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Physiology > Cardio 2: Smooth Muscle > Flashcards

Cardio 2: Smooth Muscle Flashcards

1
Q

SM

Main populations surround

A

“hollow organs”:

blood vessels, airways, GI tract, uterus and Fallopian tubes, ureters and bladder

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2
Q

SM

Also important in (2)

A

ocular function, piloerection

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3
Q

SM Contraction may cause (2)

A

propulsion or resistance

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4
Q

SM

Stimulus for contraction may be

A

intrinsic

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5
Q

SM

“Involuntary”: regulated by

A

efferent autonomic neurons, hormones,

and autocrine/paracrine signals

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6
Q

SM cell size

A

Smaller cells with single central nucleus

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7
Q

SM Specialized for (3) contractions (compared to skeletal muscle)

A

slow, steady, long

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8
Q

Specialized for slow, steady, long contractions (compared to skeletal muscle) (4)

A
  1. Contractions are slower to develop (1/10 to 1/300 speed)
  2. Contractions last significantly longer (30x longer)
  3. Maximum force generation greater (up to 2x greater/cm2)
  4. Primarily oxidative metabolism
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9
Q

SM cell shape

A

elongated &

tapered

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10
Q

SM striation

A

Smooth muscle is non-striated (

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11
Q

Smooth muscle lacks —

and only has rudimentary

A

T-tubules

SR

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12
Q

Types of Smooth Muscle (2)

A 
multi unit
single unit (unitary visceral)
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13
Q

Multi-unit (6)

A 
No Gap Junctions
Each cell responds independently
Muscle behaves as multiple units
Control exerted mainly by nerve 
signals 
 Cells function independently
 No tone
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14
Q

Single-Unit (Unitary, Visceral) (6)

A 
 Cells connected by gap junctions
 Functional Syncytium
 Control by variety of stimuli
 Pacemaker cells
 Cells organizes into sheets or 
bundles
 May have tone
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15
Q

Smooth myocytes contain (2)

A

actin & myosin

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16
Q

Actin (3)

A
  • Higher levels and longer than in skeletal/cardiac myocytes
  • Alpha actinin attaches actin to dense bodies (Intracellular and
    Membrane bound)
  • Arranged diagonally to long axis of cell
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17
Q

Myosin (2)

A
  • Fewer myosin fibers than skeletal/cardiac myocytes

- Myosin Filaments interspersed with actin

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18
Q

Smooth myocytes lack —

A

troponin

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19
Q

Calcium binds to —

A

Calmodulin

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20
Q

Two actin-binding proteins: (2)

A

a. Calponin inhibits myosin ATPase

b. Caldesmon inhibits myosin/actin bond

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21
Q

Contraction results in — — of cell

A

rounding up

22
Q

May contract efficiently over a wide

range of

A

resting lengths

23
Q

Requirements for contraction: (3)

A
  1. Calcium (*Extracellular/Some Intracellular)
  2. ATP for contraction (myosin head has an ATPase)
  3. Myosin Light Chain Phosphorylation
24
Q
  1. Calcium (*Extracellular/Some Intracellular) (2)
A

 Binds to calmodulin for contraction

Removes calponin & caldesmon from actin

25
Q
  1. Myosin Light Chain Phosphorylation (3)
A

 Required for myosin head to interact with Actin
 Myosin light chain kinase – adds phosphate and begins contraction
 Myosin light chain phosphatase – removes phosphate and stops contraction

26
Q

Smooth muscle contraction can be stimulated by (3)

A
  1. Stretch
  2. Ligands (neurotransmitters/hormones/paracrines/autocrines)
  3. Intrinsic activity (pacemaker cells)
27
Q

Action potentials are not necessarily required for — in contractile force

A

increases

28
Q

Many smooth muscle cells (ex: vascular) are — smooth muscle cells.

A

tonic

They are normally contracted (have “tone”), but can alter their force of contraction.

29
Q

Cross-Bridge Activation: (5)

A

Cross-bridge cycling in smooth muscle is controlled by a Ca2+ regulated enzyme that phosphorylates myosin.
Only the phosphorylated form of smooth muscle myosin can bind to actin and undergo cross-bridge cycling.
This is done by myosin light chain kinase (MLCK).
 To relax a contracted smooth muscle, myosin must be dephosphorylated because dephosphorylated myosin is unable to bind to actin.
Dephosphorylation is mediated by the enzyme myosin light-chain phosphatase (MLCP)

30
Q

Two sources of Ca2+ : (2)

A 
1. The sarcoplasmic 
reticulum.
2. Extracellular Ca2+ 
entering the cell through 
plasma-membrane Ca2+ 
channels.
31
Q

To relax, the Ca2+ has to be removed: (2)

A

To SR via Ca++ ATPase

To ECF via Ca++ ATPase and Na+/Ca++ Exchanger

32
Q 
Cross Bridge Cycling in              
Smooth Muscle (2)
A 
A.Attachment of myosin to actin 
depends on the 
phosphorylation of the myosin 
by myosin light chain kinase 
(MLCK;  activated by calcium- 
calmodulin)
B. Phosphorylated cross-bridges 
continue to cycle (myosin 
ATPase is active) until myosin 
phosphatase 
dephosphorylates the myosin 
head.  Probably never get 
complete relaxation unless 
remove calcium.
33
Q

When myosin is
dephosphorylated, myosin and
actin may form

A

latch-bridges

34
Q

Tension is maintained although
Ca++ levels in cytosol — and ATP
usage —

A

decreases

decreases

35
Q 
When myosin is 
phosphorylated, cross 
bridges repeatedly form 
& break if --- is 
present
A

ATP

36
Q

Latch State —

A

sustained contraction at low cost.

Tonic contractions creating smooth muscle tone.

37
Q

Several mechanisms influencing

A

smooth muscle cell activation

38
Q

Input to smooth muscle can be either

A

excitatory or inhibitory.

39
Q

inputs influencing smooth muscle contractile activity (5)

A

spontaneous electrical activity in the PM of the muscle cell
NT released by autonomic neurons
hormones
locally induced changes in the chemical composition (paracrine factors, acidity, oxygen, osmolarity, and ion concentrations) of the extracellular fluid surrounding the cell
stretch

40
Q

Smooth Muscle Activation: Autonomic Motor Neurons

Do not form —

A

synapses

41
Q

Smooth Muscle Activation: Autonomic Motor Neurons

Axons have —

A

Varicosities

42
Q

Smooth Muscle Activation: Autonomic Motor Neurons

NT released into

A

interstitial

fluid

43
Q

Smooth Muscle Activation: Autonomic Motor Neurons
Distribute to receptors on
smooth muscle cell surface
via

A

simple diffusion.

44
Q

Smooth Muscle Activation: Autonomic Motor Neurons
Each smooth muscle cell
may be influenced by more
than one

A

varicosity

45
Q

Smooth Muscle Activation: Autonomic Motor Neurons

(2) contraction

A

Stimulate or inhibit

46
Q

Depending on Receptor
 May or may not induce – change
 (2) contraction

A

Vm

Activate or inhibit

47
Q

Local factors, including (5), can also

alter smooth muscle tension.

A 
paracrine signals, 
acidity, 
O2 and CO2 levels, 
osmolarity, and 
the ion composition of the extracellular fluid
48
Q

Responses to local factors provide a means for

A

altering smooth muscle
contraction in response to changes in the muscle’s immediate internal
environment, independent of long-distance signals from nerves and
hormones.

49
Q

Many of these local factors induce

A

smooth muscle relaxation (ex. Nitric

oxide (NO)).

50
Q

Some smooth muscles can also respond by contracting when they are

A

stretched

51
Q

Stretching opens

A

mechanosensitive ion channels, leading to
membrane depolarization. The resulting contraction opposes the forces
acting to stretch the muscle.

52
Q

Pacemaker Potentials (4)

A 
Pacemaker smooth muscle cells
Resting membrane not stable, 
slow depolarization to threshold
Mechanism unknown
Pacemaker Cells found in GI Tract 
(contract rhythmically without 
input)

Physiology (53 decks)

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