Sympathetic post-ganglionic transmission

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BlackTom AI · Accepted Answer

Question restatement: The topic is sympathetic post-ganglionic transmission, and we must evaluate which description correctly characterizes the signalling pathways involved for adrenergic receptors.
Option a: 'Acts only through the PLC-beta signalling pathway' would imply that all sympathetic post-ganglionic transmission uses PLC-beta exclusively. This is misleading because beta adrenergic receptors typically couple to Gs proteins that stimulate adenylate cyclase and increase cAMP, not PLC-beta, so this option ignores the well-established cAMP pathway for beta receptors.
Option b: 'Acts only through the Adenylate cyclase / cAMP signalling pathway' would ignore the fact that alpha-adrenergic receptors commonly couple to Gq proteins that activate PLC-beta and generate inositol trisphosphate (IP3) and diacylglycerol (DAG). Since alpha receptors can signal through PLC-beta, a statement asserting exclusivity to cAMP would be incomplete.
Option c: 'Involves beta adrenergic receptors acting through the Adenylate cyclase / cAMP signalling pathway and alpha adrenergic receptors acting through or the PLC-beta pathway' presents a mixed model: beta receptors signaling via AC/cAMP and alpha receptors signaling via PLC-beta (the Gq pathway). This aligns with the canonical dichotomy where beta receptors predominantly use the cAMP route, while alpha-1 receptors often engage PLC-beta signaling. The wording also allows for the alpha pathway to be active via PLC-beta, which is consistent with known alpha-1 signaling.
Option d: 'Involves alpha adrenergic receptors acting through the Adenylate cyclase / cAMP signalling pathway and beta adrenergic receptors acting through or the PLC-beta pathway' flips the typical coupling: alpha receptors are not predominantly linked to AC/cAMP signaling; they are primarily associated with PLC-beta via Gq. Similarly, beta receptors are not primarily coupled to PLC-beta. Hence this option misattributes the main pathways to each receptor type.
Option e: 'Involves alpha or beta adrenergic receptors that act either through the Adenylate cyclase / cAMP signalling pathway or the PLC-beta pathway' suggests that either receptor type can independently choose between pathways in all cases. In physiology, while there is diversity, the typical associations are more specific (beta with cAMP, alpha with PLC-beta). This option is overly vague and does not reflect the common, receptor-specific coupling patterns, making it an inaccurate generalization.
Overall, option c accurately reflects the complementary signalling roles of beta receptors via adenylate cyclase / cAMP and alpha receptors via PLC-beta, while the other choices correspond to oversimplifications or misattributions of receptor–pathway couplings.

Sympathetic post-ganglionic transmission

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