Micturition

Question 1

Describe the sympathetic innervation of the bladder?

Answer 1

• sympathetic efferents travel via the hypogastric nerve
• active during filling + storage phase of micturition
• maintains a tonic contraction of the internal urethral sphincter
• tonically inhibit the contraction of the detrusor muscle

Question 2

What receptors mediate inhibitory and excitatory actions on the detrusor muscle?

Answer 2

Inhibitory = beta receptors 
Excitatory = alpha receptors

Question 3

Which receptors act to keep the urethral sphincters closed?

Answer 3

alpha receptors

Question 4

What changes occur when the bladder wall starts to fill?

Answer 4

• walls of the bladder become stretched

- receptors in the walls detect the stretch and activate afferents in the pelvic nerves

Question 5

What happens when the afferents in the pelvic nerves become activated?

Answer 5

• afferents synapse on cells of the spinothalamic tract
• relays signal to the genital area of the somatosensory cortex
• person has a sense of bladder fullness

Question 6

How can a person inhibit micturition if the conditions are not appropriate?

Answer 6

• tighten the external urethral sphincter (skeletal muscle - voluntary control)

Question 7

Which nerve do the LMNs controlling the muscles of the external urethral sphincter run in?

Answer 7

Pudendal (S2-S4)

Question 8

What nucleus is the micturition centre found? Where is this nucleus located?

Answer 8

Barrington’s nucleus

located in the pons

Question 9

Describe the micturition reflex.

Answer 9

1. micturition centre activates descending fibres in the reticulopsinal tract
2. this inhibits the sympathetic and somatic outputs controlling the internal and external urethral sphincters
3. this activates the parasympathetic efferents
4. detrusor muscle is stimulated, causing the bladder to contract and urine to flow out of the urethra
5. once contraction of the detrusor starts, afferents in the muscle increase its activity by positive feedback - contraction continues until the bladder is empty

Question 10

Which receptors mediate the micturition reflex? Are the sympathetic or parasympathetic?

Answer 10

Muscarinic M3 receptors

Parasympathetic

Question 11

What are pathological storage/irritative symptoms of the lower urinary tract?

Answer 11

1. frequency
2. nocturia
3. urgency
4. urge incontinence

Question 12

What are pathological voiding/obstructive symptoms of the lower urinary tract?

Answer 12

1. hesitancy
2. straining
3. poor flow
4. intermittent
5. incomplete emptying

Also: terminal dribbling, dysuria, haematuria

Question 13

What is overactive bladder syndrome (OAB)?

Answer 13

• Urgency
• with or without incontinence
• frequency
• nocturia

Question 14

What can be used to treat/manage OAB?

Answer 14

antimuscarinics

prevent parasympathetic actions on the bladder

Question 15

What can be used to treat/manage urge incontinence?

Answer 15

1. anticholinergics (oxybutynin, tolterodine)
   - blocks ACh in parasympathetic nerves
2. beta-3 adrenergic (mirabegron)
   - beta-3 adrenoreceptors unregulated in OAB
   - HTN may be an issue
3. Botulinum Toxin A (Botox)
   - fuses synaptic vesicles with the motor end plate
   - hyper continence