Smooth Muscle Physiology

Question 1

Do we see more actin in smooth muscle or skeletal muscle?

Answer 1

Much more actin in smooth muscle

(There is a lot more myosin in skeletal muscle)

Question 2

Where does most of the calcium for contraction of a smooth muscle cell come from?

Answer 2

Outside the cell (not the sarcoplasmic reticulum)

Question 3

What are the three methods for getting calcium out of a smooth muscle cell (that were covered in class)?

Answer 3

SERCA

Sodium / Calcium antiporters

Sarcolemmal Ca2+ ATPase

Question 4

What does calcium bind to in smooth muscle cells to initiate a contraction?

Answer 4

Calmodulin

Question 5

What is activated by Calmodulin after it binds to calcium?

Answer 5

Myosin light chain kinase

(Phosphorylates myosin light chains)

Question 6

What are the functions of angiotensin II, vasopressin, and endothelin I?

Answer 6

They contract smooth muscle

Question 7

What is the function of adenosine on smooth muscle?

Answer 7

Relaxes smooth muscle

Question 8

What ion is primarily responsible for generating action potential in smooth muscle?

Answer 8

Calcium

Question 9

What is different about the length tension curve between skeletal and smooth muscle?

Answer 9

Smooth muscle can adjust its length tension curve in order to maintain closer to the ideal.

Question 10

histology:

Sk. M

Sm. M.

Answer 10

large, multi nucleated, striated cells

small, single nucleus, no striations

Question 11

Sarcoplasmic reticulum

Sk. M.

Sm. M.

Answer 11

Sk. M: large, well developed, SR with triads, well developed T tubules

Sm. M: poorly developed SR, T tubules, membrane with caveoli

Question 12

thin filaments

Sk. M

Sm. M

Answer 12

Sk. M actin, tropomyosin, tropinin

actin and tropomyosin

Question 13

Thin filament number

Sk. m

Sm. M

Answer 13

fewer thin filaments in skeletal muscle than in smooth muscle

Question 14

thick filaments

Sk. M

Sm. M

Answer 14

Sk. M. myosin, ATPase faster

Sm. M. myosin, ATPase slower, myosin light chain prominence

Question 15

thick filament number

Sk. M.

Sm. M

Answer 15

Sk. M greater than in Sm, M

Question 16

innervation

Sk. M

Sm. M

Answer 16

sk. M. a-motor neurons

Sm. M, multiple, intrinsic and autonomic nervous system

Question 17

NTMs

Sk. M

Sm.M

Answer 17

Sk. M-ach, excititory

Sm. M-Ach, epi, NE, excite or inhibit

Question 18

Transmission specialization

Sk. M

Sm. M

Answer 18

SK. M. NMJ

Sm. M. No NMJ, uses varicosties, no endplate specialization

Question 19

NTM receptors

Sk. M

Sm. M

Answer 19

SK. M nicotinic cholinergic

Sm. M. muscarinic cholinergic, adrenergic, others

Question 20

Other forms of activation

Sk. M

Sm. M

Answer 20

sk. M-none

Sm. M-blood borne, paracrine, intrinsic

Question 21

ACtion potential

Sk. M

Sm. M

Answer 21

Sk. M-required

Sm. M-No, pacemaker activity, hormonal

Question 22

Source of Ca

Sk. M

Sm. M

Answer 22

Sk. M-release from SR

Sm. M-release from SR and ECF influx

Question 23

role of calcium

Sk. M

Sm. M

Answer 23

Sk. M-binds to troponin

Sm. M-binds to calmodulin, activates MLCK

Question 24

Mechanism to alow actin and myosin binding

SK. M

Sm. M

Answer 24

Sk. M-tropomuposin moved by troponin

Sm. M-pi of myosin light chain

Question 25

Relaxation SK. M Sm. M

Answer 25

Sk. M-removal of Ca from troponin Sm. M-activation of light chain phosphatase, dephos.

Question 26

describe multi-unit smooth muscle

Answer 26

fibers operate individually, innervated by a single nerve ex: ciliary muscle of eye, iris, piloeretor muscle

Question 27

Describe unitary smooth muscle

Answer 27

visceral smooth muscle that works as a unit cell membranes adhere and contain gap junctions ex: GI, bile ducts, uterus

Question 28

In smooth muscle, what does actin attach to?

Answer 28

dense bodies/adherens junctions

Question 29

describe smooth muscle contraction

Answer 29

cycling of myosin cross bridges is slower than SK. M. the time myosin and actin are attached is greater which leads to a greater force while demanding less ATP

Question 30

Describe the latch mechanims

Answer 30

as excitation in the smooth muscle slows, contraction remains

Question 31

How does calcium enter the smooth muscle cell for contraction?

Answer 31

calcium enters cytosol via plasma membrane calcium channels release from SR is minor some comes in through ryanodine receptors or IP3 gates

Question 32

Most calcium enters the smooth muscle cell via

Answer 32

sarcolemma-K type voltage gated Ca channels and receptor activated ca channels

Question 33

CA leaves the cell via

Answer 33

SERCA 3Na/Ca antiporter sarcolemma Ca ATPase

Question 34

What does intracellular Ca bind to reversibly and what does that complex activate?

Answer 34

Ca binds reversible to calmodulin which activates MLCK which Pi the myosin head contraction strength is generally proportional to Ca levels Now actin and myosin can bind and contract the muscle

Question 35

What does myosin light chain phosphatase do?

Answer 35

removes Pi group from MLC and along with calcium pumps to remove calcium ushers in the relaxation state of the smooth muscle

Question 36

How does NE/Epi control SM. M?

Answer 36

adrenergic excitatory (contract) via A1 receptors inhibitory (relax) via B2 receptors

Question 37

How does Ach control SM. M?

Answer 37

PSN excitatory or inhibitory contraction is a direct effect while relaxation is an indirect effect

Question 38

How does angiotenin II, vasopressin and endothelin control smooth muscle? How does adenosine and NO control smooth muscle?

Answer 38

Contract! Relax!

Question 39

What are some environmental cues of smooth muscle control and their effect?

Answer 39

hypoxia excess Co2 increased H adenosine, LA, increased K, etc can call local dilation in vasculature sm.m.

Question 40

what are spike potentials? what are slow waves? What are plateaus?

Answer 40

stimulated by hormones, NTMs, stretch and spontaneously oscillating Ca influx and K efflux, have pacemaker capabilities stimualted by NTMs, stretch

Question 41

Describe the latch mechanism

Answer 41

it is a way to increase tension while decreasing ATP usage during Sm. M contraction light chain gets dephoshp. cycle proceeds slowly, and attached cross bridges are still generating tension (20-30%) overall-increases time of contraction