Can anyone please help me complete the dichotomous key attached on pg #103 for figures 1-8 on pg #102 (it is in the pdf of the textbook)?

these muscles maintain the blood pressure in the vessels. the smooth muscles are innervated by nerves of the autonomic nervous system. when the muscles contract, they cause vasoconstriction of the vessels and increase blood pressure. when the muscles relax, they enable vasodilation of the   blood vessels hence reduce blood pressure.  

not sure what it is

answer; synapse;