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The muscle cells act as a syncytium, in which spontaneous depolarising pacemaker potentials occur. If these are above a certain threshold (known as the action potential) then a wave of calcium is released and a contraction occurs.
The muscle cells act as a syncytium, in which spontaneous depolarising pacemaker potentials occur. If these are above a certain threshold (known as the action potential) then a wave of calcium is released and a contraction occurs.
During labour the uterus can be divided into two regions, the upper, muscular region and the lower region which generally acts to provide a passive fibromuscular birth canal.
==Cervical Softening==
==Cervical Softening==
==Contractions==
==Contractions==
Contractions are high amplitude shortening and relaxing of muscles which occur with increasing frequency throughout labour. These contractions are responsible first for dilating the cervix, moving the foetus through the pelvis and eventually expelling the baby. The primary hormone involved is oxytocin, a protein (9 amino acids long) which is released following a nervous response which results from the weight of the baby on the cervix, among other things.
Oxytocin stimulates the decidual layer to release prostaglandins (which in turn enhance the effect of oxytocins). These act on the myometrium to produce a contraction by initiating the release of contraction associated proteins (CAP's) which:
Oxytocin stimulates the decidual layer to release prostaglandins (which in turn enhance the effect of oxytocins). These act on the myometrium to produce a contraction by initiating the release of contraction associated proteins (CAP's) which:
A high estrogen:progesterone ratio is required for contractions, as this results in an increase in the release of prostaglandins (by stimulating the release of phosphorlipase from lysosomes) and increasing the number of oxytocin receptors.
A high estrogen:progesterone ratio is required for contractions, as this results in an increase in the release of prostaglandins (by stimulating the release of phosphorlipase from lysosomes) and increasing the number of oxytocin receptors.
==Labour==
Labour is the clinical process of parturition. A mother tends to become aware of labour with either 2-4 rapid contractions within a 10 minute period or the breaking of the amniotic membranes (the "water breaking").
===Regulation===
Although the process is not entirely understood, scientists believe the hormone CRH and CRH binding proteins are responsible for regulating labour, as they induce placental release of estrogen and localised release of prostaglandins. Levels increase exponentially throughout pregnancy, and tend to be higher in mothers who give birth preterm.