exam 1 lecture 5 muscle metabolism Flashcards
The equilibrium potential for A+ is +50 mV, the concentration inside of the cell is 10 mM, and the concentration outside of the cell is 100 mM.
The equilibrium potential for B+ is -100 mV, the concentration inside of the cell is 130 mM, and the concentration outside of the cell is 7 mM.
The resting membrane potential for the cell is -70 mV
Q: The cell is at rest and then a ligand gated A+ channel opens. Which way will the A+ ions move?
into the cell
HYPP impressive syndrome
mutation in Na channel.
Na allowed to enter cell, causing depolarization and action potential of the muscle- leads to trembling, weakness and collapse
triggered by stress and made worse by hyperkalemia (too much potassium)
how does hyperkalemia make HYPP worse?
too much potassium outside of cell
gradient between inside and outside less, potassium will not want to move out of cell as quickly, action potential will be slower to repolarize
what is rigor mortis?
no ATP available so cross bridges cant let go of the actin, muscle stays contracted
Myasthenia Gravis is in an autoimmune disease that attacks nAChRs in the NMJ of skeletal muscle.
What symptoms might you expect to see?
What do you think could be some potential mechanisms/targets for a treatment?
nicotinic cholingeric receptor → binds to ACh and lets K and Na into and out of cell
if this doesn’t work action potential does not start in muscle= no contraction
increase amount of ACh, decrease the amount of acetylcholinesterase
how to test for myathenia gravis
myathenia gravis is when nicotinic cholinergic receptors don’t work correctly
Tensilon (edrophonium chloride) – an acetylcholinesterase inhibitor which blocks acetylcholine breakdown in the NMJ
- Accumulated ACh prolongs muscle stimulation and so increases muscle strength temporarily
- Oral form (pyridostigmine) is used for long term treatment.
___ is the mechanical response resulting from a single action potential
muscle twitch
the speed of a muscle twitch differs depending on muscle fiber type and ___
load
How do Ca2+ levels change during the different phases of a twitch?
latent period: action potential moving across sarcolemma and down T tubules, getting ready to release Calcium
contraction: calcium released
relaxation: calcium taken back up into the SR
___ the muscle length is unchanged during contraction
isometric (carrying beer)
___ is when the muscle changes length under a constant load during contraction
isotonic
can be concentric or eccentric
___ is when the muscle shortens during contraction
concentric
type of isotonic contraction
(bicep curl, bring beer to your face)
___ is when muscle lengthens during contraction
eccentric
type of isotonic contraction
lowering beer to the ground
why no plateau?
muscle not strong enough the lift 20 g thing, can not contract, will stay the same size (isometric contraction)
The force generated in muscle fibers depends on the number of exposed myosin binding sites on actin and the number of active ___
crossbridges
How do you think a muscle cell can increase the number of crossbridges?
increase the speed at which calcium is taken up into the SR so that the calcium is then ready to be used again to bind to troponin, move tropomyosin and allow myosin to bind to actin
explain how frequency of stimulation from a twitch generates force
the twitch will build on to each other until all fibers are filled (tetanus)
additive effect of increased stimulation rate
larger diameter fibers have more ___ which leads to more cross bridges and more force-generating capacity
myofibrils
Hypertrophy
increasing the diameter of the muscle cell by increasing the number of myofibrils
hyperplasia
increasing the number of muscle cells. Not Common
length-tension relationship
•Sarcomere length (pre-stimulus) affects the possible number of cross bridges
if too stretched or squished cant reach 100% of its strength
how can we increase the distance a muscle can shorten
increase the number of sarcomeres
•As we increase the length of the fiber by adding sarcomeres, a given stretch or shortening from the rest length will be distributed over a greater number of sarcomeres.
makes each sarcomere work less for the same amount of distance- smaller change in the length of each sarcomere
what does this show
longer fibers have more sarcomere so they have a larger range at which they can work at 100% because the work is divided into a bunch of sarcomeres
a shorter fiber would have to work much harder to get the same distance
Is There A Disadvantage To Having Long Fibers?
Yes: Increasing the number of sarcomeres in series does not increase the maximum tension, but it does increase the amount of energy required.
Magnitude of the load: The load on the muscle influences the ___of the crossbridge cycle
kinetics
heavier load= takes longer to shorten
longer muscle fibers have ___ shortening ranges and ___ shortening rates
larger
faster
Can contract more because it has more sarcomeres, faster at contracting then smaller muscle fibers
how does creatine phosphate act as an energy source for contraction?
creatine phosphate → creatine + ATP
ATP is released during the dephosphorylation of creatine phosphate into creatine
reversible reaction dependent of creatine kinase (happens in the intermembrane space of the mitochondria)
muscle cells store glycogen which can be broken down into __
glucose-6-phosphate → pyruvate
skeletal muscle lacks glucose-6-phosphatase can’t move glucose-6-phosphate → glucose
skeletal muscle lacks glucose-6-phosphatase. What does this mean
can’t move glucose-6-phosphate → glucose
glycogen in skeletal muscle does not contribute to blood sugar, needs the glucose for itself.
