13. Physiology of Smooth Muscle Flashcards
What is the same among skeletal and smooth muscle regarding muscle contraction?
Elevation in intracellular [Ca2+] for excitation-contraction coupling
The first major type of smooth muscle is multi-unit smooth muscle. The fibers operate individually and muscles are innervated by a single nerve. What are some examples of muscles that are this type?
Fine tuning muscles: ciliary muscles of the eye, iris and piloerector muscles
90% of muscle falls under unitary smooth muscle which is visceral smooth muscle which works as a unit. Cell membranes adhere and contain ________. What are some examples?
Contain gap junctions!
GI tract, bile ducts, uterus
There are no true sarcomere structures in smooth muscle. Where does actin attach and what arrangement do myosin heads have?
Actin attaches to dense bodies via adheren junctions
Myosin head have bidirectional arrangement
What is more in smooth muscle… actin or myosin?
Actin filaments are much more prevelant in smooth muscle and myosin is much more in skeletal M
Although the cycling of myosin cross-bridges are slower during contraction in smooth muscle because the ATPase is slower (less ATP used), the force is?
greater; The time myosin and actin are attached is greater = greater force
This is known as the latch mechanism
Caveolae are underdeveloped T tubule-like system. Step one of contraction in smooth muscle is Ca enters through the plasma membrane calcium channels. What is a difference regarding the SR?
Ca from SR is minor in smooth muscle (in skeletal muscle this is the major source). Calcium that does come from the SR is by IP3 gated release channels and ryanodine receptors
Calcium mainly enters from the sarcolemma via L type voltage gated Ca2+ channels and ?
Receptor activated Ca2+ channels (ligand gated) via hormones or NTs
How does calcium exit the cell? 2
SERCA (ca/atpase exchanger)
3Na/2Ca antiporter
Step two of contraction- after calcium is transported inside the cell- calcium will REVERSIBLY bind?
Calmodulin (which takes 4 Ca+) and changes confirmation into active form
Step 3 of contraction: Calmodulin-clacium complex will activate myosin light chains via? What happens?
MLCK (kinase) phosphorylates myosin, which activates it, allowing binding to actin (step 4)
When there is a high concentration of Ca2+ in the cell, there has to be a high amount of phosphorylation, which means?
the strength of contraction is stronger due to more myosin binding to actin to contract
Step 5 of contraction is relaxation, how does this step occur?
- calcium pumps remove calcium
- MLCP (phosphatase) removes phosphate group on myosin light chain.
** even if Ca2+ is gone, it doesnt relax until MLCP removes phophates**
What are the four major ways smooth muscle can be stimulated to contract?
- Nerves
- hormones
- Stretch
- Environment
Varicosities serve as NT release sites also called diffused junctions which can release acetylcholine as well as?
Norepinephrine/Epinerphrine
B2 adrenergic receptors cause dialation while Alpha 1 adrenergic receptors cause?
constriction
Adenosine and nitric oxide (NO) are inhibitory effectors and result in?
relaxation
What are the four main environmental ques that control smooth muscle?
- Hypoxia/Decrease O2
- Excess CO2
- Increased H+
- Adenosine, Lactic Acid, Increased K+ (etc)
ALL VASODIALTORS
Angiontensin II, vaspressin, and endothelin 1 all do what to smooth muscle?
Contraction
What are the two main pathways that increase intracellular Ca2+?
Voltage gated calcium channels, and ligand gated channels which respond to hormones and NTs
GPCR activated via hormones and NTs, activates pathways that influence voltage gated Ca/Na+ as well as activates PLC, which activates PIP2 which generates IP3, which binds to IP3R on the Sarcoplasmic reticulum and releases Ca2+
What are the two forms that action potentials occur in unitary smooth muscle?
Action potentials with plateaus
Spike potentials
Spike potentials are stimulated by hormones, neurotransmitters, stretch receptors. What are plateuas stimulated by?
NTs and stretch.
The latch mechanism is a way to increase tension while decreasing ATP usage. How does this work?
In latch mechanism… there is sustained stimulation, which keeps some Ca increased, allowing 20-30% contraction because the cycle proceeds slowly
Smooth muscle is able to continuously rearrange itself to reduce passive tension so it is able to stretch more. What is the difference in active tension between skeletal and smooth muscle?
Skeletal muscle has one optimal area where tension and length are best.
Smooth muscle due to actin rearrangment and aligning allows more stretch while also keeping tension relatively higher, where as in skeletal muscle we would see a drop once we pass a certain stretch length.
