Contractile mechanisms

Question 1

What are the three types of muscles?

Answer 1

Skeletal
Cardiac
Smooth

Question 2

What is contraction?

Answer 2

Contraction is the interaction of actin and myosin fueled by ATP and driven by rise in [Ca2+]

Question 3

Skeletal vs Cardiac vs Smooth

Striation

Answer 3

Smooth not striated whereas skeletal and cardiac are

Question 4

Skeletal vs Cardiac vs Smooth

Answer 4

Skeletal have many nucleus

Cardiac usually have one nucleus

Question 5

What do both skeletal and cardiac muscles have?

Answer 5

Have T-tubules

Question 6

What are T-tubules?

Answer 6

T-tubules are cell membranes that extend deep into cell interior

Question 7

What do T-tubules interact with?

Answer 7

Interact with sarcoplasmic reticulum

Question 8

How are skeletal muscles organised?

Answer 8

Thick filaments made up of myosin
Thin filaments made up of actin
Where two filaments overlap, seen as dark region

Question 9

What is depolarization initiated by?

Answer 9

Depolarisation initiated by nAchr

Question 10

What is depolarization maintained by?

Answer 10

Maintained by Na+ channels

Question 11

What is there within the T-tubules?

Answer 11

Within t-tubules, there are voltage sensing ion channels like proteins which physically interact with Ca2+ in sarcoplasmic reticulum

Question 12

What is the calcium release channel called?

Answer 12

Ryanodine receptor

Question 13

What do ryanodine receptors interact with?

Answer 13

Ryanodine receptors interact with DHP

Question 14

What are DR channel proteins?

Answer 14

Ion channel that doesn’t conduct ions

Question 15

Why are DR channels known as this?

Answer 15

So called because it is blocked by DHP that are well known calcium channel blockers

Question 16

Brief overview of contractile mechanism

Answer 16

Tropomyosin lying on actin covering myosin binding site

Calcium binds to troponin and conformational change occurs and myosin binding site on actin is exposed

Question 17

Contractile cycle(Priming of myosin head)

Answer 17

ATP hydrolysed by ATPase present on myosin head

Cocking of myosin head

Question 18

Contractile cycle(Power stroke with actin)

Answer 18

Power stroke occurs and ADP is released
Myosin undergoes conformational change
Actin moves towards centre of sarcomere

Question 19

Contractile cycle(Relaxation of acto-myosin complex

Answer 19

ATP binds to myosin head causing cross bridge to break and myosin head detaches from actin

Question 20

How does contraction occur in cardiac muscles?

Answer 20

Ion channels in T-tubules pump out Ca2+ into cell
Increased [Ca2+] results in calcium induced calcium release from RyR2
Lead to contraction

Question 21

Skeletal vs Cardiac

Answer 21

Skeletal:Physical interaction between DHP and RyR
Cardiac:Opening calcium channel promotes CICR

Question 22

What are smooth muscles not in?

Answer 22

Contractile proteins not in regular arrays:

Not striated

Question 23

What do smooth muscles not have?

Answer 23

Don’t have a T-tubule system

Question 24

Smooth muscles have a less developed…

Answer 24

Less developed SR

Question 25

What are smooth muscles able to sustain?

Answer 25

Sustain contraction for longer periods

Question 26

What do myofilaments in smooth muscle connect with?

Answer 26

Myofilaments connect with dense bodies

Question 27

What is present instead of troponin?

Answer 27

No troponin but caldemson and calponin

Question 28

What does tropomyosin not interact with?

Answer 28

Tropomyosin doesn't interact with myosin binding site

Question 29

Difference between the myosin in smooth and skeletal muscles

Answer 29

Myosin in smooth muscles is a different isoform than skeletal muscles

Question 30

What does myosin have a lower of?

Answer 30

Lower ATPase activity | Lower affinity for ATP

Question 31

Contraction of smooth muscle

Answer 31

Increased calcium Calcium binds to calmadulin Activates myosin light chain kinase which phosphorylates myosin at light chain

Question 32

What does activation of myosin light chain kinase do?

Answer 32

Phosphorylates regulatory MLC at Ser 19 Increases ATPase activity of myosin lead by 1000x Alters structure of myosin

Question 33

Relaxation of smooth muscle and comment on the dephosphorylatoin of myosin

Answer 33

[Ca2+] drops MLCK becomes inactive MLCP removes phosphate from Ser 19 But dephosphorylated myosin has a low ATP affinity Latch state and slow release of actin from myosin

Question 34

Smooth muscle vs skeletal muscle

Answer 34

``` Greater shortening in smooth Slower speed of contraction in smooth Lower energy requirement in smooth Greater force generation in smooth Latch state due to myosin having low ATP affinity ```