- 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

- Fewer myosin fibers than skeletal/cardiac myocytes - Myosin Filaments interspersed with actin

Cardio 2: Smooth Muscle Flashcards by sophie rosen

Main populations surround

“hollow organs”:

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

How well did you know this?

Not at all

Perfectly

Also important in (2)

ocular function, piloerection

How well did you know this?

Not at all

Perfectly

SM Contraction may cause (2)

propulsion or resistance

How well did you know this?

Not at all

Perfectly

Stimulus for contraction may be

intrinsic

How well did you know this?

Not at all

Perfectly

“Involuntary”: regulated by

efferent autonomic neurons, hormones,

and autocrine/paracrine signals

How well did you know this?

Not at all

Perfectly

SM cell size

Smaller cells with single central nucleus

How well did you know this?

Not at all

Perfectly

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

slow, steady, long

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

SM cell shape

elongated &

tapered

How well did you know this?

Not at all

Perfectly

SM striation

Smooth muscle is non-striated (

How well did you know this?

Not at all

Perfectly

Smooth muscle lacks —

and only has rudimentary

T-tubules

How well did you know this?

Not at all

Perfectly

Types of Smooth Muscle (2)

multi unit
single unit (unitary visceral)

How well did you know this?

Not at all

Perfectly

Multi-unit (6)

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

How well did you know this?

Not at all

Perfectly

Single-Unit (Unitary, Visceral) (6)

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

How well did you know this?

Not at all

Perfectly

Smooth myocytes contain (2)

actin & myosin

How well did you know this?

Not at all

Perfectly

Actin (3)

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

How well did you know this?

Not at all

Perfectly

Myosin (2)

Fewer myosin fibers than skeletal/cardiac myocytes

- Myosin Filaments interspersed with actin

How well did you know this?

Not at all

Perfectly

Smooth myocytes lack —

troponin

How well did you know this?

Not at all

Perfectly

Calcium binds to —

Calmodulin

How well did you know this?

Not at all

Perfectly

Two actin-binding proteins: (2)

a. Calponin inhibits myosin ATPase

b. Caldesmon inhibits myosin/actin bond

How well did you know this?

Not at all

Perfectly

Contraction results in — — of cell

rounding up

May contract efficiently over a wide

range of

resting lengths

Requirements for contraction: (3)

Calcium (*Extracellular/Some Intracellular)
ATP for contraction (myosin head has an ATPase)
Myosin Light Chain Phosphorylation

Calcium (*Extracellular/Some Intracellular) (2)

 Binds to calmodulin for contraction

Removes calponin & caldesmon from actin

3. Myosin Light Chain Phosphorylation (3)

 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

Smooth muscle contraction can be stimulated by (3)

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

Action potentials are not necessarily required for --- in contractile force

increases

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

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

Cross-Bridge Activation: (5)

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)

Two sources of Ca2+ : (2)

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

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

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

``` Cross Bridge Cycling in Smooth Muscle (2) ```

``` 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. ```

When myosin is dephosphorylated, myosin and actin may form

latch-bridges

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

decreases | decreases

``` When myosin is phosphorylated, cross bridges repeatedly form & break if --- is present ```

ATP

Latch State —

sustained contraction at low cost. | Tonic contractions creating smooth muscle tone.

Several mechanisms influencing

smooth muscle cell activation

Input to smooth muscle can be either

excitatory or inhibitory.

inputs influencing smooth muscle contractile activity (5)

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

Smooth Muscle Activation: Autonomic Motor Neurons | Do not form ---

synapses

Smooth Muscle Activation: Autonomic Motor Neurons | Axons have ---

Varicosities

Smooth Muscle Activation: Autonomic Motor Neurons | NT released into

interstitial | fluid

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

simple diffusion.

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

varicosity

Smooth Muscle Activation: Autonomic Motor Neurons | (2) contraction

Stimulate or inhibit

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

Vm | Activate or inhibit

Local factors, including (5), can also | alter smooth muscle tension.

``` paracrine signals, acidity, O2 and CO2 levels, osmolarity, and the ion composition of the extracellular fluid ```

Responses to local factors provide a means for

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

Many of these local factors induce

smooth muscle relaxation (ex. Nitric | oxide (NO)).

Some smooth muscles can also respond by contracting when they are

stretched

Stretching opens

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

Pacemaker Potentials (4)

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