A stroke can cause a range of bladder problems. This occurs due to the disruption of the brain-bladder communication channels. This post explores how it happens.
1. The bladder control mechanism
Figure 1 depicts the inside of a bladder.
The tubes (ureters) transport urine from our kidneys to the bladder. The bladder can store about 450-500ml of urine.
Its wall consists of a strong muscle layer, called the “detrusor muscle”. This muscle contracts to squeeze out urine when the specialized brain areas send messages to do so.
However, the brain should receive information from the stretching bladder wall about the increase in urine volume. This happens through a web of nerve endings that populate the outer layer of the bladder wall.
The message goes up to a place at the lower part of the brain stem.
2. The role of the two gates in the incontinence
Go through Figure 2. Find out the two control gates; these are named “sphincters” because they act like valves.
- The inner gate (named inner urethral sphincter)
- The outer gate (named outer (external) urethral sphincter).
We can find these gates near the tapering lower end of the bladder. As soon as the transit centre at the spinal cord receives approval from the brain, it messages the gates open, and the bladder wall contract. As a result, urine will flow out.
3. Brain areas that prevent incontinence problems
When the bladder wall muscle – detrusor – stretches with urine, the nerve network that covers its wall messages the centre at the Pons via the spinal cord. This centre, named “Pontine micturition centre”, seeks permission from its higher centres to activate the peeing reflex which it normally does. Under normal situations, the higher centres veto the Pons’ centre’s request until a suitable time and place is found to pee. In this way, the higher centres suppress this urgent message to contract from the bladder wall and relax the internal gate.
In contrast, the other route transports messages to inhibit wall contraction and close valves.
Stroke can disrupt brain-bladder communication causing continence problems.
Stroke kills neurons in areas where the blood supply is stopped. It happens either due to a blockage to the supply or a rupture of a carrying vessel. The former is called “ischemic stroke” and the latter is called “hemorrhagic stroke”. These stroke types are discussed in this post. When the disruption to the blood supply occurs in the areas that are responsible for peeing, peeing problems result.