smooth muscle

Question 1

location of smooth muscle

Answer 1

vascular, gastrointestinal, urinary, respiratory, reproductive, ocular; not very uniform (unlike skeletal muscle)

Question 2

Phasic smooth muscles

Answer 2

one and off alternate; no force for beginning tension

Question 3

tonic smooth muscles

Answer 3

always some level of contraction

Question 4

single-unit smooth muscle

Answer 4

electrical synapse: gap junction; amount of calcium that enters the cell determines the force of contraction

Question 5

multi-unit smooth muscle

Answer 5

individual chemical synapses w varicosities; increasing the force of contraction requires recruitment of additional fibers

Question 6

does smooth muscles have a shorter or wider range for optimal length and force generation?

Answer 6

wider range for optimal length and force generation

Question 7

impact of organs with multiple layers of smooth muscles

Answer 7

changes shape of organ

Question 8

consequence of less energy required for maintenance of tension

Answer 8

prolonged contractions; has ability to slow down myosin ATPase so that cross bridges cycle slowly as they maintain force

Question 9

shape of smooth muscles

Answer 9

small spindle-shaped with a single nucleus; not arranged in sarcomeres; lacks distinct banding patterns

Question 10

contraction can be caused by

Answer 10

electromechanical coupling, pharmacomechanical coupling, myogenic stimulation or contraction

Question 11

electromechanical coupling

Answer 11

changes in membrane potential; electrical signals; use of AP to stimulate smooth muscle

Question 12

pharmacomechanical coupling

Answer 12

minimal changes in membrane potentials; chemical signals

Question 13

myogenic stimulation or contraction

Answer 13

originates in smooth muscle; mechanical signals like muscle cell stretch

Question 14

parasympathetic control of smooth muscle

Answer 14

sphincter of iris

Question 15

sympathetic control of smooth muscles

Answer 15

radial muscle of iris

Question 16

smooth muscle structure

Answer 16

more actin; has tropomyosin but lacks troponin; less myosin which are surrounded by actin filaments are are arranged so that each myosin molecule is in the center of a bundle of actin molecules; run parallel to long axis of cell; longer myosin filaments, fully covered by myosin head which enables smooth muscle to stretch more; actin anchored to dense bodies; dense bodies anchored to cell membrane; individual cells anchored together

Question 17

Sarcoplasmic reticulum

Answer 17

less developed so not as much calcium stored; still associated w cell membrane

Question 18

Invaginations

Answer 18

caveolae; participate in cell signaling; close association w SR

Question 19

latch state

Answer 19

dephosphorylated myosin can remain in isometric contraction; significant factor in the ability of smooth muscle to sustain contraction without fatiguing

Question 20

MCLK > MLCP

Answer 20

contraction

Question 21

MLCK < MLCP

Answer 21

relaxation

Question 22

2 sources of calcium in smooth muscle

Answer 22

ECF and SR

Question 23

slow wave potentials

Answer 23

regular rhythm of changing membrane potential and it does not usually reach threshold; you have to have an additional stimulus to bump you up to threshold. **cells exhibit cyclic depolarization and repolarization of their membrane potential

Question 24

pacemaker potentials

Answer 24

regular depolarizations that always reach threshold and fire an AP; generate regular rhythms of contractions; self-stimulating; slow wave and pacemaker potentials are due to ion channels in the cell membrane that spontaneously open and close

Question 25

alpha adrenergic receptors and epinephrine

Answer 25

Smooth muscle contraction

Question 26

beta2 adrenergic receptors and epinephrine

Answer 26

smooth muscle relaxation

Question 27

paracrine agents

Answer 27

histamistime released in immune response (asthma –> constriction); nitric oxide released by endothelial cells (vasodilator)