Figure 1.

The relationship between wall tension, arterial diameter, membrane potential or [Ca²⁺]_i, and intraluminal pressure in rat cerebral arteries. Three phases of the diameter response to increased intraluminal pressure have been identified. As pressure is increased toward the normal physiologic range, myogenic tone (MT) begins to develop. Myogenic reactivity (MR) is observed within the physiologic pressure range, beyond which forced dilatation (FD) occurs as myogenic vasoconstriction fails to counteract the high intraluminal pressure. The myogenic response within the physiologic pressure range is shown in gray shading and is the difference between the diameter versus pressure curves in the absence and presence of extracellular Ca²⁺. Circumferential wall tension or stress is thought to be the stimulus for the myogenic response. Importantly, membrane potential (Em) and [Ca²⁺]_i increase as pressure is increased to 40 to 60 mm Hg, but exhibit modest changes over the physiologic pressure range. Redrawn from Figure 8 of Osol et al (2002).¹¹