Uterus muscle Flashcards
Are Smooth muscle cells smaller or bigger than SKM cells?
Smaller
How many nuclei do smooth muscle cells have?
one
What are the myofilaments in smooth muscle cells?
- actin
- myosin
- no sarcomeres
How are myofilaments distributed in smooth muscle cells?
“random distribution”-> not striated (smooth)
What is the process of depolarization in smooth muscle cells?
LTCC –> Ca2+ influx (Ca2+ plateau lasts 10s-100s of msec)
Is the AP caused by Na+ influx for smooth muscle cells?
no
What is in charge of Repolarization in smooth muscle cells?
K+ channels(multiple types)
Is smooth muscle myogenic or neurogenic?
myogenic (muscle) - can trigger its own APs/contractions
What causes the “Slow Wave Depolarization” at rest?
mostly from Ca2+ influx through T-type Ca2+ channels
- Vm drifts up towards threshold-> fires APs
- Acts as a pacemake-> smooth muscle is myogenic
How do APs spread in smooth muscle cells?
- No T-tubules (bc no sarcomeres)
- AP spreads from cell to cell through gap junctions (cell are electrically connected)
- Group of smooth muscle cells act as a “single unit”- wave depolarization starts at one location and then spreads through all the connected cells
What occurs during Contraction?
A. Prolonged Ca2+ entry/ Slow Ca2+ removal - >long duration contractions
B. Slow myosin-actin interaction-> slow increase in tension; low ATP use (doesn’t fatigue)
What are the two sources of Ca2+ in smooth muscle cells?
- Sarcoplasmic reticulum
2. LTCC
What is the main source of Ca2+?
extracellular Ca2+ from LTCC
What are the steps for Triggering of Contraction in smooth muscle cells?
Ca2+ enters cell by LTCC and SR releases Ca2+ as well -> 4 Ca2+ come together and form CAM (calmodulin) -> stimulates MLCK (myosin light chain kinase) -> phosphorylates inactive myosin -> contraction
What are the steps for Relaxation in smooth muscle cells?
Voltage-dependent K+ channels activate during depolarization-> K+ begins to leave the cell-> Ca2+ activate K+ channels that are Ca2+ dependent-> both inhibit LTCC–> Na+ Ca2+ exchanger pumping 3 Na+ into cell and 1 Ca2+ out –> SERCA pumping Ca2+ back into SR –> MLCP (myosin light chain phosphatase inactivating myosin -> relaxation
What NT is parasympathetic?
ACh
What is the receptor for ACh for smooth muscle cells?
Muscarinic cholinergic
Which muscarinic cholinergic receptor activates the Gq pathway?
m3AChR
What happens when the Gq pathway is activated?
Contraction
What NT is sympathetic?
Norepinephrine (NE)
Which hormone is sympathetic?
Epinephrine (E) - from adrenal medulla
What type of receptors does NE and E bind to on smooth muscle cells?
Adrenergic
What type of receptor can both NE and E bind to on smooth muscle cells?
alpha 1
Which pathway is activated by alpha 1? What does it trigger?
Gq pathway- contraction (blood vessels, uterus)
What type of receptor can only E bind to on smooth muscle cells?
Beta 2
Which pathway is activated by beta-2 receptors? What does it trigger?
Gs pathway- relaxation (blood vessels, uterus, bronchioles)
What are the steps for Gq pathway?
G alpha q subunit stimulates PLC -> PLC acts on PIP2 and breaks it down to two molecules -> IP3 and DAG-> IP3 binds to IP3-R on SR to release more Ca2+ into cytosol-> DAG activates PKC-> PKC inhibits K+ channels and stimulates LTCC-> contraction
What is the steps for Gs pathway?
G alpha s subunit activates and stimulates AC (adenylate cyclase) -> AC converts ATP to cAMP-> cAMP activates PKA -> stimulates K+ channels and MLCP and inhibits MLCK -> relaxation
