Smooth Muscle

Question 1

What are the characteristics of smooth muscles?

Answer 1

-specialized for slow, steady, long contractions

• contractions are slower to develop AND last significantly longer than both skeletal and cardiac muscle twitches
• primary oxidative metabolism

Question 2

What is cellular shape of smooth muscle?

Answer 2

elongated & tapered

Question 3

Are smooth muscle cells striated or non-striated?

Answer 3

non-striated

Question 4

Does smooth muscle have T-tubules?

Answer 4

No

Question 5

Contractile filaments of smooth muscle:

Answer 5

smooth myocytes contain actin & mysosin

Question 6

Are actin & myosin longer or shorter in smooth muscle?

Answer 6

Longer

Question 7

More or less myosin fibers than skeletal/cardiac myocytes?

Answer 7

LESS

Question 8

Alpha-actinin attaches to _______ _______ on the cell membrane

Answer 8

dense bodies

Question 9

Smooth muscle lacks ________

Answer 9

troponin

Question 10

Calcium binds to __________

Answer 10

Calmodulin

Question 11

Two actin-binding proteins:

Answer 11

1. Calponin
2. Caldesmon

Question 12

What does calponin do?

Answer 12

inhibits myosin ATPase

Question 13

What does caldesmon do?

Answer 13

inhibits myosin/actin bond

Question 14

T/F Smooth muscle can be a single-unit (gap junctions) or multi-unit (no gap junctions)

Answer 14

True

Question 15

Requirements for smooth muscle contraction:

Answer 15

Calcium & ATP

Question 16

Calcium binds to _______

Answer 16

calmondulin

Question 17

Calcium removes ________ & ________ from _______

Answer 17

• calponin
• caldesmon
• actin

Question 18

_______ ________ has an ATPase

Answer 18

Myosin head

Question 19

Contraction can be stimulated by:

Answer 19

1. Stretch
2. Ligands (NTs/hormones)
3. Intrinsic activity (pacemaker cells - contract their own)

Question 20

T/F: Action potentials are not necessarily required for increases in contractile force

Answer 20

True

Question 21

_________ potentials can open ________ channels which in turn can initiate calcium-induced Ca release from ________

Answer 21

• Graded
• Calcium
• SR

Question 22

Intracellular calcium binds to _________

Answer 22

calmodulin

Question 23

Many smooth muscle cells (ex: vascular) are ________ smooth muscle cells

Answer 23

tonic

• Normally contracted (have “tone”) but can alter their force of contraction
• Can contract/relax from resting

Question 24

In cross bridge cycling in smooth muscle, Ca binds to calmodulin for the activation of the ______ _______ _______ _______

Answer 24

myosin light chain kinase (MLCK)

Question 25

myosin light chain kinase (MLCK) phosphorylates the myosin light chanin so that ______ binds to ______

Answer 25

myosin binds to actin

Question 26

Myosin light chain will never enter into cross-bridge cycling unless it is _____________

Answer 26

phosphorylated

Question 27

Phosphorylated cross-bridges continue to cycle (myosin ATPase) is active) until __________ _________ dephosphorylates the ________ ________

Answer 27

- myosin phosphatase - myosin head ## Footnote Probably never get complete relaxation unless calcium is removed

Question 28

Ways to increase Ca within smooth muscle:

Answer 28

- depolarization by an action potential or a graded potential - Hormones or NTs can open Ca channel

Question 29

When the myosin head is __________, cross bridges repeatedly form & break if ________ IS present

Answer 29

- Phosphorylated - ATP

Question 30

Even when myosin is dephosphorylated, myosin and actin can form _______ _______

Answer 30

latch bridges

Question 31

In latch state, tension is maintained even though _______ & _______ are diminished

Answer 31

ATP & Ca

Question 32

In latch state, myosin heads stay bound to ________ ________ (and does NOT require ________)

Answer 32

- actin filaments - ATP

Question 33

Latch state allows for "_______ _______" sustained contraction at low cost

Answer 33

tonic contraction