Fill in the Blanks Alpha receptorsOnline version unit2 by Kirsten Storemski 1 Ca two hyperpolarization presynaptic opening block postsynaptic Ca K contract one depolarization Alpha receptors are located in the membrane of smooth muscles . It is the cause of of + channels . This causes + influx and therefore of smooth muscle in the PM . Therefore smooth muscle will . Alpha receptors are located on the membranes . It opens + channels . Therefore it causes of the presynaptic membrane . This will synaptic transmission .