Smooth Muscles Flashcards
What are the cell characteristics of skeletal muscle?
Long & cylindrical, multinucleated, heavily striated
What are the cell characteristics of cardiac muscle?
Branching networks, intercalated disks, single nucleus, lightly striated
What are the cell characteristics of smooth muscle?
Tapered at each end, nonstriated
What is the control of:
- Skeletal
- Cardiac
- Smooth
- Voluntary
- Involuntary
- Involuntary
Of the muscles, which have T tubules?
Skeletal + Cardiac
Of the muscles, which have the most developed SR?
Skeletal
Of the muscles, which have the least developed SR?
Smooth
What are the sources of calcium in the skeletal muscle?
SR
What are the sources of calcium in the cardiac muscle?
Extracellular fluid + SR
What are the sources of calcium in the smooth muscle?
Extracellular fluid + SR
Of the muscles, which have troponin?
Skeletal + Cardiac
Of the muscles, which do not have troponin?
Smooth
Of the muscles, which have gap junctions?
Cardiac, some in smooth
What are the neurotransmitters that are emitted from the initiation of smooth muscles?
Norepinephrine + Acetylcholine
With regards to smooth muscle, what does norepinephrine do?
Activates a- or b-adrenergic receptors
With regards to smooth muscle, what does acetylcholine do?
Activates muscarinic receptors
Action potentials in smooth muscle open what channel?
Calcium
In terms of speed, what is the difference in calcium and sodium channels?
Calcium channels open / close slower
What causes a plateau in an action potential?
Delay opening of potassium channel
Can smooth muscle be initiated w/o action potential?
Yes
What are the steps of initiation of smooth muscle w/o action potential?
- Neurotransmitter (e.g., Acetylcholine) activates muscarinic receptor
- Leading to activation of G protein
- Leading to activation of phospholipase C (PLC)
- Increases production of inositol-tris-phosphate (IP3)
- Stimulates calcium release from ER, which leads to calcium influx from extracellular fluid
What is the relation between oxygen and smooth muscle contractibility?
Low oxygen = relaxed
What is the relation between CO2 and smooth muscle contractibility?
High CO2 = relaxed
What is the relation between pH and smooth muscle contractibility?
Low pH = relaxed
What are the steps of smooth muscle contraction?
- Calcium ions come from outside of the cell or the ER.
- Calcium ions bind to calmodulin, which activates myosin light chain kinase (MLCK).
- MLCK hydrolyses ATP and phosphorylates myosin light chain.
- Phosphorylation activates myosin.
- Myosin-actin crossbridge cycling occurs (as in skeletal muscle).
- When calcium is pumped out of the cell, myosin light chain is dephosphorylated by myosin light chain phosphatase.
- The myosin becomes inactive, and the muscle relaxes.
