Lipids would be the answer
A specific protein called a receptor
I think Autorhythmic fibers are fibers that are self excitable or on their own for example some cardiac muscle. They repeatedly generate action potentials that trigger heart contractions.They continue to stimulate a heart to beat even when it is removed from the body. In comparison to contractile fibers, autorhythmic fibers are self excitable and do not require nervous system stimulation to trigger contractions. Contractile fibers have stable resting membrane potentials of -90mV, when a contractile fibers reaches threshold by action potential, the voltage gated fast sodium ions channels will open.
B) the less porous, the less permeable
Porous means "full of holes."
Permeable means "stuff can go through it."
The more porous something is, the more permeable it is.
Curiosity after a step is completed, when your new hypothesis is more probable than your prior one
