Micturition Reflex: Mechanism and Neural Control

Micturition Reflex: Mechanism and Neural Control

Question 1. What is micturition reflex? Describe the process of urine formation.
Answer:

Micturition:

• It is a process by which the urinary bladder empties itself when it becomes filled.

Micturation reflex:

• Micturition occurs by a reflex process called micturation reflex.
• It constitute of impulses initiated by the stretch receptors in the bladder wall, sensory signals, sacral segments of spinal cord, pelvic nerve then back urinary bladder and parasympathetic nerve fibers.

Mechanism:

Question 2. Describe the nerve supply of urinary bladder, and explain how contraction of detrusor muscle is stimulated. (or) Depict the innervation of urinary bladder with a neat labelled
Answer:

Nerve supply of urinary bladder:

• Urinary bladder is innervated by

1. Efferent nerve supply:

1. Sympathetic supply.

• Sympathetic fibers arises from the grey matter of L1 – L2 segments of spinal cord.
• These fibers descend down and form presacral nerve.
• Presacral nerve next divides into two hypogastric nerve which end in hypogastric ganglia.
• Post ganglionic fibers from here supply the bladder.
  Parts innervated and its action:

2. Parasympathetic supply.

• Preganglionic fibers lie in the gray matter of sacral segments of spinal cord.
• These fibers descend down and form pelvic nerve which end in hypogastric ganglia.
• Postganglionic fibers from the ganglia reach the bladder.
• Parts inverted and its action:

• The resultant effect is emptying of bladder.

3. Somatic nerve supply.

• Arises from the sacral segments of spinal cord.
• Passes through the pudendal nerve.
• Supplies posterior urethra and external sphincter.
• It helps the time of micturition reflex as it is voluntarily reflexed.

2. Affrent nerve supply:

Actions:

• Carry stretch sensation from the bladder along parasympathetic fibers.
• Carry pain sensation from bladder along sympathetic fibers.

Stimulation of contraction of detrusor muscle:

• Urinary bladder gets filled upto 450 ml.
• This increases pressure inside the bladder.
• Stretch receptors present on the wall of urinary bladder are stimulated.
• This generates sensory impulses which reach the sacral segments of spinal cord via fibers of pelvic nerve.
• Efferent impulses are produced in the spinal cord.
• These impulses travel to the bladder via efferent fibers of the pelvic nerve and causes contraction of detrusor muscle.