Week 15: Physiology of Smooth muscle

Question 1

what muscle types are voluntary?

Answer 1

skeletal

Question 2

What muscle types are striated?

Answer 2

skeletal and cardiac

Question 3

What muscles types are part of the autonomic innervatio?

Answer 3

smooth and cardiac

Question 4

What are striations due to?

Answer 4

organisation of a contractile proteins in individual muscle fibres
actin and myosin proteins= orderly

Question 5

What are the key features of skeletal muscle?

Answer 5

Individual muscle fibres are large, elongated, cylindrical and possess multiple nuclei

Question 6

What are the key features of cardiac muscle?

Answer 6

Individual muscle fibres are large, cylindrical and possess multiple nuclei

Question 7

What are the key features of smooth muscle?

Answer 7

Individual muscle fibres are relatively small, spindle shaped, and possess one nucleus

Question 8

What neurones are involved in skeletal muscle?

Answer 8

alpha and gamma neurone

Question 9

What fibres are involved in cardiac and smooth muscle?

Answer 9

sympathetic and parasympathetic postganglioic fibres

Question 10

Where is smooth muscle mostly found?

Answer 10

walls of hollow organs and tubes

Question 11

What does smooth muscle mediate?

Answer 11

propulsive movements and exerting pressure

Question 12

What are the 2 classes of smooth muscle?

Answer 12

phasic & tonic

Question 13

What is phasic smooth muscle?

Answer 13

muscle exhibits rhythmic or intermittent activity

Question 14

What is tonic smooth muscle?

Answer 14

muscle that is continuously active

Question 15

What is an example of a phasic smooth muscle that is phasically active?

Answer 15

phasically active

stomach intestines underlies peristalsis

Question 16

What is an example of a tonic smooth muscle usually in contracted state?

Answer 16

normally contracted
sphincter
prevent faeses from rectum to anal canal

Question 17

What is an example of a phasic muscle normally in the relaxed state?

Answer 17

normally relaxed

oesophagus, urinary bladder

Question 18

What is an example of tonic smooth muscle?

Answer 18

normally partially contracted

blood vessels, airways

Question 19

What can smooth muscles also be classified as?

Answer 19

• Single unit (connected by gap junctions)

- Multiunit ( muscle cells are not electrically coupled, activity in one cell does. not results in activity in another)

Question 20

What does the single unit smooth muscle stimulate?

Answer 20

wave contraction across a muscle sheet

only stimulated by one type of neurone

Question 21

What does the multiunit smooth muscle stimulate?

Answer 21

individual muscle fibres

Question 22

What allows finer control of smooth muscle, multiunit or single unit?

Answer 22

multiunit

stimulated by parasympathetic and sympathetic post ganglionic neurones

Question 23

What are the muscles which a single unit smooth muscle will stimulate?

Answer 23

stomach, intestines, urinary bladder, airway smooth muscle

Question 24

What are the muscles which a multiunit smooth muscle will stimulate?

Answer 24

iris, vas deferens

Question 25

What type of filament does smooth muscle contain?

Answer 25

myosin, actin & intermediate

Question 26

What proteins form most of the intermediate filament in smooth muscle?

Answer 26

desmin and vimentin

Question 27

What does the actin of smooth muscle lack?

Answer 27

contains tropomyosin but lacking troponin | Where does Ca2+ bind

Question 28

What structure is important in maintaining the shape of the cell?

Answer 28

intermediate filaments

Question 29

What direction do actin filaments run?

Answer 29

parallel to the long axis of the cell

Question 30

Why is the smooth muscle unorderly and unstriated?

Answer 30

filaments do not form myofibrils | no sarcomere patternNo Z line

Question 31

With no Z line in. smooth muscle, where do actin filaments bind to?

Answer 31

attach to dense bodies in the cytoplasm and dense bands at the inner surface of the plasmalemma

Question 32

What contains more actin skeletal or smooth?

Answer 32

smooth

Question 33

How does contraction occur in smooth musc;e?

Answer 33

very similar to skeletal (cross bridge + Ca2+ dependent) | Apart from the contraction is over dense band to dense body to the other dense band

Question 34

What does Ca2+ bind to?

Answer 34

calmodulin in the cytoplasm

Question 35

What is the change in Ca2+ conc. from a maximal contraction to occur?

Answer 35

100nM to 1 microM | up 10 fold

Question 36

what does Ca2+-calmodulin activate?

Answer 36

MLCK enzyme

Question 37

What does active MLK permit?

Answer 37

the transfer of organic phosphate to the myosin head

Question 38

What is required for actin to myosin binding?

Answer 38

ATP

Question 39

Why is additional ATP required in contraction?

Answer 39

ATP is required for cross bridge cycling to continue via hydrolysis

Question 40

What is calmodulin? Where is it found in a cell?

Answer 40

multifunctional Ca2+ binding protein | present in the cytoplasm of all eukaryotic cells

Question 41

What happens when 2 or more Ca2+ molecules bind to calmodulin?

Answer 41

undergoes a large confo change | the strand under the 2 lobes to become an alpha helix

Question 42

Where does Ca2+ bind to on calmodulin?

Answer 42

2 Ca2+ binds to EF hand motifs 4Ca2+ per calmodulin called CaM

Question 43

What can CaM bind to?

Answer 43

vast range of kinase peptides | e.g. CaM kinase

Question 44

What does CaM activate?

Answer 44

MLCK

Question 45

Is calcium calmodulin an enzyme?

Answer 45

NO

Question 46

What is activated in smooth muscle contraction?

Answer 46

myosin

Question 47

What can smooth muscle contraction be called?

Answer 47

myosin based contraction

Question 48

How does contraction occur in smooth muscle?

Answer 48

phosphorylation of the regulatory myosin light chain (MLC) in the presence of elevated intracellular Ca2+ (and ATP)

Question 49

How does relaxation occur of smooth muscle?

Answer 49

dephosphorylation of MLC by myosin phosphatase which has constitutive activity, but is also regulated

Question 50

What chain in phosphorylated in myosin?

Answer 50

light chain

Question 51

What is the differnece between MLCK and MP?

Answer 51

MLCK phosphorylates MLC | MP de-phosphorylates MLC

Question 52

What autonomic innervation do arteries primarily receive?

Answer 52

sympathetic (NA) adrenoR

Question 53

What autonomic innervation do other tissue receive?

Answer 53

symp and para innervation(ACh, muscarinic)

Question 54

What autonomic innervation occurs in the G.I tract?

Answer 54

enteric/ANS

Question 55

What tissue have no autonomic innervation?

Answer 55

uterus

Question 56

Where does chemical transmission between autonomic neurones and smooth muscle take place? The junction between postganglionic fibre

Answer 56

neuroeffector junctions

Question 57

What are varicosities?

Answer 57

where the transmitter is released from. many of them along nerve fibre

Question 58

What factors can increase/decrease smooth muscle activity?

Answer 58

- Hormones - Autonomic neurotransmitter - Pacemaker activity of smooth muscle itself - Many therapeutically important drugs

Question 59

What can increase [Ca2+]?

Answer 59

- Ca2+ influx from the extracellular fluid by cell-surface voltage-activated Ca2+ channels opened by membrane depolarisation - Release of Ca2+ from intracellular stores, typically as a result of the activation of cell surface G protein-coupled receptors (GPCRs)

Question 60

What is pharmacomechanical coupling?

Answer 60

-Processes by which an agent causes a change in smooth muscle tone without a change in membrane potential

Question 61

What does a secondary messenger do in pharmacomechanical coupling?

Answer 61

-That either contract, or relax, the muscle

Question 62

What are the important secondary messengers in pharmacomechanical coupling?

Answer 62

- Inositol trisphosphate (IP3) causing contraction | - (cGMP) and cyclic adenosine monophosphate (cAMP), both causing relaxation

Question 63

What processes can E-C coupling be described as?

Answer 63

``` Pharmacomechanical coupling Electromechanical coupling (in reality the 2 overlap to some extent) ```

Question 64

What us electromechanical coupling?

Answer 64

opening of plasma membrane voltage-activated L-type Ca2+ channels in response to depolarization with, or without, action potential generation

Question 65

In pharmacomechanical coupling in smooth muscle how is Ca2+ released into the SR?

Answer 65

IP3 – generated by activation of PLC opens IP3 receptors in the SR membrane releasing Ca2+

Question 66

In electromechanical coupling what does the released Ca2+ bind to?

Answer 66

-Opening of Ca2+-activated chloride channels (CaCC) -Ca2+ in to cell causing depolarisation OR// binds to CaM= contraction

Question 67

What does DAG bind to and activate/ inhibit?

Answer 67

Inhibit K+ channel directly or activate PKC to then inhibit the channel (keep positive charge in) -Na/Ca channel, Ca2+ in to cell

Question 68

What does the depolarisation in electromechanical coupling lead to?

Answer 68

Opens voltage-activated L-type Ca2+ channels, further increasing [Ca2+]i and contraction (4)

Question 69

What 2 mechanisms decreases Ca2+ levels and cause relaxation?

Answer 69

pumped back into SR via a Ca2+ ATPase (SERCA) | Pumped out of cell via Na/Ca exchanger or Ca2+ ATPase