Smooth and cardiac muscle Flashcards
exam 3
Smooth vs skeletal muscle: strength
smooth muscle is stronger per gram of muscle
Smooth vs skeletal muscle: efficiency
Smooth muscle is more efficient and has greater variability
Smooth vs skeletal muscle: speed
Smooth muscle is slower due to slower cross-bride cycling
Smooth vs skeletal muscle: % of body mass
Smooth muscle is 10% of body weight; skeletal muscle is 40% of body weight
Smooth vs skeletal muscle: actin-myosin ratio
- Actin-myosin arrangement is less orderly than skeletal muscle (2:1)
- Larger proportion of actin in smooth muscle (10-20:1)
Smooth vs skeletal muscle: anchor
smooth muscle - dense bodies
skeletal muscle - z discs
Smooth vs skeletal muscle: SR
SR in smooth muscle is less developed - more dependent on outside Ca++ coming into cell because less Ca++ in SR
______ allows smooth muscle to maintain force of contraction for a long time while using minimal energy
“Latch” mechanism
Smooth vs skeletal muscle: myosin anatomy
- smooth - gap between myosin - allows greater shortening/stretching; heads pointed in opposite directions
- skeletal muscle has minimum shortening - no gap between myosin
Smooth vs skeletal muscle: shortening
smooth - half the size
skeletal - ~2cm
Smooth vs skeletal muscle: NT response
smooth: relax or contract (depends on receptor)
skeletal: contraction
What are the ways that Ca++ enters the cells for smooth muscle
leak channels
voltage-gated (L-type)
ligand-dependent
If Ca++ is 0, there will be no ____
BP - heart won’t work and no contraction bc it’s dependent on outside Ca++
most smooth muscle is _____ smooth muscle
visceral or unitary
Compare unitary (visceral) to multi-unit smooth muscle
Visceral/unitary - most of smooth muscle; gap junctions - coordinated contraction (intestines)
Multi-unit smooth muscle - no pathway for ions to move between neighboring cells - more graded (delicate) control; entirely dependent on NTs being released in area - ciliary and iris muscles in eye
The ______ is the only hybrid smooth muscle in the body
esophagus - has both unitary and multi-unit smooth muscle
Describe the 3 layers of the blood vessels
- Tunica Intima - endothelial (one layer thick) - capillaries
- Tunica Media - smooth muscle, middle layer
- Tunica Adventitia/Externa - Adventitia/outside layer; structural support
NO is produced in the _____
endothelium
In skeletal muscle, the NT is always ___
ACh
In smooth muscle, ACh causes ______ in the vasculature
relaxation
In smooth muscle, ACh causes ______ in the small intestine
contraction
Pacemaker cells have higher resting membrane permeability to _____ or ______
Na+(#1) or Ca++(#2)
Differentiate between the role of tropomyosin in smooth vs skeletal muscle
In skeletal muscle, tropomyosin gets in the way of myosin head being able to bind to active sites
In smooth muscle, active sites are always exposed (tropomyosin still there, but doesn’t do anuything)
The regulation of smooth muscle is determined by ______
myosin filaments - regulatory light chain, requires phosphorylation
Ca++ can be removed from the smooth muscle cell via
- SERCA - back into SR
To ECF: - Plasma membrane Ca++ ATPase (PMCA)
- NCX - 3 Na+ in for 1 Ca+ out
What determines MLCK activity?
Amount of Ca++ in cell (calmodulin binding)
Ca++ binds to _____ to activate MLCK
calmodulin
Voltage gated Ca++ channels in smooth muscle are ___ type
L
Myosin ______ adds a phosphate to myosin, while myosin _____ removes phosphate from myosin
MLCK - activates
phosphatase - inactivates
What are the two things that PKG can phosphorylate? What is the result?
- MLCK - reduces activity
- Ca++ entry channels - closes channels
What are the effects of NO in the vascular smooth muscle cell?
Increases activity of guanylyl cyclase - more cGMP - more relaxation through increased phosphatase activity of MLC or increased activity of PKG
How is NO made?
Endothelial cells turn arginine into NO via eNOS (endothelial NO synthase)
How can the activity of MLKC be reduced?
- remove the Ca++
- NO
How is eNOS activity increased?
neurotransmitters - ACh and bradykinin release Ca++ from their ER, interacts with calmodulin → increases activity of ENOS
How is cGMP inactivated?
- eventually falls apart (unstable)
- phosphodiesterase
How can you prolong the life of cGMP?
Phosphodiesterase inhibitor - sildenafil
Sildenafil was originally made to treat _______
pulmonary HTN
_____ is the only NT that can constrict brain blood vessels. What is the mechanism?
5-HT - binds to alpha 1 receptor
Describe the effects of an agonist binding to an alpha 1 receptor on a vascular smooth muscle cell
Increased PLC (phospholipase C) → cleaves a PG into DAG and IP3
- IP3 releases Ca++ from the SR → contraction
- DAG activates PKC → contraction
How can SSRIs treat headaches?
Reduce swelling in head via vasoconstriction
How can contraction of smooth muscle occur without an AP?
- Ca++ leaking into cell
- manipulation of the pathway via signaling compound
Discuss the different smooth muscle AP possibilities
Normal AP
Slow, rhythmic waves - pacemaker
AP with plateau - L type Ca++ channels, uterus
In heart muscle, where does the Ca++ that triggers an AP come from? How does this happen?
the SR - well developed
Ca++ induced Ca++ released - comes from outside initially
In heart muscle how much of the Ca++ comes from the SR vs ECF for an AP?
80% from SR
20% from ECF
Differentiate between T-type and L-type Ca++ channels
T-type - fast
L-type - slow
What is the trigger for Ca++ channels to open in a heart cell?
AP - Na+ entry
Where does the Ca++ come from that enters heart cells to trigger contraction?
T-tubules
How is the Ca++ removed from the heart cell after contraction?
Ca++ removed by SERCA pump (80%), remainder is removed from cell via NCX (primary, 15%) or plasma membrane Ca++ ATPase (PMCA) pump (5%) - towards end of Ca++ removal (low levels of ICF Ca++)
_______ is the Ca++ sequestering protein
Calsequestrin - a sequestering protein - takes something out of circulation (Ca++) and allows concentrated storage of Ca++ in the SR
Calsequestrin is found in ____ muscle cell with a SR
any
_______ is the inhibitor of the SERCA pump in the heart
Phospholamban - allows Ca++ to stay in sarcoplasm longer → more contraction from muscle
Phospholamban is only found in the _______
heart cells
Inhibition of Phospholamban would do what?
shorter length of contraction and faster resetting; increased HR
Differentiate between cholinergic and adrenergic activity in the heart
adrenergic - stronger/faster contraction
cholinergic - slower/weaker contraction
Discuss the modulation of cholinergic and adrenergic activity in the heart
cAMP dependent
- Beta activity → adenylyl cyclase → ATP → cAMP → PKA → stronger strength of contraction and HR
- mACh receptor activity - reduced cAMP production→ reduces activity of PKA → slower HR and weaker contractions
