What controls the bladder?

Muscles

• Detrusor muscle: Contracts to empty the bladder during urination.
• Internal urethral sphincter: Automatically closes to prevent urine leakage.
• External urethral sphincter: Voluntarily controls urine flow.
• Pelvic floor muscles: Support the bladder and maintain continence.

Nerves

The bladder receives autonomic innervation from a network of nerves that include parasympathetic, sympathetic, and somatic fibres:

• Parasympathetic nerves. These nerves originate in the sacral spinal nerves (S2-S4) and travel through the pelvic nerve. They cause the bladder to contract and the internal sphincter to relax, which is what makes you urinate.
• Sympathetic nerves. These nerves originate in the lower thoracic and upper lumbar spinal levels (T10-L2) and travel through the hypogastric nerve. They cause the bladder to relax and the internal sphincter to contract, which is what stops you from urinating.
• Somatic nerves. These nerves originate in the sacral spinal nerves (S2-S4) and travel through the pudendal nerve. They provide voluntary control to the external urethral sphincter.

These nerves and receptors are involved.

• Pudendal nerve: Regulates external urethral sphincter function.
• Pelvic nerves: Coordinate detrusor muscle contraction and relaxation.
• Hypogastric nerve: Inhibits bladder contraction.
• Bladder stretch receptors: Detect bladder fullness, sending signals to the brain.

Organs and Systems

• Brain: Processes signals from bladder stretch receptors, controlling urination.
• Spinal cord: Coordinates nerve signals between the brain and bladder.
• Autonomic nervous system: Regulates involuntary bladder functions.
• Urothelium: The bladder lining, which helps detect fullness.

• Oestrogen: Maintains bladder health and function.
• Progesterone: Relaxes the detrusor muscle.
• Testosterone: Supports bladder muscle strength.