Which system contracts the bladder muscle when it is stretched?

The correct answer is the parasympathetic system, which plays a crucial role in the regulation of bladder function. Specifically, when the bladder is stretched due to the accumulation of urine, the parasympathetic system activates the detrusor muscle, which is the smooth muscle of the bladder wall. This activation leads to the contraction of the bladder, facilitating the process of urination.

The parasympathetic system is part of the autonomic nervous system, which manages involuntary bodily functions. Its role in bladder control is primarily about promoting relaxation of the internal sphincter and contraction of the bladder wall, enabling the storage and expulsion of urine in a coordinated manner. As the bladder fills, sensory receptors in the bladder wall send signals that prompt this response, illustrating the intimate connection between bladder volume and the function of the parasympathetic system.

The sympathetic nervous system, in contrast, generally inhibits bladder contraction during the storage phase to ensure that urine remains in the bladder. The corticostatic system is not directly related to bladder control; it pertains more to the regulation of various body systems by corticosteroids. The somatic nervous system primarily controls voluntary muscle movements and is not involved in the unconscious regulation of bladder muscle contraction.