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EQN*3050 Muscle Physiology
equine physiology muscle
62
Physiology
Undergraduate 3
01/22/2015

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Term
What are the 3 types of muscles
Definition
smooth
cardiac
skeletal
Term
Muscle mass comprises approx ___% of the horse's body weight
Definition
55%
Term
Describe the # of mitochondria in cardiac, skeletal and smooth muscle
Definition
Cardiac: high #
Skeletal: variable
Smooth: low #
Term
Which muscle types have high resistance to fatigue?
Definition
cardiac & smooth
Term
The muscle cell membrane is known as the...
Definition
sarcolemma
Term
What is a myofibril?
Definition
filament within a muscle cell
Term
What attaches muscle do bone
Definition
tendon
Term
What is the functional centre of myosin filaments?
Definition
M-line
Term
What is the region of overlap between the I-band & H-band?
Definition
A band
Term
What is found in the I-band? H-band?
Definition
I: actin filaments
H: myosin filaments
Term
As # of fibres innervated by a neuron increases, magnitude of force produced by the muscle _____
Definition
increases
Term
Which have a higher threshold, nerves with narrow diameter or wide?
Definition
wide diameter have higher threshold
Term
Do narrow nerve fibers or wide fibers offer a fine motor control?
Definition
narrow
Term
Where is calcium stored in muscle cells? What triggers its release? What does its release trigger
Definition
sarcoplasmic reticulum

-release triggered by AP in T-tubules

-release of Ca triggers contraction of sarocomeres
Term
Describe depolarization of a muscle nerve cell
Definition
1. AChR channels open, Na enters cell
2. Na entry triggers release of voltage-dep Na channels
3. T-system depolarizan triggers Ca2+ release from SR
4. Contraction initiated
Term
Are sodium channels energy or gradient dependent?
Definition
gradient
Term
For every __ sodium moving out through the Na:K pump, __ K move in
Definition
3 Na out
2 K in
Term
What is summation?
Definition
stimulation of a muscle nerve before repolarization has completed triggering a 2nd contraction with greater tension
Term
What is fused tetanus?
Definition
When a muscle enters a tetanic state (cramped) in a constant state of contraction
Term
What is the long protein wrapped around an actin filament
Definition
tropomyosin
Term
What is troponin? What does it do?
Definition
TrC, TrI & TrT proteins embedded within tropomyosin

-regulates binding of myosin heads to actin filaments
Term
How is Ca involved in the troponin/tropomyosin interaction?
Definition
Ca interacts with troponin, inducing conformational change in tropomyosin allowing myosin heads to bind to actin
Term
How is ATP involve in contraction?
Definition
-binds to myosin head
-hydrolysis will release ADP, energy allows myosin head to crawl along actin filament
-ATP binds to myosin again, causing it to detach from actin
Term
What checkpoints in the contraction/relaxation cycle require ATP?
Definition
myosin head conformational change
Na:K pump
Ca pump
Term
What is RER?
Definition
Recurrent Exertional Rhabdomyolysis
-tying up
-associated with intense exercise
-defect in intracellular Ca regulation
Term
What is PSSM?
Definition
Polysaccharide Storage Myopathy
-mutation in GYSI gene (glycogen synthase)
-can form & store glycogen but cannot access it, accumulates in skeletal muscle
-lower AP threshold stimulus
Term
What is HYPP?
Definition
Hyperkalemic Periodic Paralysis
-defect in Na channels
-leaky mmb allowing excess Na to enter cell
-increases K outside cell, reducing mmb potential triggering contraction
Term
True or False

Actin has ATPase activity
Definition
false
Term
Do fast fibers rely on anaerobic or aerobic pathways?
Definition
anaerobic
Term
Are Type I, Type IIB and Type IIA fast or slow twitch muscles? Low or high oxidative? Which of the fast-twitch are fatigue-resistant?
Definition
Type I: slow twitch, low oxidative
Type IIB: fast twitch, low oxidative
Type IIA: fast twitch, high oxidative, fatigue-resistant
Term
Which type of muscle fibers would be used for long, slow physical activity?
Definition
Type I
Term
Which has more muscle fibers per nerve, Type I or Type II?
Definition
Type I
Term
How many net ATP are produced during anaerobic ATP production?
Definition
2
Term
How long does it take for a horse to restore glycogen stores after exhaustive exercise?
Definition
72h
Term
When is phosphocreatine used for ATP production?
Definition
at onset of exercise and during sporadic periods of high intensity
Term
Why is anaerobic ATP production self-limiting?
Definition
-need NAD to feed G3P
-glycogen is depleted and takes 72h to restore
-lactic acid production lowers pH, inhibiting enzymes involved in glycolysis
Term
How many ATP are produced during aerobic production?
Definition
38
Term
What are the muscle substrates for aerobic ATP production?
Definition
glycogen
palmitic acid (fat)
Term
What do the following RER indicate:

0.7
1.0 > RER > 0.7
1
Definition
0.7: free fatty acids are being used
1.0 > RER > 0.7: CHO and FFA being used
1: CHO is being used, fully oxidized
Term
Why does it take longer to use fat as an energy source?
Definition
must first mobilize it & bring to the muscle
Term
True or False

PSSM horses are insensitive to insulin
Definition
False

highly sensitive

-triggers storage of CHO as glycogen but cannot use effectively
Term
What is the Bohr shift?
Definition
low pH and high CO2 during exericise stimulates 'downloading' of O2 from hemoglobin, replacing it with H+ or CO2 to moderate pH levels
Term
What percentage of energy released with ATP is hydrolyzed is used for mechanical work?
Definition
25%
Term
What causes muscle soreness during/after exercise?
Definition
H+, NOT LACTATE
Term
True or False

Lactate is essential for sprinting
Definition
true
Term
Why is lactate important?
Definition
converted to pyruvate using lactate dehydrogenase, producing NAD+

-lactate provides fuel for mitochondria
Term
How long does it take for physiological responses to be improved with training?
Definition
10 days to 16 weeks
Term
What is strain?
Definition
abnormal adaptations to excessive stress
Term
What is the role of cortisol during stress?
Definition
prepares the body for glycogen sparing
Term
Fatigue due to sub-maximal exercise is usually due to...
Definition
depletion of glycogen stores
hyperthermia
Term
Fatigue due to high intensity exercise is usually due to...
Definition
depletion of PCr & ATP
acidosis
Term
what effect does a K imbalance have on muscle function?
Definition
impairs perfusion of muscles with blood, reducing ability to remove metabolic waste/provide nutrients
Term
What effect does a Ca/Mg imbalance have on muscle function?
Definition
sensitives the phrenic nerve, causing the diaphragm to contract at the same rate as the heart
(the thumps)
Term
What effect do imbalances of Na/Cl/K/Mg have on muscle function?
Definition
impairs distribution of electrical charge across cell membranes
Term
What is milkshaking?
Definition
feeding sodium bicarbonate to increase pH of blood and muscle, facilitating lactate eflux and sparing the use of ATP (prolonging fatigue)
Term
What meets the glucose needs of an organism as a whole?
Definition
liver glycogen
Term
What meets the glucose needs of specific muscles?
Definition
the glycogen stored in the muscle in question
Term
How does glycogen provide energy?
Definition
broken down to G-6-P, used in glycolysis for ATP & NADPH production
Term
Why does it take so long to restore glycogen levels in a horse post-exercise?
Definition
exhaustive exercise does not trigger a spike in insulin, which is required to increase uptake of glucose from the blood to be stored as glycogen
Term
What effect does low muscle glycogen have on muscle contraction?
Definition
impaired the release of Ca2+ from the SR
-less response from T tubules to depolarization
Term
What effect does acetate have on restoring muscle glycogen?
Definition
increases storage levels 4h after exercise, but no net gain 24h post exercise
Term
What effect do electrolytes have on restoring muscle glycogen?
Definition
increases rate of post-exercise glycogen resynthesis
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