Control of bladder function
The bladder performs only two functions, storage and voiding of urine. Control of these two mutually exclusive activities requires intact central and peripheral neural pathways. Neural programmes for each exist in the dorsal tegmentum of the pons, and suprapontine influences act to switch from one state to the other. The decision as to when to initiate voiding is determined by the perceived state of bladder filling and an assessment of the social circumstances.
As an individual may micturate once every 4 or so hours, and take only one or two minutes to void, the bladder is in storage mode for most of the time. During the storage phase, contraction of the detrusor smooth muscle in the bladder is prevented by inhibiting parasympathetic outflow. Closure of the bladder outlet is maintained by sympathetic influences on the detrusor smooth muscle in the bladder neck region and by contraction of the striated muscle of the urethral sphincter and pelvic floor innervated by the pudendal nerve. Voiding is initiated by a complete relaxation of the urethral sphincter and the reciprocal action of a sustained detrusor contraction, so that urine is effectively expelled.
To effect both storage and voiding, connections between the pons and the sacral spinal cord must be intact as well as the peripheral innervation which arises from the most caudal segments of the sacral cord (reviewed in Chapter 53). From there the peripheral innervation passes through the cauda equina to the sacral plexus and via the pelvic and pudendal nerves to innervate the bladder and sphincter. Thus the innervation needed for control of the bladder is extensive, requiring suprapontine inputs, intact spinal connections between the pons and the sacral cord, as well as intact peripheral nerves. Urinary continence is thus a severe test of neurological integrity.
An excellent review on the control of bladder function is available (de Groat, 1999).
Bladder dysfunction in neurological disease
Anterior regions of the frontal cortex are crucial for bladder control. This was shown by a series of patients with disturbed bladder control who had had various frontal lobe disturbances, including intracranial tumours, intracranial aneurysm rupture, penetrating brain injuries or prefrontal lobotomy (Andrew & Nathan, 1964).