Smooth Muscle

Question 1

What are gap junctions’ roles in smooth muscle?

Answer 1

couple smooth muscle cells so the AP can spread

Question 2

What do pacemaker cells do to contribute to contraction of smooth muscle?

Answer 2

induce spontaneous action potential, which can be spread to other nonpacemaker cells

Question 3

in smooth muscle, calcium binds to what?

Answer 3

calmodulin

Question 4

what does activated calmodulin do?

Answer 4

activates myosin light chain kinase enzymes

Question 5

What most directly triggers release of calcium from SR of smooth muscle cells?

Answer 5

calcium influx into sarcoplasm

Question 6

why doesn’t cross bridge require as much ATP as skeletal muscle?

Answer 6

myosin and actin “latch” to one another more strongly

Question 7

Actin is anchored to Z-discs in skeletal muscle. What is actin anchored to in smooth muscle?

Answer 7

dense bodies, which are also anchored to intermediate filaments

Question 8

How are myosin and actin arranged differently in smooth muscle?

Answer 8

Myosin heads are not on multiple sides except in the middle, because actin is not on all sides of thin filaments

Question 9

describe actin, dense bodies, and intermediate filaments in one contracted smooth muscle cell

Answer 9

actin pulls on dense bodies, and dense bodies pull on intermediate filament network, which shortens the cell like a corkscrew

Question 10

Why are MLCK sluggish?

Answer 10

have to remove phosphate from ATP to put it on myosin head groups

Question 11

What steps are involved in relaxing smooth muscle? Use the words calcium, SR, and dephosphorylation

Answer 11

Calcium detaches from calmodulin
Active transport of calcium into SR and back out of cell
Dephosphorylation of myosin to inactive myosin

Question 12

Discuss why the same neurotransmitter could have different effects on different smooth muscles

Answer 12

Different muscles have different NT receptors, so the same NT could cause contraction or relaxation depending on the receptor it binds to

Question 13

Discuss how g-protein coupled receptors affect contraction of smooth muscle in the stomach

Answer 13

gastrin released by g-cells in stretched stomach after eating binds to g-protein coupled receptors, which stimulates higher force and rate of stomach’s smooth muscle

Question 14

Name two special features of smooth muscle

Answer 14

1) Response to stretch - automatically contracts when stretched, but quickly adapts to new length and relaxes, contracts on demand even when very stretched
2) Length and tension changes - can contract when between half and twice its resting length because of the myofilament arrangement

Basically, it handles stretch a lot better than skeletal muscle

Question 15

Name the two types of smooth muscle and state which one is more common

Answer 15

Multi-unit smooth muscle (only large airways and arteries, arrector pili, and internal eye)
Single-unit (unitary) smooth muscle (a lot more common)

Question 16

What does multi-unit smooth muscle have instead of gap junctions? Why?

Answer 16

cytoplasms aren’t connected, so it needs more innervation, so it has varicosities between all cells