Smooth Muscle Physiology Flashcards
Multiunit smooth muscle
One nerve ending goes to a single smooth muscle fiber.
Ex: ciliary muscles, iris, piloerector muscles.
Unitary smooth muscle
One nerve to a population of cells, and electrical component is transmitted through gap junctions.
Works as a unit.
Vast majority of smooth muscle.
Ex: GI tract, bile ducts, uterus.
Dense bodies/adherens junctions
Where actin binds (actin is much more populous in smooth muscle). Equivalent to Z disks.
What is the general rate of cycling of myosin cross-bridges?
Slower than skeletal muscle.
What is the general timeline that myosin and actin are attached?
They are attached longer and have a grater force.
Latch mechanism
When excitation slows, but contraction remains.
ATP demand is less.
A way to increase tension while decreasing ATP usage.
Dephosphorylation of light chain.
Ca 2+ concentration in the muscle cell can be controlled by:
Nerves, hormones, stretch, environmental ques.
Calcium can enter the cell via which ways across a sarcolemma? (2)
L-type VG Ca 2+ channels
Receptor activated Ca 2+ channels (ligand gated)
Calcium can enter the cell via which ways across from the SR? (2)
InsP3 receptors
Ryanodine receptors
The diversity of Ca 2+ channels functions how?
To fine-tune the needs of the cell.
Mechanisms of Ca 2+ exiting (3)
SERCA
3Na/Ca antiporter
Sarcolemmal Ca ATPase
Once Ca is release, it binds to ______, which activates _______ and allows for _______.
Calmodulin (CaM)
Myosin light chain kinase
Myosin and actin to bind
Relaxation of smooth muscle
Ca pumps remove the Ca from cytosol.
Myosin light chain phosphatase removes phosphate group
Summary of contraction of smooth muscle (8)
Increased Ca Binds CaM Increased myosin light chain kinase Phosphorylation of myosin light chains Increased myosin ATPase Myosin-P and actin bind Cross bridging Tension
Varicosities
Serve as NT release sites.
Release ACh among others.
Distance between varicosities and targets can be variable.
NE/Epi cause:
Adrenergic
Excitatory or inhibitory depending on organ.
ACh causes:
Cholinergic
Excitatory or inhibitory depending on organ.
Angiotensin II, vasopressin, endothelin-1 causes:
Contraction
Adenosine causes:
Relaxation
NO causes:
Relaxation
Environmental ques that control smooth muscle (4)
Hypoxia
Excess CO2
Increased H+
Increased K+
How is IP3 generated?
GPCR activated –> activates PLC –> generates IP3 which activates Ca release.
VDCC is a:
Membrane channel allowing Ca to enter cytosol and cause contraction.
Spiked potentials
Eventually enough potential to cause a spike.
Similar the phase 4.
Spike potentials are stimulated by:
Hormones, NTs, stretch.
Slow waves of smooth muscle activity
Oscillating Ca influx and K efflux.
Has pacemaker capabilities.
Plateaus are stimulated by:
NTs, stretch.
Calcium’s role in APs in smooth muscle
Ca is responsible for generating the AP instead of Na.
Fewer VG Na channels and more VG Ca channels.
Overall histology of smooth muscle:
Small, single nucleus, no striations.
SR in the smooth muscle:
Poorly developed SR, t-tubules.
Thin filaments in smooth muscle:
Actin and tropomyosin.
Thick filament composition in smooth muscle:
Myosin and ATPase activity is slow.
