MAC is defined as the minimum alveolar concentration of an agent that prevents movement in 50% of subjects in response to a standard surgical stimulus. The reflex arc mediating this endpoint is located primarily in which structure?

• A Spinal cord ✓
• B Cerebral cortex
• C Reticular activating system of the midbrain
• D Medullary vasomotor centre

Explanation

Immobility in response to noxious stimulus, the endpoint of MAC, is mediated at the level of the spinal cord, as shown by decerebrate and spinal cord transection studies where volatile agents still suppress movement. This distinguishes MAC from MAC-awake, the concentration permitting response to command, which is a cortical endpoint and roughly one third of MAC. The reticular activating system and medulla relate to consciousness and autonomic function, not immobility.

Reference: Miller's Anesthesia, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.