Excitation-Contraction Coupling Flashcards
What is the purpose of subneural clefts?
increase surface area on post-synaptic cleft so there are more receptors available
After repolarization, what happens to DHP and RyR?
DHP changes back to original shape first –> then RyR goes back too
What type of muscle would have more nerve fibers in it?
smaller, more precise muscles - allows it to have more control
Once the ACh has been released into synaptic cleft, what happens to the post-synaptic membrane (nicatinic receptor)?
ACh goes to nAChR –> allows Na into cell –> more + in cell–> triggers voltage-activated Na channels –> depolarization and AP
At what length of a sarcomere do you get the most efficient tension?
1.8-2.0 um = maximal tension w/ all myosin heads bound to actin, actin isn’t overlapped
What does Troponin I have a strong affinity for?
actin
What is the range of sarcomere lengths that is physically functional in the body?
~1.65-2.25 um
What is retrograde transport?
from axon terminals back to cell body
At very short sarcomere lengths, what happens to relative tension and why?
tension decreases
too much overlap of actin and myosin; myosin gets scrunched up and some heads cant bind actin
How much ATP do you get from glycolysis?
How long does this last a muscle?
2 ATP + 2 NADH
1.3-1.6 minutes
Strength of muscles is determined by what?
size of muscle = increase in diameter, not number of fibers
How much ATP do you get from oxidative metabolism?
How long does this last a muscle?
36 ATP per glucose (i think)
theoretically forever - given O2 and nutrient supplies
What does Troponin C have a strong affinity for?
Ca
What is summation?
adding together of individual twitch contractions to increase intensity of overall muscle contraction
- increase # of motor units contracting at same time
- increase frequency of contraction
What is Rigor Mortis?
run out of ATP after death –> myosin head can’t exchange actin for ATP –> constantly stuck attached to actin in contracted position
eventually sarcomeres will break down and body will relax
What is the overall function of a troponin complex?
sits on tropomyosin
binds Ca –> triggers conformational change –> tropomyosin moves to expose myosin binding sites on actin
What is a DHP receptor?
dihydropyridine receptor
on T-tubule - when AP hits it changes conformation to signal RyR receptor to open and allow Ca release in muscle cell
What is defined as a motor unit?
all muscle fibers innervated by a single nerve fiber
What is the basic sequence of events of myosin walking/ratchet theory?
myosin head + ATP = resting state —> ATP hydrolyzed to ADP+Pi = cocked stated –> head binds actin –> Pi leaves –> power stroke –> binds new ATP and releases actin = relaxed state again
What are the 3 ways to regenerate ATP for muscles?
anaerobic glycolysis
creatine phophate
oxidative phosphorylation
What causes the exocytosis of neurotransmitter into the synaptic cleft?
AP –> voltage gated Ca channels open –> vesicles fuse w/ PM –> 125 vesicles released per AP
What is tetany?
point where a muscle is fully contracted and can’t recover bc stimulated so repetitively
What happens in you use up all your ATP in a muscle cell?
Can never exchange actin for ATP –> muscles permanently contracted
rigor mortis
What type of muscle is red?
slow twitch = high mitochondrial and myoglobin content
more capillaries = more blood = red
What is a Ryanodine (RyR) receptor?
receptor on sarcoplasmic reticulum that changes conformation after DHP changes conformation to allow Ca to be released from SR
AP –> DHP –> RyR –> ca release
What is anterograde transport?
from cell body to axon terminals
What 2 things help get Ca back into the SR after AP has passed?
ATP-dependent Ca pump = moves Ca into SR
Calsequestrin binds Ca = allows 40x more Ca to be stored
What type of muscle is white?
what are some of its characteristics?
fast twitch =
2x larger
2-3x more active phospocreatine and glycogen stores
How many hinges are on the head/neck of a myosin heavy chain?
3 total
Hinge 1 = where heads initially branch toward actin
Hinge 2 = on each individual head, allows them to move independently
At very long sarcomere lengths, what happens to the tension and why?
decreases bc no overlap of actin and myosin - heads cant contact actin to contract
Can a muscle have more than one nerve innervating it?
no!
What 2 parts of the sarcomere shorten during muscle contraction?
H zone
I band
What does Troponin T have a strong affinity for?
tropomyosin
How does phosphocreatine regenerate ATP?
How long does this provide muscle w/ ATP?
donates Pi to ADP –> ATP + creatine biproduct
8-10 seconds
