FORM AND FUNCTION (Smooth Muscle 1)

Question 1

Cardiac muscle:

Answer 1

-non-striated
-innervated by autonomic NS
-most diverse

Question 2

2 types of smooth muscle:

Answer 2

-multiunit
-single unit

Question 3

Multiunit:

Answer 3

-often single innervation for each
>not connected to each other (ex. similar to skeletal muscle)
-contraction is neurogenic
Ex. muscles in iris, walls of large arteries

Question 4

Single unit:

Answer 4

-contract together
>connected via gap junctions (ex. similar to cardiac muscle)
-contraction is myogenic
Ex. in walls of most viscera of the body

Question 5

Smooth muscle cell structure:

Answer 5

-elongated with tapered ends (“spindle-shaped”)
-smaller
-single nucleus, not striated
-dense bodies
-caveolae
-cell form sheets, not long fibers

Question 6

Dense bodies:

Answer 6

-analogous to Z-lines in striated muscles
-located on PM and cytoplasm
-held in place by cytoskeleton
-the cells ‘squeeze’ out of them during a contraction (wavy structure)

Question 7

Organization of different smooth muscle (3)

Answer 7

-surrounds arterioles
-small intestine: circular layer: mixes food and a longitudinal layer that moves the food along *perpendicular to each other)
-tiny projections: small testicular duct

Question 8

Relationship between MP and generation of force:

Answer 8

-variable ways to regulate force generation
-MP is not stable
>periodic oscillation of RMP sufficiently depolarized (-60 to -40mV)
-AP is highly variable

Question 9

AP in smooth muscle:

Answer 9

-highly variable
-not always need to initiate contraction
>certain agents (drugs) can increase intracellular Ca2+ (=force produced) without changing the MP =>pharmacomechanical coupling

Question 10

2 types of contraction:

Answer 10

1. Active contraction: phasic
2. Sustained contraction: tonic

Question 11

Active contraction: phasic

Answer 11

-alternating contractions and relaxations
Ex. peristalsis in digestive system, where smooth muscles layers rhythmically contact and relax to move substances

Question 12

Sustained contraction: tonic

Answer 12

-continuous, prolonged contractions
Ex. blood vessels maintaining specific tone to regulate blood flow and spincters

Question 13

Membrane system for excitation-contraction coupling:

Answer 13

1. Specialized membrane systems
2. Caveolae
3. Calcium sources

Question 14

Specialized membrane structures:

Answer 14

-less developed
-absence of T-tubules

Question 15

Caveolae:

Answer 15

-areas where sarcolemma invaginate
>don’t need t-tubules because the cells are so much smaller
-positioned close to the SR

Question 16

Calcium sources:

Answer 16

-from ECF through DHPR
-additional source from SR through RYR

Question 17

Excitation-contraction coupling in smooth muscles:

Answer 17

1. Filament anchoring and ratio
2. Calcium role
3. Myosin activation and regulation

Question 18

Filament anchoring and ratio:

Answer 18

-thin filaments anchor to dense bodies
-actin to myosin ratio 15:1, compared to 2:1 in skeletal muscles

Question 19

Calcium role:

Answer 19

-influx of Ca2+ ions activates the MLCK

Question 20

Myosin activation and regulation:

Answer 20

-myosin kinase
-myosin phosphatase