Control of micturition

Question 1

What is micturition?

Answer 1

the normal process of the passive storage and active voiding of urine

Question 2

How is retrograde flow of urine prevented?

Answer 2

oblique angle of entry of ureters through bladder wall

Question 3

What muscles control the release of urine

Answer 3

Detrusor muscle:
- around bladder
- smooth muscle
- parasympathetic and sympathetic
- sensitive to stretch
Internal urethral sphincter:
- thickening of bladder musculature
- smooth muscle
- sympathetic supply
External urethral sphincter:
- striated muscle
- voluntary control via somatic NS

Question 4

Label the muscles involved in micturition

Answer 4

Question 5

Describe the somatic motor supply involved in micturition

Answer 5

Innervates external urethral sphincter
Pudendal nerve from S1-2
Contracts to retain urine
Voluntary

Question 6

Describe the parasympathetic supply involved in micturition

Answer 6

Pelvic plexus innervates detrusor muscle (S1-3)
ACh = neurotransmitter
Contracts muscle => squeezes and empties bladder

Question 7

Describe the sympathetic supply involved in micturition

Answer 7

• L1-4 outflow
• Norepinephrine = neurotransmitter
  Detrusor muscle:
• relaxes muscle to allow bladder to fill
• beta receptor
  Internal urethral sphincter:
• contracts sphincter to retain urine
• alpha receptor

Question 8

Describe the detrusor reflex

Answer 8

Increased vesicular pressure from bladder filling achieves threshold => detrusor muscle contracts
Contraction against urethral sphincter tone
Positive feedback mechanism

Question 8

Which areas of the brain control micturition?

Answer 8

Pons and cerebral cortex

Question 9

Describe the micturition reflex

Answer 9

Combination of detrusor reflex with inhibition of sympathetic and voluntary motor supply to bladder and urethra

Question 10

Describe function of autonomic bladders

Answer 10

No voluntary control of urination
Reflex pathways intact so bladder empties spontaneously

Question 11

Describe voluntary control of the bladder

Answer 11

Suppression of autonomic reflexes
If bladder overfilled, intact bladder will empty automatically

Question 12

what drugs are used for animals with weak bladder that cannot hold urine?

Answer 12

Alpha-sympathomimetic drugs:
- Increases internal urethral sphincter tone

Question 13

What is the effect of skeletal muscle relaxant on micturition

Answer 13

Decreases external urethral sphincter tone

Question 14

Describe the effects of parasympathomimetic drugs on micturition

Answer 14

Increased detrusor tone

Question 15

what is the action of alpha adrenergic blockers on micturition reflex

Answer 15

Relaxes internal urethral sphincter => urination