Smooth Muscle

Question 0

Purpose of Smooth Muscle

Answer 0

1. shorten to provide motility
2. change shape of organ
3. maintain sustained contractions to maintain tone

Question 1

Location of Smooth Muscle

Answer 1

walls of hollow organs & tubes

Question 2

Ultrastructure of smooth muscle

Answer 2

Arterioles = circumfrential
Intestines = longitudinal on top & transverse on bottom
Testicular ducts = unique square shape

Question 3

Structural Properties of Smooth M.

Answer 3

nonstriated, spindle-shaped, single nucleus, involuntary

Question 4

Types of Electrical Coupling in Smooth M.

Answer 4

1. Multi-unit

2. Single unit

Question 5

Multi-unit electrical coupling

Answer 5

cells aren’t electrically linked & are independently stimulated

Question 6

Multi-unit electrical coupling allows

Answer 6

fine control of contraction

Question 7

Cells involved in multi-unit electrical coupling are

Answer 7

insulated from each other by collagen

Question 8

Examples of smooth muscle with multi-unit electrical coupling

Answer 8

iris, ciliary bodies, uterus (when pregnant)

Question 9

Single Unit Electrical Coupling

Answer 9

most common type

Question 10

How does single-unit electrical coupling work?

Answer 10

AP spreads through gap junction & there is one varicosity per multiple cells

Question 11

Single Unit Electrical Coupling contraction

Answer 11

cells contract simultaneously

Question 12

Examples of Single Unit Smooth M. Electrical Coupling

Answer 12

GI tract, urinary bladder, blood vessels, uterus (close to parturition)

Question 13

Smooth M. Contractile Behavior Classifications

Answer 13

1. Tonic Smooth M.

2. Phasic Smooth M.

Question 14

Tonic Smooth M.

Answer 14

normally contracted muscle that generates variable steady state force

Question 15

Tonic smooth muscle responds

Answer 15

to graded changed in Vm. It is proportional to Vm

Question 16

Phasic Smooth M. Characteristics

Answer 16

• rhythmic contractions (peristalsis)
• voluntary intermittent activity
• AP based

Question 17

Smooth M. Contractile Arrangements

Answer 17

Scaffold System of intermediate filaments & dense bodies

Question 18

intermediate filaments

Answer 18

• scaffold around smooth m. cells

- do NOT aid in contraction

Question 19

location of intermediate filaments

Answer 19

under membrane & surrounding nucleus

Question 20

dense bodies

Answer 20

anchor actin filaments

Question 21

actin traversing between cells

Answer 21

• actin enters dense body & leaves to interact with the next cell.
• helps surrounding cells contract too!

Question 22

Smooth M. contraction length

Answer 22

more interaction between actin & myosin filaments

Question 23

Smooth M. myosin filaments

Answer 23

• longer than skeletal m. myosin filaments
• hinged heads located along entire length
• “side-polar” cross-bridges

Question 24

Smooth m. myosin filaments allow

Answer 24

cells to contract to 80% of their length because of the scaffold vs 30% length contraction in skeletal m.

Question 25

Smooth M. Contraction depends on

Answer 25

MLCK/MLCP activity

Question 26

Smooth M. Contraction Mechanism

Answer 26

Ca influx (mostly from ECF) => Ca binds to Calmodulin => Ca-Calmodulin activates MLCK => MLCK phosphorylates MLC => Phosphorylated MLC activates myosin head allowing it to bind to actin => CONTRACTION

Question 27

MLCK stands for

Answer 27

myosin light chain kinase

Question 28

MLCK function

Answer 28

phosphorylation of MLC

Question 29

MLC =

Answer 29

myosin light chain

Question 30

MLCP

Answer 30

Myosin Light Chain Phophytase

Question 31

MLCP function

Answer 31

dephosphorylates myosin & decreases myosin/actin interaction

Question 32

MLCK:MLCP activity

Answer 32

determines level of smooth m. contraction

Question 33

Chemical Initiation of Smooth M. Contraction

Answer 33

1. Intrinsic activity of pacemaker cells for single unit 2. Neurotransmitters 3. Hormones 4. Pharmacological agents

Question 34

Intrinsic activity of pacemaker cells for single unit electrical coupling

Answer 34

stimulates AP in visceral smooth m.

Question 35

Neurotransmitters

Answer 35

1 varicosity/muscle cell in multi-unit | 1 varicosity/multiple cells in single unit & communicate via gap junctions

Question 36

Pharmacological Agents

Answer 36

delivered via vaculature

Question 37

What is ABSOLUTELY necessary for SMOOTH m. contraction?

Answer 37

CALCIUM

Question 38

Mechanism for Initiation of VISCERAL Smooth M. Contraction

Answer 38

Stimulated by APs

Question 39

Mechanisms for Initiation of VASCULAR smooth m. contraction

Answer 39

stimulated by slow wave potentials by graded changes in Vm AND stimulated by hormones and pharmacological agents

Question 40

Hormone & Pharmacological Agent Effect on Vascular Smooth M. cells

Answer 40

- no change in Vm | - still get contraction & relaxation

Question 41

Characteristics of Smooth M.

Answer 41

- slow contraction - slow relaxation - less ATP used to generate same force as skeletal m. - use only 25-30% myostin-actin cross-bridges to generate max. amount of tension

Question 42

Slow contraction of smooth m. permitted by

Answer 42

slow ATP splitting by myosin ATPase

Question 43

Slow relaxation of smooth m. provided by

Answer 43

slow Ca removal by Na/Ca exchangers

Question 44

Latch State

Answer 44

Smooth m. only using 25-30% of myosin:actin cross-bridges to generate max. amount of tension

Question 45

Tonic contraction

Answer 45

keeps some level of basal tone to get latch state because of continuous stimulation

Question 46

Tonic contraction force

Answer 46

maintained by low ATP utilization

Question 47

Tonic contraction works by

Answer 47

lowering Ca => dephosphorylation of MLC while in attached state (actin/myosin are slower to detach when MLC dephosphorylates)

Question 48

Relaxation of Smooth M. done by:

Answer 48

1st: Ca pumps 2nd: Ca ATPases.

Question 49

Smooth M. Ca ATPases

Answer 49

slower to act than those in striated muscle