Micturition - Anatomy & Physiology

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Micturition is the normal process of the passive stoage and active voiding of urine.

Storage and Voiding

Under neurological control

• Bladder
  • Smooth muscle
• Urethra
  • Smooth muscle
  • Skeletal muscle

Innervation Involved in the Reflex

Sensory

The fullness of the bladder is detected by stretch sensitive nerve endings in the bladder wall

Motor

The motor components of the reflex are the Detrusor Muscle, Internal Urethral Sphincter and the External Urethral Sphincter. They former two are supplied by the autonomic nervous system with the latter being of somatic innvervation.

• The general aim for the sympathetic and somatic systems is to retain urine
• The general aim for the parasympathetic system is to void urine

Somatic Motor Supply

• S1-S2
• Pudendal Nerve
• No synapse
• Innervates the urethral skeletal muscle - external urethral sphincter
• Function is to retain urine

Parasympathetic Supply - Bladder

• S1-S3
• Synapse in pelvice plexus or bladder wall
• Innvervate the detrusor muscle
• Action - excitatory
• Function - empty bladder

Sympathetic Supply - Detrusor Muscle

• L1-L4
• Syanpse in caudal mesenteric ganglion - bladder wall
• Receptor - beta
• Inhibitory action
• Allows bladder filling

Sympathetic Supply - Internal Urethral Sphincter

• L1-L4
• Synapse in caudal mesenteric ganglion
• Receptor - alpha
• Excitatory action
• Function - retain urine through increased urethral tone

Central Connections

There is aspects of control by the Pons and the Cerebral Cortex with possible influences from the cerebellum.