1. Micturition
Domina Petric, MD

2. Neural control of micturition
Sensory afferents grow from dorsal root ganglion cells and innervate the walls of the urinary bladder.
These are MECHANO-SENSORY RECEPTORS that are sensitive to the stretch of urinary bladder walls.
There are also CHEMO-SENSORY elements associated with free nerve endings: chemical environment within the bladder lumen.

3. Neural control of micturition
Sensory informations travel via the anterolateral spinal cord pathway.
Sympathetic innervation is coming down from integrative centers in the brainstem and hypothalamus.
Intermediolateral cell column of the lower thoracal spinal cord and upper lumbar spinal cord is source of sympathetic innervation for urinary bladder.
Internal sphincter muscle is under the sympathetic control.

4. Neural control of micturition
Parasympathetic outflow comes from the sacral segments of the spinal cord.
It is recieving input from higher brain centers.
Detrusor muscle is under the parasympathetic control.

5. Neural control of micturition
Sympathetic innervation of the urinary bladder promotes bladder filling: relaxation of the bladder wall and contraction of the internal sphincter muscle.
Parasympathetic innervation of the urinary bladder promotes bladder emptying: contraction of detrusor muscle and relaxation of the internal sphincter muscle.

6. Neural control of micturition
There is somatic motor efferent that comes from the sacral segments of the spinal cord and innervates an external sphincter muscle in the floor of the pelvis.
Somatic control over the external sphincter muscle is important for appropriate and timely release of urine from the bladder.
Micturition is a result of coordinated parasympathetic and somatic motor control over urinary bladder.

7. Decrease of detrusor muscle tone: β3 adrenergic inhibition.
Bladder filling
Decrease of detrusor muscle tone: β3 adrenergic inhibition.
Increase of internal (urethral) sphincter muscle tone: 1 adrenergic excitation.

8. Decrease of the internal sphincter muscle tone: nitric oxide.
Bladder voiding
Increase of the detrusor muscle tone: M3 (muscarinic) cholinergic excitation.
Decrease of the internal sphincter muscle tone: nitric oxide.

9. Bladder voiding (micturition) Orbital medial prefrontal cortex
Amygdala
Hypothalamus
Bladder
voiding
(micturition)
MIDBRAIN PERIAQUEDUCTAL GRAY MATTER
Pontine micturition center
Parasympathetic preganglionic neurons
Inhibitory local circuit neurons
Parasympathetic postganglionic neurons
Somatic motor neurons
Bladder contraction and voiding

10. Literature
Leonard E White, PhD, Duke University