Phys 10-11: Smooth Muscle

Front 1

describe the contractile structure of smooth muslce

Back 1

no striations or sarcomeres, actin and myosin are present, dense bodies anchor filaments (like a z line)

Front 2

compare smooth and skeletal muscle in terms of thin to thick filament ratio

Back 2

smooth muslce has a much higher thin to thick ration than both skeletal and cardiac (striated)

Front 3

T/F smooth muslce thin filaments have troponin and tropomyosin to regulate contraction

Back 3

false, smooth muslce thin filaments are not associated with these proteins. Smooth muscle contraction is regulated by Calmodulin+MLCK activity

Front 4

How are cross bridges activated and terminated in smooth muslce

Back 4

MLCK activates cross bridges by phosphorylating myosin allowing it to attach to actin, Myosin phosphoryalse removes the phosphate and stops cross bridge cycling

Front 5

how does the resting membrane potential smooth muscle compare to that of skeletal muscle

Back 5

Much less negative becasue much lower gK

Front 6

describe the concept o fpharmacomechanical coupling in smoth muscle

Back 6

change in force with no change in membrane potential, there is an increase in contractile filament Ca sensitiviy with IP3 induced Ca released

Front 7

How does the source of Ca in smooth muscle differ from that in skeletal muscle

Back 7

1. Majory of Ca is from extracellular fluid 2. SR is less extensive an release is via PLC-IP3 mechanism rather than ryanodien receptor, note Ca induced Ca release as well

Front 8

How are Ca ions removed from smooth muscle cytoplasm

Back 8

Plasma membrane ATPase (PMCA), SERCA, Na:Ca exchange (maybe, more important in cardiac)

Front 9

compare and constrast the velocity of contraction in smooth and skeletal muscle

Back 9

smooth muscle is mucher slower and more variable than skeletal

Front 10

Compare smooth and skeletal muslce in terms of force per cross sectional area

Back 10

smooth muscle can generate more force per cross sectinonal area

Front 11

compare the frequency of cross bridge cycling in smooth and skeletal muscle

Back 11

skeletal cross bridges cycle much faster than smooth, note smooth muscle latch mechanism

Front 12

how do single and multi unit smooth msucles differ in ters of structure and function

Back 12

multi unit-descrete, separate fibers thtat operate independently and each innervated by a single nerve ending, thick basement membrane helps to separate cells; single unit-many fibers contract together, act as a syncytium, cell membranes joined by gap junctions

Front 13

describe the concept of strech induced relaxtion of smooth muslce

Back 13

ability to return to nearly original force of contraction after it has been elongated or shortened, important for visceral single unit muscle around hollow organs

Front 14

How does calcium activate smooth muscle

Back 14

Calcium inos bind with calmodulin, the complex activates myosin light chain kinase, MLCK phosphorylates a light chain on the myosin head, the myosin head can now bind actin

Front 15

What happens to smooth muscle contraction when the calcium ion concentration falls

Back 15

MLCK becomes inactivated so no new myosin heads are phosphorylated. Additinally, myosin phosphatas removes P from the myosin heads and prevents them from bindng to actin

Front 16

the time required for relaxation of smooth muscle contraction is determined mostly by

Back 16

the amount of active myosin phosphatase in a cell

Front 17

What is the mechanism behind the latch phenomenon in smooth muscle

Back 17

MLCK and myosin phosphatase decrease in activity allowing the myosin heads to remain attached to the actin filament for a longer portion of the cycling peroid. (note it is the number of heads attached to actin that determines the static force of contraction). The tension is maintained but little energy is used because ATP is not being degraded except when a head detaches

Front 18

How do smooth and skeletal muscle differ in terms of methods of stimulation

Back 18

skeletal is stimulated by the nervous system exclusivley, smooth can be nerous, hormonal, strech, etc

Front 19

How does the NMJ differ in skeletal and smooth muscle

Back 19

in skeletal muscle, the NMJ is highly structured, in smooth, the autonomic nerve fibers branch diffusely on top of a sheet of muscle fibers and do not necesasrily make direct contact but rather secrete their transmitter into the matrix

Front 20

How do the axons that stimulate smooth muscle differ strucutrally from those that stimulate skeletal

Back 20

Skeletal muscle axons have branching feet at the motor end plate, smooth msucle axons have multiple varicosities distributed along the. Note also that while skeletal axons always release Ach, smooth contain Ach, and norepinephrine

Front 21

Acetylcholine and NE elicit different responses in different types of tissues. What determines whether the response is inhibitory or excitatory

Back 21

The type of receptor on the smooth muslce determines the type of responses and the efficacy of the NT

Front 22

AP with plateaus are a unique feature of single unit smooth muslce. What is the significance of these plateaus

Back 22

The repolarization of the membrane after the initial spike is delayed which allows for prolonged contraction. These plateaus occur becasuse the Ca channels responsible for depolarizng the membrane open slower and stay open longer than their Na counterparts in skeletal muscles

Front 23

Which ion is more important in generation a contraction is smooth muslce, sodium or calcium

Back 23

Calcium. Smooth muscle has fewer Na cahhenls and more Ca channels than skeletal muscle. The flow of Ca ions into the muscle is mainly responsible for generation of the action potential. Note however that the Ca channels open slower and remain open longer which occurs for the prolonged plateau of smooth muscle fibers, the Ca pumps that remove the Ca are also slower than those in skeletal

Front 24

How does strech elicit an AP in visceral (single unit) smooth muscle

Back 24

The AP results from a combination of the normal slow wave potentias and a decrease in the overal negativity of the membrane caused by the strech itself.

Front 25

T/F multi unit smooth muscle requires an aciton potential to contract

Back 25

false, multi unit smooth muscles do not usually generate action potentials because the fibers are too small. Rather the local depolarization caused by the neurotransmiter spreads electrotonically over the entire fiber and causes contraciton (since the muscle is small, a self propagating AP is not required)

Front 26

In general, how do hormones regulate smooth muslce contraction

Back 26

bind to hormone gated receptors; excitatory-hormone receptors open Na or Ca channels and depolarize them membrane; inhibitory- hormone closes Na/Ca channels or opens K channels and hyperpolarizes the cell, may also induce internal changes

Front 27

What would be the effect of a decrease in extracellular calcium ion concentration on smooth muscle contraction

Back 27

decreases, smooth muscle is dependent on extracellular Ca for contraction