Phys 5 Flashcards
What are the characteristics of multi-unit smooth muscle?
- the fibers operate individually (one nerve for multiple cells)
- examples: ciliary muscles of the eye, iris…
What are the characteristics of unitary smooth muscle?
- visceral smooth muscle or syncytial
- work together as a unit
- cell membranes there and contain gap junctions
- the type we mainly see in CP
- examples: GI tract, bile ducts, uterus…
Where does actin attach in smooth muscle?
dense bodies
What is unique about the myosin heads in smooth muscle?
they are bidirectional
Which has more actin: smooth or skeletal? myosin?
- smooth
2. skeletal
What is unique about the timing of smooth m. events?
- the myosin cross bridge cycling is slower
- the time myosin and actin are attached is longer (allows for greater contraction)
*this means that ATP demand is low (latch mechanism)
What replaces troponin in smooth m.?
calmodulin (CaM)
What can lead to increased Ca2+ in the cytosol?
- Nerves
- Hormones
- Environmental factors
- Stretch
How does calcium enter the cell?
Ca2+ L type channels
Calcium Entry Mxns
- Sarcolemmal
a. L type voltage gated Ca2+ channels
b. Receptor activated Ca2+ channels (ligand gated) - SR
a. InsP3 receptors
b. RYRs
Calcium Exit Mxns
- SERCA
- 3 Na/Ca antiporter
- Sarcolemmal Ca2+ ATPase
How does Calcium bind to CaM?
reversibly (it has 4 binding sites, and once Ca2+ binds it changes conformation and binds to actin/tropomysoin)
What does CaM activate?
-Myosin light chain kinase, which phosphorylates light chain of myosin, and this leads to the heavy chain being more active
What is contraction strength generally proportional to?
Ca2+ levels
What two mxns allow for smooth m. relaxation?
- Ca2+ pumps (remove the Ca2+)
2. Myosin light chain phosphatase (remove phosphate group from light chain)
What is the difference between depolarization and hormones/NTs in Ca2+ entry? Similarity?
- Depolarization uses voltage gated and H/NTs use ligand gated
- They both induce Ca2+ release from the SR
What two ways can hormones/NTs release Ca2+?
- Ligand gated channels
2. IP3
What are varicosities?
bulges on nerves that they serve as NT release sites (can release ACh and more)
Control of Smooth M:
- NE and Epi
- ACh
- Angiotensin II/vasopressin/endothelin I
- Adenosine
- NO
- CCK/Oxytocin/Serotonin/Histamine
- excitatory or inhibitory depending on receptors at target organ
- excitatory or inhibitory depending on organ (contraction is direct effect; relaxation can be indirect)
- contraction
- relaxation
- relaxation
- just listed
Environmental Controls of Smooth muscle
Hypoxia, excess CO2, increased H+, adenosine, LA, increased K+…—-> common vasodilators (common release is exercise)
What is the sequence of events on a G protein coupled pathway?
GPCR–>PLCy1–>PIP3–>IP3–>release of Ca2+ from SR
What is the RPM of smooth m?
-50 to -60 mV
What type of smooth m. can have APs?
unitary
What is a spiked potential?
- the spikes on top o the waves
- stimulated by hormones, NTs, stretch, spontaneous…
What are slow waves stimulated by? Plateaus?
- Oscillating Ca2+ influx (L type VGCCs) and K+ efflux (Ca2+ activated K+ channels)
- Stimulated by NTs and stretch
When do Ca2+ dependent K+ channels open?
with accumulation of Ca2+ (goal is to prepare for repolarization)
What ion is most important in smooth m. APs?
Ca2+ (way bigger of a player than Na+)
Latch mxn
- a way to increase tension while decreasing ATP usage
- dephosphorylation of the light chain
- attached cross bridges are still generating tension because they are still attached and have low affinity for ATP
What thin filaments are in skeletal m? smooth?
- Actin Tropomyosin, troponin
2. Actin, Tropomyosin
What’s the innervation of skeletal m? smooth?
- alpha motor neuron
2. Multiple (intrinsic, extrinsic (ANS))
What’s the difference between NMJ in skeletal vs. smooth?
skeletal has one, and smooth does not (varicosities)
NT receptors in skeletal? smooth?
- Nicotinic cholinergic
2. Muscarinic cholinergic, adrenergic…
Are APs required for both skeletal and smooth m?
nope, only for skeletal
*smooth can used pacemaker activity, IP3, hormonal
Why do we want smooth muscle?
- to maintain contraction
- contract periodically
- maintain organ shape
- continue to generate active tensility
- use relatively little ATP
Other forms of activation for skeletal? smooth?
- None
2. Paracrine, blood born, intrinsic
Steps of Smooth m. Contraction
- Ca2+ enters cytosol through PM Ca2+ channels (a little from SR)
- Ca2+ binds reversibly to CaM
- CaM-Ca2+ complex activates myosin light chain kinase (MLCK)
- Phosphorylated MLCK allows myosin and actin binding
- Relaxation
What is the key regulator for smooth m. relaxation?
myosin phosphatase because it removes phosphate from myosin (inactivates it)
What’s the difference between active and passive tension?
- what the cross bridges do
2. stretching of the muscle cell membrane
What is another name for Dense bodies?
adheren junctions
