Bsf Exam 2: Smooth Muscle Physiology

Front 1

where is the nucleus in smooth muscle?

Back 1

centrally placed

Front 2

how are thin filaments arranged in smooth muscle?

Back 2

bundles attached to dense bodies (alpha-actin) on either side of sarcolemma or cytoskeleton, inter-digitated with thick filaments
(no sarcomeres!)

Front 3

what is the shape of a smooth muscle?

Back 3

spindle shaped
w/ indentations around outsides known as calveoli (Ca2+ "carports")

Front 4

how does the sarcoplasmic reticulum of smooth muscle differ from that of skeletal muscle?

Back 4

the SR of smooth muscle is poorly developed and sparse, no t-tubule or terminal cistenae so contraction requires extracellular calcium

Front 5

what regulates the SR of smooth muscle?

Back 5

ANS and hormones

Front 6

T/F
the cycling of myosin cross-bridges in smooth muscle are slower than skeletal muscle

Back 6

true

Front 7

why is there less energy required for smooth muscle?

Back 7

because there are fewer cycles and therefore less ATP to split

Front 8

how long does it take for smooth muscle to reach full contraction?

Back 8

.5 seconds

Front 9

how long does it take the smooth muscle to relax?

Back 9

1-3 or up to 30 seconds

Front 10

T/F
skeletal muscle has a higher force of contraction than smooth due to slow cross bridge cycling coupled with delayed response to Ca2+

Back 10

false

Front 11

what is the force of contraction for smooth muscle (numerically)?

Back 11

4-6 kg/cm2

Front 12

what is required for the initiation of contraction?

Back 12

calcium

Front 13

smooth muscle contains _____ which activates the ______ cross-bridges

Back 13

calmodulin; myosin

Front 14

how many calcium ions bind to calmodulin during activation of thick filaments?

Back 14

four

Front 15

what enzyme does the calmodulin calcium complex activate?

Back 15

Myosin light chain kinase (MLCK)

Front 16

as long as _____ is phosphorylated, ATPase activity in myosin is increased and the cross-bridge cycling can continue

Back 16

MLC

Front 17

instead of troponin, what serves as the intermediary in smooth muscle?

Back 17

Caldesmon and calponin

Front 18

what happens in smooth muscle when calcium ions are increased ?

Back 18

calmodulin forms a complex with Ca2+ which activates thin filaments by binding caldesmon and freeing myosin binding sites on actin

Front 19

what does epinephrine bind to in order to raise cAMP?

Back 19

B-adrenergic receptors

Front 20

Increase in cAMP leads to (contraction/relaxation) by inhibiting myosin light chain kinase

Back 20

relaxation

Front 21

where is the additional ATP necessary in the interaction with actin in the cross-bridge cycle of smooth muscle?

Back 21

phosphorylation at a specific site on a MLC

Front 22

what is a phasic contraction?

Back 22

a brief period of stimulation is associated with calcium mobilization followed by cross-bridge phosphorylation and cycling and cycling to produce a brief phasic, twitch like contraction

Front 23

what produces a tonic contraction?

Back 23

prolonged stimulation

Front 24

why is tonic contraction held at a reduced calcium concentration?

Back 24

to lower ATP consumption and lower shortening velocities while maintaining a constant force

Front 25

how many cross-bridge states does covalent regulation allow in smooth muscle?

Back 25

8

Front 26

Relaxation requires dephosphorylation of MLC, what dephosphorylates MLC in smooth muscle?

Back 26

Myosin light chain phosphatase

Front 27

what is the purpose of the latch mechanism?

Back 27

to maintain tonic contraction (after dephosphorylation of MLC) with reduced cross bridge cycling and has extremely low energy expenditure (eventual leads to relaxation)

Front 28

where is most of the calcium derived from in smooth muscle?

Back 28

extracellular fluid

Front 29

what is a multi-unit smooth muscle?

Back 29

each fiber can contract independently and is usually innervated by a single nerve ending (rare)

Front 30

why is neural integration important in multi-unit smooth muscles?

Back 30

the smooth muscle has no electrical coupling
(seldom spontaneous contractions)

Front 31

how are the fibers of a multi-unit smooth muscle insulated from each other?

Back 31

by a covering of collagen and flycoprotein fibrillae

Front 32

what are some examples of multi-unit smooth muscles?

Back 32

ciliary muscles of eye, iris, piloerector muscles

Front 33

what is a unitary smooth muscle?

Back 33

aggregates of hundreds or thousands of fibers that act as a single unit

Front 34

why are membranes adherent to one another in unitary smooth muscle?

Back 34

in order to transmit generated force

Front 35

how are the fibers of unitary smooth muscle connected?

Back 35

gap junctions

Front 36

because unitary smooth muscles are connected via gap junctions, _______ and ________ are simultaneous.

Back 36

action potential and contractions

Front 37

what are examples of unitary smooth muscle?

Back 37

walls of viscera, gut, bile ducts, ureters, uterus and many blood vessels

Front 38

what is the most common smooth muscle arrangement?

Back 38

single unit fashion

Front 39

what three things can initiate contraction of smooth muscles?

Back 39

1) intrinsic activity of pacemaker cells, 2) neurally released transmitter and 3) circulating or locally generated hormones or signaling molecules.

Front 40

in a somatic neuron, what is the pathway between the CNS and effector cell?

Back 40

monosynaptic
neuron releases ACh which binds to nicotinc receptor on the skeletal muscle cell

Front 41

what is released from the preganglionic neurons of the ANS?

Back 41

ACh
-binds a nicotinic receptor on postsynaptic membrane of the postganglionic neuron

Front 42

what is the postsynaptic receptor of parasympathetic ANS neurons?

Back 42

muscarinic

Front 43

is muscarinic ionotrophic or metabotrophic?

Back 43

metabotrophic

Front 44

what is the neurotransmitter for sympathetic postganglionic neurons?

Back 44

norepinephrine

Front 45

what is the receptor for the sympathetic postganglionic neuron?

Back 45

metabotropic, adrenergic receptor of 2 major subtypes alpha and beta

Front 46

what is the typical resting membrane potential of smooth muscle?

Back 46

-50 to -60mV

Front 47

what type of voltage gated Calcium channels does smooth muscle have?

Back 47

L-type

Front 48

T/F
calcium channels open slower and stay open longer allowing some cells to have plateaus in skeletal muscle

Back 48

false : in smooth

*in smooth Na+ has less participation in AP

Front 49

what does stretching of the visceral muscle muscle generate?

Back 49

spontaneous action potential

Front 50

Stretching of visceral smooth muscle may generate spontaneous action potentials via ___________

Back 50

stretch-activated cation-permeable channels

Front 51

what inhibits smooth muscle contractions in the gut, but stimulates contraction in vascular smooth muscle?

Back 51

norepi

Front 52

what does alpha 1 couple with in smooth muscle? what does their coupling result in?

Back 52

Gq; increased cellular calcium which results in smooth muscle contraction

Front 53

what does alpha 2 couple with in smooth muscle? what does their coupling result in?

Back 53

Gi; decreased cAMP activity which results in smooth muscle constriction and neurotransmitter inhibition

Front 54

what does beta 1 couple with in heart muscle?
what does their coupling result in?

Back 54

Gs; increased cAMP which results in heart muscle contraction

Front 55

what does beta 2 couple with in smooth muscle? what does their coupling result in?

Back 55

Gs; increased cAMP which results in smooth muscle relaxation

Front 56

what is the agonist potency order for alpha 1 receptor and what is the mechanism?

Back 56

norepi>epi>>isoprenaline; phospholipase C activated, IP3, and calcium up

Front 57

what is the agonist potency order for alpha 2 receptor and what is the mechanism?

Back 57

epi>norepi>>isoprenaline; adenylate cyclase inactivated, cAMP down

Front 58

what is the agonist potency order for beta 1 and 2 receptor and what is the mechanism?

Back 58

isoprenaline>epi>>norepi; adenylate cyclase activated, cAMP up

Front 59

what are maximal shortening velocities with no load directly dependent on>

Back 59

cross-bridge phosphorylation by MLCK

Front 60

near maximal stress can be generated with only _____ to _____ of cross-bridges in the phosphorylated state

Back 60

20-30%

Front 61

What is the purpose of stress relaxation in smooth muscle?

Back 61

allows hollow organs to expand and contract as needed (filling/emptying of bladder etc)

Front 62

What type of action potentials are generated by pacemaker cells

Back 62

slow wave potentials

Front 63

What are some ways that smooth muscle contraction can be induced w/o an action potential?

Back 63

1. oscillations in Vm
2. hormones and neurotransmitters use second messengers to increase Ca2+ release from SR

Front 64

3 sources of calcium in smooth muscle

Back 64

1. voltage gated L type channel Ca2+ channel
2. SR released w/o depolarization
3. Ca2+ entry via non voltage-gated channel

Front 65

Blood flow control in smooth muscles is via what factors that cause vasodilation (3)?

Back 65

1. lack of O2
2. excess CO2
3. increased H+