Smooth Muscle

Question 1

6 primary groups of smooth muscle in the body

Answer 1

vascular, GI, urinary, respiratory, reproductive, ocular

Question 2

smooth muscle can be categorized in 3 ways

Answer 2

location, contraction pattern, single vs multi unit

Question 3

tonic

Answer 3

continuously contracted (but can be variable)

Question 4

phasic

Answer 4

periodic contraction and relaxtion

Question 5

single unit smooth muscle cells

Answer 5

connected by gap junctions and the cell contracts as a single unit - most smooth muscle bc coordinated contraction (small intestines)

Question 6

multi-unit smooth muscle cells

Answer 6

not electrically linked, and each cell must be stimulated independently - the eye

Question 7

variscosities

Answer 7

although distinct motor end plates don’t exist, smooth muscle regulation by autonomic nerves - smooth muscles use less energy - sustains contraction for longer periods of time ex: bladder vs plank - work together

Question 8

smooth muscle organization

Answer 8

intermediate filaments and protein dense bodies form the cytoskeleton. actin attaches to the dense bodies each myosin molecule is surrounded by actin filaments. smooth muscle- dense bundles maintain sturcture - 10 actin to 15 myosin

actin more dense in skeletal muscle 2:4

Question 9

RMP in cardiac

Answer 9

-90 mV

Question 10

smooth muscle RMP

Answer 10

-80 to -40 mV due to leakiness of Na+/Ca+

Question 11

slow wave potentials

Answer 11

cyclic depolarization and repolarization allows for cyclic contraction of cells resulting in waves of peristalsis that sweep through the GI tract

Question 12

leak currents

Answer 12

mediated by Na + and Ca+ entering through the voltage independent non selective cation channel. upstroke of an action potential is from ca2+ entering the cell via VGCC

Question 13

electrochemical coupling

Answer 13

contraction caused by an electrical signals

Question 14

pharmacomechanical coupling

Answer 14

chemical signals change muscle tension through signal transduction pathways with little or no change membrane potential - NT, paracrine, stretch and various hormones may result in contractions of smooth muscle without first eliciting an action potential - most still require influx of Ca2+

Question 15

sources of intracellular ca2+

Answer 15

• Ca2+ increases due to entry through VGCC or from SR

there is some Ca induced Ca release and RyR but most from SR-released Ca from IP3 binding to IP3 receptors on SR

Question 16

biochemistry of SM contraction

Answer 16

1. intracellular Ca inc when Ca enters cell and released from SR
2. Ca binds to calmodulin (CaM)
3. Ca-CaM activates myosin like chain kinase (MLCK)
4. MLCK phosphorylates and activates light chains in myosin heads and increases myosin ATPase activity
5. active myosin cross bridges slide along actin and create muscle tension

(NT can elicit a contraction outside the cell)

Question 17

GPCR-phospholipase C transduction

Answer 17

1. signal molecule activates receptor and G protein
2. G protein activates phospholipase C (PLC) - amplifier enzyme
3. PLC converts membrane phospholipids into diacylglycerol (DAG) which remains in the membrane and IP3 which diffuses into the cytoplasm
4. DAG activates protein kinase C (PKC) which phosphorylates proteins
5. IP3 causes release of Ca2+ from organelles creating a Ca2+ signal

Question 18

effect of phosphorylation : MLCK

Answer 18

kinases groups of enzymes that add a phosphate to different proteins - myosin is phosphorylated by MLCK - increases myosin’s ability to interact with actin - when MLCK is phosphorylated it is inactivated!

Question 19

biochemistry of SM relaxation

Answer 19

1. free Ca in cytosol decreases when Ca is pumped out of the cell or back into the SR
2. Ca unbinds from CaM, MLCK activity dec
3. mysoin phosphatase removes phosphate from MLCK which dec myosin ATPase activity
4. less myosin ATPase activity results in dec muscle tension

most relax doesn’t happen this way

Question 20

inc cAMP in cardiac vs SM

Answer 20

elevation of cAMP in cardiac increase HR contraction
SM cAMP in relaxes - activates myosin phosphatase which causes phosphate to be removed from myosin light chains which dec myosin ATPase activity

Question 21

cAMP dependent relaxation of smooth muscle

Answer 21

activation of PKG - phosphorylation of MLCK - decreased phosphorylation of myosin