From the Guidelines
Yes, detrusor muscle contraction is primarily controlled by the parasympathetic nervous system. When urination needs to occur, parasympathetic nerves originating from the sacral spinal cord (S2-S4) release acetylcholine, which binds to muscarinic receptors (specifically M3) on the detrusor muscle, causing it to contract. This contraction increases pressure within the bladder and facilitates urine expulsion. Simultaneously, the parasympathetic stimulation relaxes the internal urethral sphincter. This parasympathetic control explains why anticholinergic medications like oxybutynin, solifenacin, and tolterodine are effective in treating overactive bladder by blocking these muscarinic receptors, thus reducing unwanted detrusor contractions, as seen in studies such as 1.
The use of anticholinergic medications, such as oxybutynin, is supported by evidence from studies like 1, which indicates its effectiveness in treating detrusor overactivity in patients with neurogenic bladder. Conversely, sympathetic stimulation promotes detrusor relaxation and internal sphincter contraction, which helps with urine storage. Understanding this autonomic control is crucial for comprehending both normal bladder function and the pharmacological management of bladder disorders, as discussed in 1.
Key points to consider include:
- The parasympathetic nervous system plays a primary role in detrusor muscle contraction.
- Anticholinergic medications are effective in treating overactive bladder by blocking muscarinic receptors on the detrusor muscle.
- Sympathetic stimulation helps with urine storage by promoting detrusor relaxation and internal sphincter contraction.
- Understanding autonomic control of the bladder is essential for managing bladder disorders, as highlighted in studies such as 1.
From the Research
Detrusor Contraction Mechanism
- The contraction of the detrusor muscle is primarily controlled by the parasympathetic nervous system, which releases acetylcholine to stimulate muscarinic receptors on the detrusor smooth muscle 2, 3.
- The parasympathetic nervous system plays a crucial role in maintaining normal bladder function, including contracting the bladder smooth muscle and relaxing the bladder outlet during micturition 4.
- Muscarinic receptors, particularly M2 and M3 subtypes, are involved in the contraction of the detrusor muscle, with M3 receptors mediating direct contraction and M2 receptors contributing to indirect contraction 5, 4.
Role of Parasympathetic System
- The parasympathetic system is responsible for stimulating the detrusor muscle to contract, allowing for voiding of the bladder 3, 4.
- The release of acetylcholine from parasympathetic nerves and non-neuronal cells within the urothelium contributes to the contraction of the detrusor muscle 3.
- The parasympathetic system also plays a role in maintaining continence and regulating the bladder micturition cycle, although the exact mechanisms are not fully understood 3.
Muscarinic Receptors and Detrusor Contraction
- Muscarinic receptors, specifically M2 and M3 subtypes, are located on the detrusor smooth muscle and play a crucial role in regulating detrusor contraction 5, 4.
- The activation of M3 receptors by acetylcholine leads to direct contraction of the detrusor muscle, while M2 receptors contribute to indirect contraction by inhibiting sympathetically-mediated relaxation 5, 4.
- The balance between M2 and M3 receptor activity helps regulate detrusor contraction and relaxation, and alterations in this balance may contribute to bladder dysfunction 5, 4.