A special manifestation of the myogenic tone is the myogenic response (also called the Bayliss effect) in the vasculature. The Bayliss effect in vascular smooth muscle

Smooth muscle

Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...

s cells is a response to stretch. This is especially relevant in arterioles of the body. When blood pressure is increased in the blood vessels and the blood vessels distend, they react with a constriction; this is the Bayliss effect. Stretch of the muscle membrane opens a stretch-activated ion channel

Stretch-activated ion channel

Stretch-activated or stretch-gated ion channels are ion channels which open their pores in response to mechanical deformation of a neuron's plasma membrane. Stretch-activated channels were first observed in chick skeletal muscles by Falguni Guharay and Frederick Sachs in 1983 and the results were...

. The cells then become depolarized and this results in a Ca²⁺ signal and triggers muscle contraction

Muscle contraction

Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...

. It is important to understand that no action potential is necessary here; the level of entered calcium affects the level of contraction proportionally and causes tonic contraction. The contracted state of the smooth muscle depends on the grade of stretch and plays an important part in the regulation of blood flow.

Increased contraction increases the total peripheral resistanse (TPR) and this further increases the mean arterial pressure (MAP). This is explained by the following equation:


This effect is independent of nervous mechanisms and that is how we differentiate it from the myogenic tone, which is controlled by the sympathetic nervous system

Sympathetic nervous system

The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...

.

The overall effect of the myogenic response (Bayliss effect) is to decrease blood flow across a vessel after an increase in blood pressure.

History

The Bayliss effect (or Bayliss myogenic response) was discovered by physiologist Sir William Bayliss

William Bayliss

Sir William Maddock Bayliss was an English physiologist.He was born in Wolverhampton, Staffordshire and gained a B.Sc from London University. He graduated MA and DSc in physiology from Wadham College, Oxford....

 in 1902.

Proposed mechanism

When the endothelial cell in the tunica intima of an artery is stretched it is likely that the endothelial cell may signal constriction to the muscle cell layer in a paracrine fashion. Increase in blood pressure may cause depolarisation of the affected myocytes as well or endothelial cells alone. The mechanism is not yet completely understood, but studies have shown that volume regulated chloride channel

Chloride channel

Chloride channels are a superfamily of poorly understood ion channels consisting of approximately 13 members.Chloride channels display a variety of important physiological and cellular roles that include regulation of pH, volume homeostasis, organic solute transport, cell migration, cell...

s and stretch sensitive non-selective cation channels lead to an increased probability in opening of L-type (voltage-dependent) Ca²⁺ channels, thus raising the cytosolic concentration of Ca²⁺ leading to a contraction of the myocyte, and this may involve other channels in the endothelia.