Micturition reflex

Question 1

Neural Control of Micturition (Micturition Reflex)

Answer 1

1. Stretch receptors detect the filling of bladder, transmit afferent signals to spinal cord
2. Signals return to bladder from spinal cord segments S2 and S3 via parasympathetic fibers in pelvic nerve
3. Efferent signals excite detrusor muscle
4. Efferent signals relax internal urethral sphincter. Urine is involuntarily voided if not inhibited by brain
5. For voluntary control, micturition center in pons receives signals from stretch receptors
6. If it is timely to urinate, pons returns signals to spinal interneurons that excite detrusor muscle and relax internal urethral sphincter muscle. Urine is voided
7. If it is not the time to urinate, signals from pons excite spinal interneurons that keep external urethral sphincter contracted so that urine is retained in the bladder
8. When it is time to urinate, signals from pons cease and external urethral sphincter relaxes. Urine is voided

Question 2

What is micturition?

Answer 2

A process by which the urinary bladder empties when it becomes stretched
Involves two steps;
a) bladder progressively fills until the tension in its wall rises above threshold level
b) micturition reflex occurs

Question 3

Physiological anatomy of urinary bladder

Answer 3

1. The body - major part of the bladder in which urine collects
2. The neck - funnel-shaped extension of the body, connecting into the urethra

Question 4

What type of muscle is present in the bladder?

Answer 4

Smooth muscle - detrusor muscle

Question 5

What is trigone?

Answer 5

A small triangular area in the posterior wall of the bladder

Question 6

Innervations of bladder

Answer 6

1. Parasympathetic nerves (Pelvic nerves)
   - sensory (stretch)
   - motor (detrusor, internal sphincter)
2. Skeletal Motor fiber (Pudendal nerves)
   - sensory (stretch)
   - motor (external sphincter)
3. Sympathetic nerves (Hypogastric nerves)
   - sensory (fullness, pain)
   - motor (stimulate blood vessels)