Excitation-Contraction Coupling

Question 1

What is the purpose of subneural clefts?

Answer 1

increase surface area on post-synaptic cleft so there are more receptors available

Question 2

After repolarization, what happens to DHP and RyR?

Answer 2

DHP changes back to original shape first –> then RyR goes back too

Question 3

What type of muscle would have more nerve fibers in it?

Answer 3

smaller, more precise muscles - allows it to have more control

Question 4

Once the ACh has been released into synaptic cleft, what happens to the post-synaptic membrane (nicatinic receptor)?

Answer 4

ACh goes to nAChR –> allows Na into cell –> more + in cell–> triggers voltage-activated Na channels –> depolarization and AP

Question 5

At what length of a sarcomere do you get the most efficient tension?

Answer 5

1.8-2.0 um = maximal tension w/ all myosin heads bound to actin, actin isn’t overlapped

Question 6

What does Troponin I have a strong affinity for?

Answer 6

actin

Question 7

What is the range of sarcomere lengths that is physically functional in the body?

Answer 7

~1.65-2.25 um

Question 8

What is retrograde transport?

Answer 8

from axon terminals back to cell body

Question 9

At very short sarcomere lengths, what happens to relative tension and why?

Answer 9

tension decreases

too much overlap of actin and myosin; myosin gets scrunched up and some heads cant bind actin

Question 10

How much ATP do you get from glycolysis?

How long does this last a muscle?

Answer 10

2 ATP + 2 NADH

1.3-1.6 minutes

Question 11

Strength of muscles is determined by what?

Answer 11

size of muscle = increase in diameter, not number of fibers

Question 12

How much ATP do you get from oxidative metabolism?

How long does this last a muscle?

Answer 12

36 ATP per glucose (i think)

theoretically forever - given O2 and nutrient supplies

Question 13

What does Troponin C have a strong affinity for?

Answer 13

Ca

Question 14

What is summation?

Answer 14

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

Question 15

What is Rigor Mortis?

Answer 15

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

Question 16

What is the overall function of a troponin complex?

Answer 16

sits on tropomyosin

binds Ca –> triggers conformational change –> tropomyosin moves to expose myosin binding sites on actin

Question 17

What is a DHP receptor?

Answer 17

dihydropyridine receptor

on T-tubule - when AP hits it changes conformation to signal RyR receptor to open and allow Ca release in muscle cell

Question 18

What is defined as a motor unit?

Answer 18

all muscle fibers innervated by a single nerve fiber

Question 19

What is the basic sequence of events of myosin walking/ratchet theory?

Answer 19

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

Question 20

What are the 3 ways to regenerate ATP for muscles?

Answer 20

anaerobic glycolysis
creatine phophate
oxidative phosphorylation

Question 21

What causes the exocytosis of neurotransmitter into the synaptic cleft?

Answer 21

AP –> voltage gated Ca channels open –> vesicles fuse w/ PM –> 125 vesicles released per AP

Question 22

What is tetany?

Answer 22

point where a muscle is fully contracted and can’t recover bc stimulated so repetitively

Question 23

What happens in you use up all your ATP in a muscle cell?

Answer 23

Can never exchange actin for ATP –> muscles permanently contracted
rigor mortis

Question 24

What type of muscle is red?

Answer 24

slow twitch = high mitochondrial and myoglobin content

more capillaries = more blood = red

Question 25

What is a Ryanodine (RyR) receptor?

Answer 25

receptor on sarcoplasmic reticulum that changes conformation after DHP changes conformation to allow Ca to be released from SR
AP –> DHP –> RyR –> ca release

Question 26

What is anterograde transport?

Answer 26

from cell body to axon terminals

Question 27

What 2 things help get Ca back into the SR after AP has passed?

Answer 27

ATP-dependent Ca pump = moves Ca into SR

Calsequestrin binds Ca = allows 40x more Ca to be stored

Question 28

What type of muscle is white?

what are some of its characteristics?

Answer 28

fast twitch =
2x larger
2-3x more active phospocreatine and glycogen stores

Question 29

How many hinges are on the head/neck of a myosin heavy chain?

Answer 29

3 total
Hinge 1 = where heads initially branch toward actin
Hinge 2 = on each individual head, allows them to move independently

Question 30

At very long sarcomere lengths, what happens to the tension and why?

Answer 30

decreases bc no overlap of actin and myosin - heads cant contact actin to contract

Question 31

Can a muscle have more than one nerve innervating it?

Answer 31

no!

Question 32

What 2 parts of the sarcomere shorten during muscle contraction?

Answer 32

H zone

I band

Question 33

What does Troponin T have a strong affinity for?

Answer 33

tropomyosin

Question 34

How does phosphocreatine regenerate ATP?

How long does this provide muscle w/ ATP?

Answer 34

donates Pi to ADP –> ATP + creatine biproduct

8-10 seconds