of muscle disease

Question 21

Which muscle is biopsied

Answer 21

Semi-membraneous

Question 22

What sort of section of muscle should be removed

Answer 22

3x1cm following muscle fibres direction

Question 23

What is periodic acid Schiff stain used for

Answer 23

Removing normal glycogen for PSSM testing

Question 24

What is hande stain suggestive of

Answer 24

RER
Muscle cell nuclei move towards the centre of the cell as should be peripheral

Question 25

What is desmin stain used for

Answer 25

Myofibrillar myopathy
Shows abnormal desmin distribution

Question 26

How can you test for PSSM1

Answer 26

Validated genetic testing available as there is a mutation in the GYS-1 gene
Widely available (blood and hair plucks)

Question 27

How can you test for PSSM2

Answer 27

Many unvalidated tests

Question 28

What testing is used for atypical myopathy

Answer 28

Hypoglycin-A and toxic metabolite methylenecyclopropylacetic acid (MCPA)
Principle metabolite causing AM
Submit whole/spun sample

Question 29

What definitive muscle tests are available

Answer 29

Hypoglycin A - atypical myopathy
PSSM1 - genetic testing

Question 30

What is sporadic exertional rhabdomyolysis/causes

Answer 30

Increase in work intensity without strong musculoskeletal foundation - z disk instability, over stretching of myofiber and sarcolemma stretching
Dietary imbalances eg electrolyte imbalance and low vit E meaning poor antioxidant state
Exhaustion - electrolyte loss specifically in humid weather

Question 31

Clinical signs of exertional rhabdomyolysis

Answer 31

Stiff stilted hair
Excessive sweating
Increased respiratory rate
Reluctance to move
Dark urine

Question 32

Risk factors for exertional rhabdomyolysis

Answer 32

Fit nervous horse
Young mares
No turnout
Held back during gallop
Rise in epinephrine
High resting cortisol

Question 33

Trigger for exertional rhabdomyolysis

Answer 33

SERCA receptor dysfunction
Receptor in endoplasmic reticulum that allows removal of calcium and muscle relaxation

Question 34

What breed is most prevalent for PSSM1

Answer 34

Continental European draft horses

Question 35

Clinical signs of PSSM1

Answer 35

Stiffness after short exercise - reluctance to move forward, poor performance, sweating, more severe is myoglobinuria

Question 36

What is PSSM

Answer 36

Polysaccharide storage myopathy
Abnormal glycogen storage - branches are not recognized by enzyme to be broken down so has excess inaccessible glycogen

Question 37

What is PSSM2

Answer 37

Muscle disease with abnormal glycogen accumulation
Poor performance and elevation of muscle enzymes