Cerebral blood flow (CBF) is autoregulated between mean arterial pressures of approximately 60–160 mmHg. The primary local vascular mechanism responsible for cerebral autoregulation is:
- A Myogenic response — cerebral arteriolar smooth muscle constricts when transmural pressure rises (Bayliss effect) and dilates when it falls ✓
- B Sympathetic vasoconstriction of cerebral arterioles via alpha-1 adrenoreceptors
- C Parasympathetic vasodilation via vagal fibres on cerebral vessels
- D Metabolic autoregulation via CO2-mediated changes in pH, which overrides all myogenic responses
Explanation
Cerebral autoregulation maintains constant CBF despite changes in perfusion pressure between 60 and 160 mmHg. The primary mechanism is the myogenic (Bayliss) response: cerebral arteriolar smooth muscle intrinsically constricts when perfusion pressure (and transmural pressure) rises, and dilates when it falls. Metabolic regulation (CO2/H+ changes modulating vascular tone) is also important and superimposed on myogenic tone. Sympathetic innervation plays a minor role in cerebral vessels. Below 60 or above 160 mmHg, autoregulation fails, and CBF becomes pressure-passive.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.