3.3 Micturition Reflex

• What initiates the micturition contractions in the bladder?

  Stretch reflex from sensory stretch receptors
• Where are the sensory stretch receptors located that trigger the micturition reflex?

  In the bladder wall and posterior urethra
• How do sensory signals from the bladder reach the spinal cord?

  Through the pelvic nerves to sacral segments
• What happens to micturition contractions when the bladder is only partially filled?

  They usually relax spontaneously after a while
• What occurs as the bladder continues to fill regarding micturition reflexes?

  They become more frequent and cause greater contractions
• What does it mean that the micturition reflex is “self-regenerative”?

  Initial contraction increases sensory impulses and contractions
• What are the three phases of a complete micturition reflex cycle?

  Increase of pressure, sustained pressure, return to baseline
• What happens to the nervous elements of the micturition reflex after it occurs?

  They remain inhibited for a few minutes to an hour
• How does the micturition reflex influence the external sphincter?

  It inhibits the external sphincter to allow urination
• What role do brain centers play in the micturition reflex?

  They can inhibit or facilitate the reflex
• Where are the strong facilitative and inhibitory centers for micturition located?

  Mainly in the pons of the brain stem
• How do higher brain centers control micturition?

  By keeping the reflex partially inhibited until needed
• What happens when it is time to urinate regarding brain centers?

  They facilitate the micturition reflex and inhibit the sphincter
• How does voluntary urination begin?

  By contracting abdominal muscles to increase bladder pressure
• What is the typical outcome of voluntary urination?

  All urine is emptied, leaving minimal residue
• What are the key components of the micturition reflex process?

  • Stretch receptors in the bladder wall
  • Sensory signals to sacral spinal cord
  • Reflex contraction of detrusor muscle
  • Inhibition of external sphincter
  • Brain centers facilitating or inhibiting reflex
• What are the phases of the micturition reflex cycle?

  1. Progressive increase of pressure
  2. Sustained pressure period
  3. Return to basal tone of the bladder
• How does the brain influence the micturition reflex?

  • Keeps reflex partially inhibited
  • Can prevent micturition with sphincter contraction
  • Facilitates reflex when urination is desired