The physiologic "fear" response is associated with the signaling activity of adrenergic receptors stimulated by epinephrine and norepinephrine. b9b G protein–coupled receptor (GPCR) G protein–coupled receptor (GPCR) Protein Kinase C AKA adrenaline Protein Kinase A inositol 4,5-biphosphate diacylglycerol inositol triphosphate "There are ten known isoforms of adenylyl cyclases in mammals" [https://en.wikipedia.org/wiki/Adenylyl_cyclase] Activation "List of the steps involved in PKA activation: 1. Cytosolic cAMP increases. 2. Two cAMP molecules bind to each PKA regulatory subunit. 3. The regulatory subunits move out of the active sites of the catalytic subunits and the R2C2 complex dissconnects. 4. The free catalytic subunits interact with proteins to phosphorylate Ser or Thr residues." [https://en.wikipedia.org/wiki/Protein_kinase_A#Activation] Activation "List of the steps involved in PKA activation: 1. Cytosolic cAMP increases. 2. Two cAMP molecules bind to each PKA regulatory subunit. 3. The regulatory subunits move out of the active sites of the catalytic subunits and the R2C2 complex dissconnects. 4. The free catalytic subunits interact with proteins to phosphorylate Ser or Thr residues." [https://en.wikipedia.org/wiki/Protein_kinase_A#Activation] Phospholipidase C; "class of membrane-associated enzymes that cleave phospholipids just before the phosphate group" [https://en.wikipedia.org/wiki/Phospholipase_C] G protein–coupled receptor (GPCR) G protein–coupled receptor (GPCR) epinephrine signaling pathway PW:0000790 Pathway Ontology 9780813546773 ISBN The Fats of Life: Essential Fatty Acids in Health and Disease Rutgers University Press; ISBN 978-0-8135-4677-3 2010 Glen D. Lawrence norepinephrine signaling pathway PW:0000791 Pathway Ontology cardiac muscle cell CL:0000746 Cell Type classic metabolic pathway PW:0000002 Pathway Ontology hepatocyte CL:0000182 Cell Type cell of skeletal muscle CL:0000188 Cell Type