Muscles Flashcards
What is a sarcolemma
Muscle cell membrane
What is a sarcoplasm
Muscle cell cytoplasm
What is a sarcoplasmic reticulum
Muscle cell endoplasmic reticulum
What is a sarcomere
Contractile muscle unit formed by myofibrils
Function of sarcoplasmic reticulum
Channel calcium into the muscle fibres
Neuromuscular transmission - muscle contraction
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
Which muscle fibres are aerobic
Type 1
Which muscle fibres are anaerobic
Type 2 a and type 2 x
What are type 1 muscle fibres
Slow contraction
High fatigue resistance
Aerobic
High mitochondrial and capillary density
High oxygen capacity
Fuelled by triglycerides
What are type 2 a muscle fibres
Moderately fast contraction
Long anaerobic activity
Medium power
High mitochondrial density
Intermediate capillary density
High oxidative capacity
Fueled by creatine phosphate and glycogen
What are type 2 x muscle fibres
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
What mechanisms counteract oxidative stress
Vit E - sarcolemma repair
Cysteine - respiratory chain and ROS
Q10 - reactive species - tca, amino-acid, fatty acids oxidation
What does inappropriate muscle strain lead to
Sarcolemma instability which releases markers into to bloodstream eg CK, AST, troponin
What type of damage does CK indicate
Sarcoplasm and mitochondrial
Rises quickly after damage
What does AST suggest
Whether muscle damage has stopped or is continuing
Clinical presentations of muscle damage
Stiffness, muscle pain, shortened stride, reluctance to move
Tachycardia, tachypnoea, recumbency, myoglobinuria, weakness
Paresis of specific muscles, arrhythmias, muscle atrophy
Diagnostic tests for CKv
Blood sample
Exercise
Wait 6 hours
Sample
If sample 2 is greater than or equal to 2x sample 1
How does pigmenturia occur
Cell rupture leads to myoglobin into circulation is filtered by kidney leads to pigmenturia
Contraindications for muscle biopsy
Evident diagnosis eg atypical myopathy
Condition successfully managed with husbandry - equine rhabdomyolysis
Indications for muscle biopsy
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
Which muscle is biopsied
Semi-membraneous
What sort of section of muscle should be removed
3x1cm following muscle fibres direction
What is periodic acid Schiff stain used for
Removing normal glycogen for PSSM testing
What is hande stain suggestive of
RER
Muscle cell nuclei move towards the centre of the cell as should be peripheral
What is desmin stain used for
Myofibrillar myopathy
Shows abnormal desmin distribution
How can you test for PSSM1
Validated genetic testing available as there is a mutation in the GYS-1 gene
Widely available (blood and hair plucks)
How can you test for PSSM2
Many unvalidated tests
What testing is used for atypical myopathy
Hypoglycin-A and toxic metabolite methylenecyclopropylacetic acid (MCPA)
Principle metabolite causing AM
Submit whole/spun sample
What definitive muscle tests are available
Hypoglycin A - atypical myopathy
PSSM1 - genetic testing
What is sporadic exertional rhabdomyolysis/causes
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
Clinical signs of exertional rhabdomyolysis
Stiff stilted hair
Excessive sweating
Increased respiratory rate
Reluctance to move
Dark urine
Risk factors for exertional rhabdomyolysis
Fit nervous horse
Young mares
No turnout
Held back during gallop
Rise in epinephrine
High resting cortisol
Trigger for exertional rhabdomyolysis
SERCA receptor dysfunction
Receptor in endoplasmic reticulum that allows removal of calcium and muscle relaxation
What breed is most prevalent for PSSM1
Continental European draft horses
Clinical signs of PSSM1
Stiffness after short exercise - reluctance to move forward, poor performance, sweating, more severe is myoglobinuria
What is PSSM
Polysaccharide storage myopathy
Abnormal glycogen storage - branches are not recognized by enzyme to be broken down so has excess inaccessible glycogen
What is PSSM2
Muscle disease with abnormal glycogen accumulation
Poor performance and elevation of muscle enzymes
