lecture 33 - Smooth muscle Flashcards Preview

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Flashcards in lecture 33 - Smooth muscle Deck (27):
1

sarcomeres in smooth muscle?

no such thing.

2

t-tubules in smooth muscle?

there are NO t-tubules, the equivalent is CAVEOLAE

3

regulatory protein

calmodulin (not troponin/tropomyosin)

4

Is there a sarcoplasmic reticulum in smooth muscle?

yes, but it is minimal

5

smooth muscle size and shape

30-200μm x 3-8μm spindle shaped

6

which muscle is the most common in the human body?

smoooooooooooooooooooooth

7

single-unit smooth muscle

group of muscle cells, acting as one unit due to gap junctions between individual cells, innervated by an autonomic neuron

8

multi-unit smooth muscle

each cell woks by itself, innervated by an autonomic neuron mesh

9

Varicosities

bulge-thingies in the autonomic neuron which releases neurotransmitters

10

smooth muscle arrangement in the GI tract

layer of smooth muscle running longitudinal and another layer running transverse at right angles to it.

11

dense bodies

replace z-lines - anchor actin to the sarcolemma

12

intermediate filaments (in the context of smooth muscle)

cytoskeleton element. Wrap the myocyte in a diamond pattern like a mandarin bag

13

how do smooth muscles change in length compared to skeletal muscle?

they can change in length more than skeletal muscle

14

striations in smooth muscle?

nah none of that, but they still contain actin and myosin - less organised though

15

complex electrical behaviour, can be _______, _______, or __________ (=myogenic). For example, - myogenic with _____ _____ of depolarisation (e.g. gut) - ______ induced contraction (e.g. iris)

complex electrical behaviour, can be _neural_, _hormonal_, or _spontaneous_ (=myogenic). For example, - myogenic with _slow_ _wave_ of depolarisation (e.g. gut) - _neurally_ induced contraction (e.g. iris)

16

what is the trigger for contraction in smooth muscle?

contraction in smooth muscle is ALWAYS caused by an increase in cytosol [Ca2+]

17

how do calcium ions enter the cytosol?

- move in from the extracellular fluid by voltage-dependent/-independent (any way it wants) - or from the scant SR via IP3 (NOT Calcium induced)

18

once entering the cytosol, the Ca2+...

binds to and activates calmodulin (1 calmodulin binds 4 Ca2+)

19

activated calmodulin...

activates the myosin light chain kinase enzymes, phosphorylating the light chains (e.g. LC20) located on the neck of the myosin

20

activated MLCK ...

activates the myosin ATPases

21

activated myosin ...

forms cross-bridges with actin, as per usual

22

maximum rate of cross-bridge formation =

low, therefore slow contractions

23

what happens for the smooth muscle to relax again

1. drop in Ca2+ (caused by CaATPase removing it from the cell) will inactivate MLCK = less phosphorylating 2. Phosphatase is required to dephosphorylate the myosin light chain

24

how is contraction in smooth muscle graded?

by a balance between MLCK and phosphatase enzymes. More Phosphatase = relaxation more MLCK = contraction

25

cAMP impact on contractions in smooth muscle

inhibits MLCK = less contractions

26

how does smooth muscle respond to being stretched?

initially contracts to resist the stretch (stretch activated Ca2+ channels increases force). They then relax slowly, adapting to the change in length (via calcium dependant K+ channels).

27

sumarise each step 

Q image thumb

  1. Increased intracellular Ca2+

  2. Calmodulin activation

  3. Activation of calmodulin dependent protein kinase (myosin light chain kinase)

  4. Phosphoralisation of myosin

  5. Actin /myosin interaction resulting in contraction