10. Characteristics of smooth muscle

Question 1

General: what are the 2 major parts of the smooth muscle

Answer 1

single-unit smooth muscle
o Multi-unit smooth muscle

Question 2

General: Single-unit is found

Answer 2

Single unit smooth muscle is found in the walls of the body’s hollow and tubular organs

Question 3

General: single-unit: what does it do

Answer 3

Sustained contraction of the smooth muscle in
walls transfers pressure to the content or the organ, while alternating contractions and relaxations lead to mixing of the content.
o Can also create waves of contraction = peristaltic movements

Question 4

General: Multi-unit: found in

Answer 4

Multi-unit smooth muscle is primarily located in the eyes and skin

Question 5

General: multi-unit: responsible for:

Answer 5

Adjusting the diameter of the pupils according to the intensity of light
▪ Altering the curvature of the lens in the eye
▪ Changing the angle of hairs relative to skin
surface

Question 6

Structure: what does it contain

Answer 6

Contain both actin and myosin filaments, but they are not organized in sarcomers.

Question 7

Structure: actin filament

Answer 7

the actin filaments are attached to dense protein lattices, which are analogous to the Z-discs in skeletal muscle fibers.

Question 8

Structure:myosin filaments where are they

Answer 8

Myosin filaments are located between the actin filaments.

Question 9

Structure: myofilament bundles end

Answer 9

The ends on the myofilaments bundles
are attached to dense protein plates in the cell membrane.

Question 10

Structure: intermediate filaments what do they do

Answer 10

These filaments do not participate in the
contraction, but are a part of the cytoskeleton
that determined the shape of the cell.

Question 11

Contraction of smooth muscles: step 1

Answer 11

Stimulation of the cells result in increased calcium
concentration in the cytosol, due both to calcium influx through ion channels in the cell membrane, and to calcium release from the sarcoplasmic reticulum.

Question 12

Contraction of smooth muscles: step 2

Answer 12

Calcium binds to calmodulin

Question 13

Contraction of smooth muscles: step 3

Answer 13

Calcium-calmodulin complex activates myosin kinase.

Question 14

Contraction of smooth muscles: step 4

Answer 14

The activated myosin kinase transfers a phosphate group from ATP to the myosin heads.

Question 15

Contraction of smooth muscles: step 5

Answer 15

Phosphorylated myosin heads hydrolyze ATP and bind to actin.

Question 16

Contraction of smooth muscle: step 6

Answer 16

Cross-bridges are formed and broken as long as the myosin heads are phosphorylated, causing the cell to contract.

Question 17

Contraction of smooth muscle: step 7

Answer 17

When stimulation of the cell ceases, calcium pumps in the cell membrane and in the membrane of the sarcoplasmic reticulum will remove more calcium from the cytosol than flows in.

Question 18

Contraction of smooth muscle: step 8

Answer 18

The calcium concentration in the cytosol falls and calcium dissociates from calmodulin, and the activation of myosin kinase ceases.

Question 19

Contraction of smooth muscle: step 9

Answer 19

Myosin phosphatase dephosphorylates the myosin heads, which then lose their ATPase activity and the ability to bind to actin.

Question 20

Signals for smooth muscle contraction/relaxation: Relaxation of smooth muscle cells =

Answer 20

Relaxation of smooth muscle cells = vasodilation

Question 21

Signals for smooth muscle contraction/relaxation:Extension (stretching) of certain smooth muscle cells results in contraction

Answer 21

Bayliss effect