Ferguson reflex

The Ferguson reflex is the name given to the neuroendocrine reflex comprising the self-sustaining cycle of uterine contractions initiated by pressure at the cervix or vaginal walls. It is an example of positive feedback in biology. The Ferguson reflex occurs in mammals.

Mechanism

Upon application of pressure to the internal end of the cervix, oxytocin is released, which stimulates uterine contractions, which in turn increases pressure on the cervix (thereby increasing oxytocin release, etc.), until the baby is delivered.

Sensory information regarding mechanical stretch of the cervix is carried in a sensory neuron, which synapses in the dorsal horn before ascending to the brain in the anterolateral columns (ipsilateral and contralateral routes). Via the median forebrain bundle, the efferent reaches the PVN and SON of the hypothalamus. The posterior pituitary releases oxytocin due to increased firing in the hypothalamo-hypophyseal tract. Oxytocin acts on the myometrium, on receptors which have been upregulated by a functional increase of the estrogen-progesterone ratio. This functional ratio change is mediated by a decrease in myometrial sensitivity to progesterone, due to an increase in progesterone receptor A, and a concurrent increase in myometrial sensitivity to estrogen, due to an increase in estrogen receptor α. This causes myometrial contraction and further positive feedback on the reflex.^[1]

Research

It was originally studied among anesthetized rabbits.^[2] Studies among ewes demonstrated that it is blocked by epidural anesthesia.^[3] In their studies among mice, Niles Newton and colleagues demonstrated the importance of cortical influences.^[4] They enlarged to topic by introducing the term fetus ejection reflex.

The concept of cortical influences provided reasons to raise questions about the process of parturition among humans, characterized by a high encephalization quotient. Odent had observed that, in situations that are exceptionally rare, women can occasionally experience such a reflex, characterized by a birth after a short series of irresistible and powerful contractions without any room for voluntary movements. When a typical reflex occurs among humans there is an obvious elimination of neocortical control: women seem to be “on another planet”, talking nonsense, behaving in a way usually considered unacceptable regarding civilised women, finding themselves in the most unexpected, bizarre, often mammalian bending forward or quadrupedal postures

. It appears that among humans the primary and necessary phenomenon is a reduced neocortical activity.^[5]

References