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Flashcards in Smooth muscle innervation Deck (47)
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1

What is the rough Em of smooth muscle cells?

-50mV

2

Compare APs in smooth and skeletal muscle

Smooth - Slower upstroke and last longer

3

What current drives depol in SMC?

L Ca2+ current

4

What repolarises smooth muscle cells?

Ca2+ activated K+ channel and VGKC

5

Why is SM nerve transmission described as "en passant"

APs pass along neurone across each varicosity releasing neurotransmitter into synaptic cleft

6

How is visceral SM similar to SAN?

Can exhibit pacemaker activity

7

Describe what triggers contraction in single unit SM?

Pacemaker cells - spontaneous contraction.

Modified by ANS and neurotransmitters etc

8

Describe what triggers activation of multiunit SM?

Motor neurones (contraction initiated by neurotransmitter)

9

True of false, VGNC drives SM action potential?

False, it's Ca2+ (L type)

10

How do SM open SR (what mechanism)?

Intracellular signals, i.e. secondary messenger system

11

What are 3 mechanism for Ca2+ increase in SM?

Ligand gated ion channel

Ca2+ via L type channel (NA = agonist and depolarise cell membrane)

IP3 mediated Ca2+ release from SR

12

Instead of troponin, what initiates contraction in SM?

Myosin phosphorylated which activates its ATPase ability

13

Does SM need changes in Em for contraction?

No

14

What does tropomyosin do at rest?

Blocks myosin binding site, stabilises actin

15

What is functionally similar to troponin?

Caldesmon - regulates position of tropomyosin

16

Describe structure of myosin

2 heavy chains, 4 light chains head, hinge and tail region

17

Which part of myosin forms cross bridge with actin?

Head

18

What part of myosin has ATPase activity?

Head

19

In absence of Ca2+ what prevent actin myosin binding?

Myosin light chain (not tropomyosin)

20

True or false, tropomyosin stops actin myosin binding when Ca2+ absent (SM)?

False, it's Myosin light chain

21

How many Ca2+ bind to calmodulin?

4

22

What does Ca2+ bind to?

Calmodulin

23

What 3 things does CalCam act on, what are the effects?

Activates MLCK - MLCK phosphorlylates P light chain of myosin (MLC)

CalCam acts on caldesmon removes inhibition of tropomyosin

Calcam binds to calponin -removes inhibiton on myosin head ATPase activity

24

Which part of myosin regulates cross bridge cycling?

P light chain

25

What happens after MLC phosphorylated?

Relieves MLC inhibition and ATP hydrolysed by myosin head and cross bridge cycling occurs

26

What happens in relaxation?

Dephos of MLC by MLCP when Ca2+ falls

27

What are the roles of PKA and PKG in smooth muscle relaxation on MLCK?

Phophorylate MLCK (inactive)

Reduce Ca2+ sensitivity of MLCK - more calcium calmodulin needed to activate it

Promote relaxation

28

How do PKA and PKG promote relaxation?

Phosphorylate/desensitise MLCK

Phosphorylate K+ channel to hyperpolarise membrane inhibits Ca2+ entry

29

What are the roles of calponin and caldesmon (how do they compare to troponin/tropomyosin)?

Caldesmon (tropomyosin) and calponin (inhibits heads ATPase activity)

30

What does DAG subunit do to release Ca2+/promote contraction?

DAG, along with Ca2+, activates protein kinase C (PKC) which promotes contraction/Ca2+ entry