Muscle 2 (ADD)

Question 1

What is cardiac muscle made up of?

Answer 1

-cardiomyocytes
-myocytes are shorter + more branched
-intercalated disks - where myocytes join together

Question 2

How do cardiomyocytes appear?

Answer 2

Striated

Question 3

How is each cardiac muscle cell coupled to its neighbour?

Answer 3

-electrically
-by gap junctions

Question 4

Is smooth muscle striated or non-striated?

Answer 4

Non-striated

Question 5

How is intracellular calcium increased in skeletal muscle?

Answer 5

-depolarisation activates L-type calcium channels in T-tubule membrane to open
-influx of calcium into cell
-causes mechanical tethering between L-type calcium channels in T tubules + calcium release channels (ryanodine receptors) in SR membrane
-calcium release channels in SR open and calcium moves into cytoplasm

Question 6

How is intracellular calcium increased in cardiac muscle?

Answer 6

-have T tubules, but only close to 1 branch of SR - Dyad
-lie at Z line region of sarcomere
-no mechanical interaction between voltage gated calcium channels in T-tubule + Ryanodine receptors in SR
-influx of calcium through T-tubules activates ryanodine receptors (calcium induced calcium release - CICR)

Question 7

How is intracellular calcium increased in smooth muscle?

Answer 7

-no T-tubules + Triad/Dyad structure, have shallow invaginations (cave)
-peripheral SR encircles caveolae
-central SR runs through cell
-changes in action potential can activate L-type calcium channels
-leads to CICR via activation of ryanodine receptors in SR membrane
-activation of Gq coupled receptors leads to IP3 production + stimulation of IP3 receptors in SR membrane

Question 8

How is calcium removed from calcium terminated muscle contraction?

Answer 8

-removed from cytoplasm
-across cell membrane by means of plasma membrane calcium ATPase (PMSA) or electrogenic sodium/calcium exchanger (NCX)
-back into SR via sarco/endoplasmic reticulum ATPase

Question 9

How does the sarcomere contract?

Answer 9

-calcium binding occurs on troponin complex
-initiates a change in shape of the molecules, exposing binding sites
-myosin head has high ATPase activity but very low at resting conditions

Question 10

How does contraction occur in smooth muscle?

Answer 10

-no troponin in smooth muscle (calponin + caldesmon inhibit myosin-actin interaction)
-contraction involves stimulation of calmodulin by calcium
-calmodulin activated myosin light chain kinase, which phosphorylates MLC
-removes inhibitory effects of calponin + caldesmon
-allows crossbridge formation and contraction

Question 11

How is contraction stopped in the smooth muscle?

Answer 11

Must dephosphorylate MLC which involved light chain phosphatase (MLCP)