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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.
==Cervical Softening==
The [[cervix]] consists largely of fibrous collagen in a proteoglycan matrix. It is normally hard, and needs to be softened to allow passage of the baby. The presence of keratan sulfate decreases the amount of collagen, whereas dermatan sulfate increases the amount of collagen.
There are several chemicals which allow the softening of the cervix, including:
* Metalloproteinases
* Proinflammatories such as cytokines which induce an inflammatory response
* Nitrous oxide (although not directly responsible it is the product following the catabolism of inhibiting NOS)
* Prostaglandins
==Contractions==
The 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:
* increasing gap junctions between cells to increase the effectiveness of the synctium and increase the likelihood that an action potential will occur
* increasing ion channels for calcium to increase the effect of an action potential
* increasing oxytocin and prostaglandin receptors to enhance the above two effects
Calcium induces the production of myosin light chain kinase, which in turn induce contractions.