Micturition Reflex.

 

Introduction.

• Micturition is the process by which the urine stored in the urinary bladder is excreted out of the body.

• In simple terms “Micturition” is the scientific name of the process of urination.

• It is the result of involuntary and voluntary opening of internal and external urethral sphincters.

• When the bladder is filled with urine around 150ml there is an urge to urinate, while it can be easily ignored.

• When the bladder is filled by urine around 300-400 ml the urge to urinate becomes hard to ignore which results in opening of both the urethral sphincters causing excretion of the urine.

• The nerves which play an important role are;

• Pelvic nerve.

• Pudendal nerve

• Hypogastric nerve.

• The receptors from which actions are initiated are,

• B3 receptors (causes relaxation of detrusor muscles in bladder wall)

• M3 receptors (causes contraction of detrusor muscles in bladder wall)

• Nicotinic receptors (causes contraction of muscles of external urethral sphincter)

• The process of micturition involves following steps;

• On filling of the urinary bladder, the stretch receptors in the bladder get activated.

• Stretch receptors send faster impulses to the sacral micturition center located in the sacral region.

• The impulses are then relayed to “Pons' ' in the brain which activates parasympathetic nerves which cause contraction of detrusor muscles through M3 receptors.

• Internal urethral sphincter opens involuntarily following contraction of the bladder.

• External urethral sphincter is guarded by skeletal muscle which is relaxed by voluntary control causing voiding (urination).

• When we are controlling the urination we are actually firing the “Pudendal Nerve” which causes contraction of the external urethral sphincter.

Commonly Asked Question.

1. Write a short note on “Micturition Reflex”.