L12 Smooth Muscle Flashcards
The walls of hollow organs have what kind of muscle/.
Smooth muscle
How many nuclei does a smooth muscle cell have
ONE
Does smooth muscle have t-tubules?
No
What kind of muscle does these:
Produces motility
Maintains pressure
Regulates internal flow
Smooth msycle
Does smooth muscle have sarcomeres?
No, it is NOT striated
Where is the sarcoplasmic reticulum in smooth muscle?
In contact with the plasma membrane
How does calcium flow from one cell to the next in smooth muscle units?
Through connexons
Does smooth muscle have neuromuscular junctions?
NO!!!!!!!!!!
Smooth muscles are innervated by the autonomic nervous system
If smooth muscles don’t have neuromuscular junctions, what do we call the part where neurotransmitters are released onto the muscle?
Varicosities
Does smooth muscle have motor end plates?
NO!!
Do you need a lot of neurons innervating single-unit (myogenic) smooth muscle?
NO, because they have gap junctions, so the signal will flow through all the cells from a few small spots
What is another word for single-unit smooth muscle
Myogenic (because they have pacemakers and can originate their own signals sort of)
What is another name for multi unit smooth muscle?
Neurogenic
because the signal is originating in the nervous system
Why are multiunit muscles innervated so densely and so isolated
It allows for finer motor control
What kind of smooth muscle (myogenic or neurogenic) is in the eye, skin hair follicles, large blood vessels, small airways and vas deferen?
Neurogenic (multiunit)
What kind of smooth muscle (neurogenic or myogenic) is in thre GI tract, bladder, small blood vessels, uterus and ureter?
Myogenic (single unit)
Which has longer myosin filaments: smooth or skeletal muscle
Smooth muscle
Does smooth muscle contain troponin?
NO
What do actin filaments attach to in smooth muscle (it’s not Z disks because there are no sarcomeres)
Dense bodies
Instead of bands that contract, what is the arrangement of the dense bodies and filaments in smooth muslce?
Diamond shaped lattice
Where is contraction of smooth muslce regulated?
At the thick (myosin) filament
What increases the affinity of the myosin head for actin in smooth muscled?
A PHOSPHATE binding to the myosin
What happens to the calcium in smooth muscle when it is released from the SR?
It binds to calmodulin
What does calmodulin do?
Once calmodulin binds 4 calciums, it goes and turns on myosin light chain kinase (MLCK) and MLCK can then phosphorylate the myosins and promote muscle contraction
What allows myosin to bind actin in smooth muscled?
A PHOSPHATE ON THE MYOSIN LIGHT CHAIN
It’s not the same phosphate that came out of ATP either
If there is no calcium to allow MLCK to be active, which enzyme is active instead/
MLCP (myosin light chain phosphatase)
What prevents the filaments from interacting in smooth muscle?
Remember, there is no “chaperone”
DEPHOSPHORYLATION
What are the two ways that smooth muscle can be stimulated via pharmaco-mechanical coupling?
Hormones/neurotransmitters can either:
Open ligand gated Ca+ channels that bring in calcium from outside and then acts as a second messenger to induce calcium release from the SR
Activate IP3 which causes calcium release from the SR (no outside calcium)
What does electromechanical coupling do to stimulate smooth muscle?
DEPOLARIZATION opens VOLTAGE-gated Calcium channels and outside calcium comes in and acts as a second messenger to induce calcium release from the SR
What is the only type of smooth muscle that does electromechanical coupling to elicit calcium release from SR?
Single-unit smooth muscle
It’s unique to the muscles that do their own pacemaker
True or false: Both types of pharmacomechanical coupling can be used to elicit Ca release from SR in both single-unit and multiunit smooth muscle?
True
A decrease in contractile force occurs when the concentration of intracellular calcium _______
Decreases
What are the three mechanisms for decreasing intracellular Calcium in smooth muscle?
- SERCA pumping it back into the SR
- Sarcolemmal Na+/Ca+ exchanger (secondary active transport)
- Sarcolemmal Ca+ ATPase (Primary active transport)
How does the sarcolemmal Na+/Ca+ pump calcium out of the smooth muscle cell?
It uses secondary active transport using the energy from the sodium gradient that was established by the Na+/K+ ATPase pump.
Exchanges calcium for Na
What is the primary active transporter that provides the energy for the sarcolemmal Na+/Ca+ exchanger?
Na+/K+ ATPase
What are the two primary active transporters that directly reduce intracellular calcium in the smooth muscle?
- SERCA (sarcoplasmic reticulum Ca+ ATPase)
2. Sarcolemmal Ca+ ATPase
How is smooth muscle tone regulated by drugs?
- Amount of intracellular Ca+
2. MLCK to MLCP ratio
When calcium increases, what is the ratio of MLCK to MLCP?
MLCK will be more active than MLCP= more muscle contraction
How do calcium antagonists lead to vasodilation?
They block the voltage gated calcium channels, so no calcium can get in and bind with calmodulin, so the whole muscle stays relaxed
How do Potassium channel openers lead to vasodilation?
If you allow K+ to flow out, you will hyperpolarize the cell membrane, (bringing closer to -90mV) so it will be harder for the voltage gated Ca+ channels to open and let calcium in. Muscle stays relaxed
How do B2 adrenergic receptor agonists work to make smooth muscle cells in the alveoli relax?
They stimulate adrenergic receptors that results in cAMP getting made. cAMP is a second messenger that blocks MLCK.
No MLCK= no phosphates on myosin=no contraction
How do nitrates (like nitroglycerin) promote smooth muscle relaxation?
They promote the formation of cGMP
cGMP stimulates MLCP
More MLCP=less phosphate on myosin=no contraction
How do phoshopdiesterase inhibitors (like viagra) promote smooth muslce relaxation?
They inhibit the enzyme that degrades cGMP.
cGMP stimulates MLCP.
More MLCP=no phosphates on myosin=no muscle contraction
