Muscle Physiology

Question 1

what are the steps in excitation-contraction coupling?

Answer 1

1) AP at neuromuscular junction
2) calcium release
3) myosin and actin interaction
4) muscle contraction
5) calcium removal
6) relaxation

Question 2

what is excitation-contraction coupling? ie neuromuscular transmission

Answer 2

electrical stimulus (action potential) is converted into a mechanical response (contraction)

Question 3

what is step 1 of the excitation-contraction coupling?

Answer 3

the action potential at neuromuscular junction

is a chemical synapse –> activation opens calcium channels

opening of ACh receptors results in an EPP –> depolarizes the membrane and initiates action potential

Question 4

what is the end plate potential and what does it depend on?

Answer 4

is a graded potential confined (localized) to the motor end plate

depends on the amount and duration of ACh at the end plate

Question 5

what are some factors that affect the magnitude of the EPP?

Answer 5

-amount of ACh that is released
-voltage gated Ca channels
-activity of esterase
-agonist/antagonists that act on the receptor

Question 6

what is step 2 of excitation-contraction coupling?

Answer 6

calcium release

depolarization of transverse tubules (T-tubules)
the AP travels through the entire sarcolemma and into the T tubules

Question 7

what are the steps in calcium release from SR?

Answer 7

1) membrane depolarization opens L-type Ca channel
2) mechanical coupling between the L-type Ca channel and the Ca release channel causes the Ca release channel to open
3) Ca exits the SR via the Ca release channel and activates troponin C, leading to muscle contraction

Question 8

what is step 3 in excitation-contraction coupling?

Answer 8

arrangement of actin and myosin filaments in a sarcomere

Question 9

what are thin filaments (actin) made up of?

Answer 9

actin
tropomyosin
troponin

Question 10

what does tropomyosin do?

Answer 10

inhibits binding of myosin to actin

Question 11

what is troponin?

Answer 11

calcium sensitive molecular switch

Question 12

what is the role of calcium in the regulation of myosin binding to actin?

Answer 12

allows for physical repositioning of the tropomyosin filament, which exposes myosin binding site on the actin molecules

Question 13

what are steps 5 and 6 in excitation-contraction coupling?

Answer 13

-calcium is removed from the ICF back into the SR by the SR atpase (SERCA)

-and from ICF to ECF via a sarcolemmal Ca ATPase and by a Ca/Na exchanger