Dr. Karius Excitation Contraction Coupling 1

Question 1

motor unit =

Answer 1

one alpha motor neuron and all the muscles it innervates

Question 2

Vm of a motor cell =

Answer 2

-80 – -90 mV

Ca++ is in low concentration at this point
micromolar range
sequestered in sarcoplasmic reticulum

Question 3

Triad =

Answer 3

terminal cisterna, TWO SRs and T tubule

only in skeletal muscle

a diad is in cardiac muscle

Question 4

Sequence of events leading to calcium release in skeletal muscles

Answer 4

1. depolarization comes down T tubule
2. DHP channel
3. DHP causes Ryanodine receptor to open and release Ca stored in the terminal cisterna
4. calcium binds to troponin C and initiated contracture
5. Ca dependent ATPase mediate return of Ca into the SR
6. within the SR, Ca binds to Calsequestrin, which prevents it from diffusing out

Question 5

terminal cisternae =

Answer 5

the sarcoplasmic reticulum inside the muscle cell

Question 6

DHP receptor

Answer 6

voltage and ligand gated, effected by both but during muscle contraction only voltage matters
DHP is one possible ligand but doesnt occur in the body naturally

Question 7

Ryanodine receptors

Answer 7

we dont know what causes it to work

voltage AND ligand gated, effected by both
no the SR membrane and coupled to the DHP receptor
the chemical ligand is ryandoine
ryanodine is a poison

Question 8

what does ryanodine do to a receptor?

Answer 8

causes it to be permanently open

Question 9

cannabis

Answer 9

unknown receptor

appetite control

Question 10

ryanodine receptor is helped by trace amounts of

Answer 10

calcium

Question 11

so what effects the ryanodine receptor?

Answer 11

calcium, voltage, conformational change

Question 12

myosin is bound to what at rest?

Answer 12

M-ADP-Pi

adp and inorganic phosphate

when not contracting, it’s associated with those two
affinity for actin is HIGH but the TROPOMYOSIN covers actin

Question 13

how does calcium work?

Answer 13

it becomes high in the myofibril region. calcium binds to troponin C, causing conformational change and allows it to pull tropomyosin out of the way. = active sites on actin exposed

Question 14

What part of the myosin has the atp head?

Answer 14

the head

it’s a contractile protein with ATPase

Question 15

what happens when ATP binds to myosin head?

Answer 15

it causes a conformational change in the myosin head to dissociate from the actin

Question 16

ATP and myosin

Answer 16

ATP causes the myosin to be “cocked and ready” for th power stroke, but when it actually DOES the powerstroke it is a myosin–ADP–Pi complex

Question 17

after the active site on actin is exposed, what are the following steps?

Answer 17

binding of myosin--ADP--Pi
powerstroke
Release of ADP-Pi
binding of atp to myosin actin complex
dissociation of myosin from actin
"re-clocking" of myosin head

Question 18

how long will the “power stroke” process work?

Answer 18

until no more action potential
no more release of Ca
Ca-ATPase removes Ca from cytoplasm

Question 19

where does skeletal muscle get its ATP?

Answer 19

Creatine phosphate

Question 20

what does a creatine phosphate do for the ATP supply?

Answer 20

it donates a phosphate group to the spend ADP

Question 21

CrP + ADP –>

Answer 21

Cr + ATP

Question 22

what are thesources of energy for skeletal muscle

Answer 22

Creatine phosphate AT myosin

ATP from aerobic and anaerobic respiration and fatty acid degradation

Question 23

Failure to maintain energy supply causes…

Answer 23

fatigue
depletion of ACh at NMJ
inadequate ATP

Question 24

CrP activity

When, where, why

Answer 24

at myofibril
1:1 CrP–ATP ratio
appears as energy source during exercise

Question 25

Aerobic energy supply

when, where, why

Answer 25

mitochondria produced
38 ATP
occurs at rest

Question 26

Anaerobic energy supply

when, where, why

Answer 26

cytosol
2 ATP
during intense activity