FREEBIES

Question 1

when SA node fibers have depolarized to +20mV, which of the following would be happening?

Answer 1

-peak positive value
-L-type channels close
-voltage-gated potassium channels open + start repolarizing the cell

Question 2

when threshold is reached in contractile cardiac fibers, what opens first?

Answer 2

-threshold is at -75mV in contractile fibers
-voltage-gated sodium channels open first + continue to depolarize the cell

Question 3

what is the sequence of events that leads to a reduction in the # of APs per minute in SA node fibers when stimulated by the parasympathetic nervous system

Answer 3

parasympathetic system is activated by periods of relaxation ->

parasympathetic neuron releases ACh onto muscarinic cholinergic receptors on SA node fiber ->

alpha subunit swaps GDP for GTP + disassociates away from beta/gamma ->

beta/gamma crawl to GIRK channels + activate them ->

GIRK channels increase the cells permeability to potassium ->

potassium starts leaving cell at a faster rate ->

the increase in potassium permeability leads to hyperpolarization, decreasing the # of APs per minute