Smooth M. DSA and Lecture

Question 1

what helps insulate the fibers from one another?

Answer 1

collagen and glycoprotein

Question 2

what are examples of multi-unit smooth m?

Answer 2

ciliary eye muscles, iris muscles, piloerector muscles

PIC

Question 3

what are unitary (synctial) smooth m. joined by?

Answer 3

gap junctions

Question 4

examples of unitary smooth m?

Answer 4

walls of viscera of the body, GI tract, bile ducts, ureters, uterus, blood vessels

Question 5

what is the structure of smooth m? ie how is actin attached?

Answer 5

actin attached to dense bodies, bonded together by intracellular protein bridges where contraction takes place

Question 6

the dense bodies in smooth m. serve the same role as what in skeletal m.?

Answer 6

Z discs

Question 7

what allows a hollow organ to maintain the same amount of pressure inside the lumen despite changes in volume?

Answer 7

stress-relaxation

Question 8

outline the steps in smooth m. contraction

Answer 8

1. Ca enters cell
2. Ca binds reversibly w/Calmodulin
3. Ca-Cam complex activates MLCK
4. Regulatory chain gets PO4’ed, head binds w/actin and m. contraction occurs

Question 9

what is the source of Ca ions in smooth m. contraction?

Answer 9

ECF (10^-3 M)

Question 10

what is the the time it takes for diffusion (200-300 ms) to occur called?

Answer 10

latent period

Question 11

how is an AP propagated?

Answer 11

AP –> caveolae –> Ca released from SR tubule

Question 12

TRUE or FALSE:

The more SR, the faster the m. contraction?

Answer 12

TRUE

Question 13

what is required for smooth m. relaxation?

Answer 13

ATP, calcium pump that pumps Ca ions out of smooth m. fiber back into ECF

Question 14

which lasts longer: skeletal m. contraction or smooth m.?

Answer 14

smooth m.

Question 15

what enzyme causes detachment of the myosin head from the actin filament and relaxation of the smooth m.?

Answer 15

myosin phosphatase (splits PO4 from the regulatory light chain)

Question 16

what do short smooth m. contractions depend on?

long?

Answer 16

SR

ECF Ca2+

Question 17

what does smooth m. of the guy, vasculature and respiratory tract do?

Answer 17

be energy efficient
maintain shape of organ
generate active tension when stretched
use little ATP
contract periodically to mix contents of organ

Question 18

where is smooth m. found?

Answer 18

vasculature
GI
urogenital tract
respiratory tract
eye

GRUVE

Question 19

what does intrinsic innervation of smooth m.?

Answer 19

gut, trachea, neurons

Independent of CNS + PNS

Question 20

what controls extrinsic innervation?

Answer 20

ANS

Question 21

what nts control smooth m. contraction?

what are their affects?

Answer 21

ACh excites gut sm
NorEpi/Epi inhibits gut sm, contraction of vascular sm
NO inhibits smooth m.

Question 22

can smooth m. be directly inhibited?

Answer 22

YES, has no motor end plate

Question 23

where are nts released in smooth m.?

Answer 23

varicosities

Question 24

what types of receptors does smooth m. have?

Answer 24

Muscarinic cholinergic

adrenergic (alpha + beta)

Question 25

what hormones may elicit smooth m. contraction?

Answer 25

Epi | CCK

Question 26

what paracrine molecule can activate smooth m.?

Answer 26

NO

Question 27

what is an alternate mechanism by which smooth m. may be activated?

Answer 27

stretch (ie. in vasculature)

Question 28

outline the steps in the LATCH mechanism

Answer 28

1. dephosphorylation of light chain (MLCK) 2. cycle proceeds VERY slowly 3. attached crossbridges still generating tension 4. way of INC tension and DEC ATP use

Question 29

as smooth m. is stretched, the myosin heads are free from the actin and allowed to interact with different thin filaments, what does this cause?

Answer 29

1. Reduces passive tension by reducing the strain on points of attachment to the membrane 2. allows smooth m. cell to continue to generate active tension over a wide range of length bc actin is always available for the myosin head

Question 30

What is multi-unit smooth m. composed of?

Answer 30

many separate smooth m. fibers