Neuromuscular Flashcards
What is the volume of blood flow to skeletal muscle in a racehorse exercising at VO2max in terms of rate and percentage of cardiac output?
A. 226 L/min; 69%.
B. 192 L/min; 68%.
C. 226 L/min; 78%.
D. 195 L/min; 78%.
C. 226 L/min; 78%.
Ref: Equine Exercise Physiology, Hinchcliff, Geor and Kaneps, Elsevier Ltd 2008.
Skeletal muscle consists of myofibres, blood vessels, nerves, fat and connective tissue. What percentage of skeletal muscle consists of myofibres?
A. 75%.
B. 90%.
C. 83%.
D. 97%.
B. 90%.
Ref: Equine Exercise Physiology, Hinchcliff, Geor and Kaneps, Elsevier Ltd 2008.
Identify the component of the contractile apparatus marked by an asterix in the diagram below:
A. M line.
B. I band.
C. Z disk.
D. A band.
A. M line.
Ref: Equine Exercise Physiology, Hinchcliff, Geor and Kaneps, Elsevier Ltd 2008.
Calcium is essential for skeletal muscle contraction. Which of the following statements is true regarding movement of calcium within skeletal muscle fibres?
A. Action potentials are conducted into the interior of muscle fibres via the T-tubules and there activate dihydropyridine receptors (DHPR). Activation of DHPR promotes movement of calcium ions into the cell from the extracellular space.
B. Action potentials are conducted into the interior of muscle fibres via the T-tubules and there activate the ryanodine receptor (RYR1), which promotes influx of calcium ions into the cell from the extracellular space.
C. Interaction between DHPR and RYR1 causes release of calsequestrin-bound Ca2+ from the sarcoplasmic reticulum. This continues in a positive feedback loop, where calcium promotes further activation of RYR1, and the calcium concentration within the cytoplasm increases about 100-fold from its resting concentration.
D. Free calcium ions within the cytoplasm of myofibrils bind with high affinity binding sites on troponin I to cause a conformational change in the troponin-tropomyosin complex and subsequent shortening of the sarcomere.
C. Interaction between DHPR and RYR1 causes release of calsequestrin-bound Ca2+ from the sarcoplasmic reticulum. This continues in a positive feedback loop, where calcium promotes further activation of RYR1, and the calcium concentration within the cytoplasm increases about 100-fold from its resting concentration.
Unlike in cardiac muscle, there is little influx of calcium into the cell following propagation of an action potential, instead the calcium ions enter the cytoplasm following release from the sarcoplasmic reticulum. They then bind to tropon C and muscle contraction results.
Ref: Equine Exercise Physiology, Hinchcliff, Geor and Kaneps, Elsevier Ltd 2008.
Muscle fibre composition has an important influence on performance. Which of the following muscle fibre characteristics are ideal for endurance exercise?
A. High number of type II fibres and high capacity for anaerobic glycolysis.
B. High number of type II fibres.
C. High number of type I and IIX fibres and high oxidative capacity.
D. High number of type I and IIA fibres and high activity of oxidative enzymes.
D. High number of type I and IIA fibres and high activity of oxidative enzymes.
High number of type II fibres are advantageous in sprinters.
Stride length and frequency are positively correlated with both the percentage of IIA fibres and fibre size, and the stance time of the stride is inversely correlated with the percentage of IIX fibre and fibre diameter.
Ref: Equine Exercise Physiology, Hinchcliff, Geor and Kaneps, Elsevier Ltd 2008.
The above horse has an autosomal dominant inherited disorder causing a mutation in his α sodium channel subunits. He has had clinical episodes of this disorder in the past following intense exercise and his owners asks you what she can do to try and prevent episodes again in the future. What medication do you recommend for this purpose and what is its mode of action?
A. Phenytoin; voltage-dependent block of voltage gated sodium channels.
B. Dantrolene sodium; bind to RYR1 and prevents release of calcium from sarcoplasmic reticulum.
C. α-tocopherol; anti-oxidant.
D. Acetazolamide; carbonic anhydrase inhibitor.
D. Acetazolamide; carbonic anhydrase inhibitor.
The horse has HYPP. Acetazolamide can be given prior to general anaesthesia or other known stressors to decrease the risk of a clinical HYPP episode occurring. Mild exercise or oral administration of corn syrup have been reported to abort mild episodes. Treatment during an episode includes administration of sodium bicarbonate, glucose, insulin (all drive potassium into the cells), IV fluids, anti-inflammatories.
The image above shows histological slides from semimembranosus muscle biopsies from two horses diagnosed with polysaccharide storage myopathy stained with periodic acid Schiff’s stain. Based on the characteristics of the myofibres in these images, which horse is more likely to be a Percheron?
A. A
B. B.
C. Neither came from a Percheron.
D. Either sample is equally likely to have come from a Percheron.
A. A
Sample 1 came from a horse with type 1 PSSM - abnormal polysaccharide is coarse granular and is more commonly cytoplasmic. Sample 2 came from a horse with type 2 PSSM - abnormal polysaccharide is fine granular or homogenous and more commonly located in the sarcolemma.
Type 1 PSSM occurs most commonly in warmbloods and draft horses with continental European bloodlines Percherons (62% of 149 horses sampled in one study were positive for the PSSM1 mutation) and Belgian warmbloods (39%). Reported in approx 20 breeds but prevalence is lower e.g. 6.6% QH (22/335).
You diagnose a 7 year old Morgan mare used for low level dressage with type 2 PSSM. She is a body condition score of 7/9, weighs 467kg, has good muscle tone and is worked 4-5 times a week from 6.30-7.30am before her owner goes to work. Which of the following diets would be most appropriate for this horse?
A. Free choice grazing plus 1kg performance horse pellets fed once a day.
B. 7kg of 10% NSC hay, split into 2 meals fed at 5.30am and 5.30pm plus 2kg of a <10% NSC, 20% fat commercial pelleted feed fed once a day.
C. 7kg of 10% NSC hay, split into 3 meals fed at 8am, 2pm and 10pm plus an electrolyte and mineral ration balancer.
D. 1 hour grazing at dusk, 6kg 14% NSC hay split into 2 meals fed at 5.30am and 5.30pm plus 1kg of a <10% NSC, 20% fat commercial pelleted feed fed once a day.
C. 7kg of 10% NSC hay, split into 3 meals fed at 8am, 2pm and 10pm plus an electrolyte and mineral ration balancer.
This horse is overweight! She should be fed at 1.5% BWt forage per day (7kg) with hay that is £12% NSC plus a ration balancer. This horse is only performing low level exercise so doesn’t need additional concentrates. For horses with PSSM in heavier work/lower BCS feeding a low starch/high fat grain or a fat supplement is important as they then have less glucose uptake into muscle cells and provision of more plasma free fatty acids for use in muscle fibres during aerobic exercise. In overweight horses it is not advisable to supplement them with fat, however fasting them for 6 hours before exercise can increase the amount of circulating free fatty acids.
NB NSC are lowest in pasture first thing in the morning not at dusk!
Ref: S. Valberg Michican State Equine Neuromuscular Lab PSSM notes; https://cvm.msu.edu/research/faculty-research/valberg-laboratory/type-1-polysaccharide-storage-myopathy#13.-how-do-i-prevent-another-episode-of-tying-up-in-my-pssm-1-horse?
You diagnose a horse with Equine Motor Neuron Disease on the basis of classic muscle histology findings. Which other abnormalities in locations outside the musculoskeletal system have been reported in multiple horses with EMND?
A. Granulomatous enteritis and facial nerve paralysis.
B. Pigment retinopathy and eosinophilic enteritis.
C. Uveal cysts and hepatic lipoid deposition.
D. Renal tubular nephrosis and coronary band separation.
B. Pigment retinopathy and eosinophilic enteritis.
Ref: de Castro, J Vet Intern Med 2016; 30:873–879; Finno et al, Vet Ophthalmol, 2016; Riis et al, Equine Vet J, 1999; 31:99-110.
Which of the following thoroughbred horses in race training is most likely to suffer from recurrent exertional rhabdomyolysis?
A. 3 year old filly fed 5kg oat-barley mix once a day and free choice Lucerne hay.
B. 4 year old filly fed 5kg oat-barley mix once a day and free choice Lucerne hay.
C. 2 year old colt fed 3kg 12% protein, 7% fat pelleted feed once a day and free choice grazing.
D. 4 year old colt fed 3kg 12% protein, 7% fat pelleted feed once a day and free choice grazing.
A. 3 year old filly fed 5kg oat-barley mix once a day and free choice Lucerne hay.
Risk factors for RER:
Age effect: Two-year-olds tie-up more frequently than three-year-olds, which in turn tie-up more frequently than four-year-old or older horses.
Gender effect: 65% were fillies
Temperament effect: 48% of tie-up horses were characterized as nervous, versus 24% of the controls
Lameness effect: Lameness was more common in tie-up horses
Diet effect: Most horses that tied up were fed >10lbs of grain/sweet feed/day
Exercise intensity effect: Racehorses tied-up most often with gallop training, and not when breezing or racing.
Ref: S. Valberg Michican State Equine Neuromuscular Lab RER notes; https://cvm.msu.edu/research/faculty-research/valberg-laboratory/recurrent-exertional-rhabdomyolysis
The above horse presents to you for evaluation of progressive weight loss, muscle atrophy and weakness. You submit samples for serum muscle enzyme, serum vitamin E and muscle vitamin E concentration measurement and a muscle biopsy sample from the sacrocaudalis dorsalis muscle for histology with special staining. Her serum vitamin E and creatinine kinase concentrations are within the reference range, her serum aspartate transaminase concentrate was 380 U/L (160-300 U/L) and her muscle vitamin E concentration was 0.5ug/g (3.6-8.1 ug/g). Histology revealed redistribution of mitochondrial enzyme stain (moth-eaten appearance) with the NADH-Tr stain and an absence of neurogenic angular atrophy of myofibres. What diagnosis do you make?
A. Vitamin E deficient-myopathy.
B. Equine motor neuron disease.
C. Equine degenerative myeloencephalopathy.
D. Nutritional myodegeneration.
A. Vitamin E deficient myopathy.
A vitamin E–deficient myopathy characterized histologically by a moth-eaten appearance in the mitochondria and anguloid myofiber atrophy in frozen sections of sacrocaudalis dorsalis medialis muscle biopsy specimens was found in horses with clinical signs of EMND that were highly responsive to vitamin E treatment. This myopathy may be a specific syndrome or possibly precede the development of neurogenic muscle fibre atrophy typical of EMND.
Ref: Bedford et al, J Am Vet Med Assoc, 2013; 242:1127–1137.
Based on the work by Wildberger et al, 2015, which of the following statements is most likely to be true regarding Arabian horses that develop exertional rhabdomyolysis (ER) following endurance exercise?
A. The prevalence of ER is higher following 100 mile rides than 50 mile rides.
B. GYS1 mutations occur in 50% of Arabian horses with ER.
C. The prevalence of ER is 14% in Arabian and Arabian cross horses completing 50 mile endurance rides in North America.
D. The cause of ER in endurance athletes is unknown, but it is unlikely to be malignant hyperthermia or type 1 PSSM.
D. The cause of ER in endurance athletes is unknown, but it is unlikely to be malignant hyperthermia or type 1 PSSM.
Incidence of ER in this sample of 101 horses completing a 50 mile ride was 4%. None of the affected horses were positive for GYS1 or RYR1 mutations in hair samples.
Ref: Wilberger et al, Equine Vet J, 2015; 47:165-170.
