Contraction of Smooth Muscle

In what manner do smooth muscles contract

In a slow, synchronous fashion

What are pacemaker cells

Cells that, once excited, act as "drummers" to set the pace for contraction of the entire muscle sheet

Do pacemaker cells need a stimuli to depolarize

No, they depolarize spontaneously

How is contraction of smooth muscle similar to that of skeletal muscle

Both require a rise of intracellular calcium ions

Actin and myosin interact by sliding

ATP energizes the sliding process

How does calcium activate myosin in smooth muscle

Calcium interacts with calmodulin, which then interacts with myosin light chain kinase, or myosin kinase, which phosphorylates myosin and activates it

What causes smooth muscles to relax

When intercellular Ca2+ levels drop

Does smooth muscle take longer to contract and relax than skeletal muscles

Yes, about 30x longer

Is smooth or skeletal muscle contraction more efficient

Smooth

Is smooth msucle comparable to a speedy wind-up car or a locomotive engine that lumbers along tirelessly

The choo choo train

What is smooth muscle tone

A moderate degree of contraction maintained constantly without fatiguing.

How does smooth muscles get its ATP

Aerobic pathways

What can regulate smooth muscle contraction

Nerves, hormones or local chemicals.

What happens when acetylcholine binds to smooth muscles, say in the bronchioles

A strong contraction that narrows the bronchioles

What happens when norepinephrine binds to smooth muscle, say in the bronchioles

The muscle relaxes, which dilates the bronchioles

Can smooth muscle cells depolarize spontaneously

Yes, in some with no nerve supply they depolarize spontaneously or in response to chemical stimuli that bind to G protein-linked receptors

What are G protein-linked receptors

the on-off switch for signal transduction

What chemical factors can cause smooth muscles to contract without change in action potential

Certain hormones, histamines, excess carbon dioxide, low pH, lack of oxygen

What does the hormone gastrin stimulate

Stomach smooth muscle to contract so it can churn foodstuffs more efficiently