Micturition Reflex

• The Micturition Reflex controls the act of urination through a combination of voluntary and involuntary mechanisms.
• It involves interaction between the central nervous system and the urinary tract.

Components of the Micturition Reflex:

1. Bladder

   • Function: The detrusor muscle in the bladder walls stores urine by relaxing and expels urine by contracting during urination.

2. Internal Urethral Sphincter

   • Function: Involuntarily controls urine flow from the bladder into the urethra. It relaxes during urination.

3. External Urethral Sphincter

   • Function: Under voluntary control, it allows individuals to start or delay urination.

Phases of the Micturition Reflex:

1. Filling Phase

   • Process: As the bladder fills, the detrusor muscle remains relaxed due to sympathetic nervous system activity, which also keeps the internal urethral sphincter contracted to store urine.

2. Storage Phase

   • Process: Afferent nerves send signals to the brain indicating bladder fullness, but the central nervous system inhibits the reflex, allowing voluntary control.

3. Voiding Phase

   • Process:
     1. Afferent signals indicate bladder fullness to the brain.
     2. The brain sends efferent signals via the parasympathetic nervous system.
     3. The detrusor muscle contracts, and the internal sphincter relaxes.
     4. Voluntary relaxation of the external urethral sphincter allows urination.

Control of Micturition:

1. Voluntary Control

   • Brain centers like the pontine micturition center (PMC) and the cerebral cortex control urination based on social and situational factors.

2. Involuntary Control

   • In infants and certain neurological conditions, involuntary urination occurs when the bladder reaches a specific volume due to undeveloped or damaged neural pathways.

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