Lecture 13 - Neurological control of micturition

Question 1

What autonomic system controls the storage phase and what is it?

Answer 1

Sympathetic NS

When volume increases in the bladder but pressure does not

Question 2

What does the sympathetic NS do?

Answer 2

Inhibits contraction of detrusor muscle in the bladder - relaxation

Stimulates the contraction of the internal urinary sphincter (IUS)

Question 3

What type of muscle is the EUS?

Answer 3

Skeletal - therefore under voluntary control

Question 4

What stimulates the sympathetic NS?

Answer 4

Stretch receptors in the bladder send afferent signals down a sensory neurone which synapses onto the sympathetic preganglionic neurone in T10/L2

Question 5

What are the sympathetic receptors?

Answer 5

Beta 3 adrenergic receptors - detrusor wall relaxation

Alpha 1 adrenergic receptors - IUS contraction

Question 6

IUS

Answer 6

Thickening in bladder wall at most proximal end of the urethra
Prevent retrograde ejaculation of semen into the bladder in males.
IUS well developed in males and not females

Question 7

L pontine storage centre

Answer 7

Area of grey matter that contains neurones that synapse onto the pudendal nerve

Located in the Barrington’s nucleus

Question 8

Pudendal nerve

Answer 8

Somatic motor fibres

Cause EUS to contract

Question 9

What spinal levels does the sensory neurone enter at?

Answer 9

S2, S3, S4

Question 10

What receptor does the pudendal nerve have?

Answer 10

nAChR - nicotinic acetylcholine receptors

Question 11

Parasympathetic control of bladder

Answer 11

Voiding response

Stimulates the bladder to contract

Question 12

What happens when there is high bladder wall stretching i.e. high volume of fluid stored?

Answer 12

The stretch receptors send afferents to the M centre in the brainstem

Question 13

M centre

Answer 13

Area of grey matter that contains neurones that stimulate the parasympathetic preganglionic nerve.
Therefore positive feedback.

Also inhibits the L centre and sympathetics.

Controlled by higher-order neurological functions neurones in the cerebral cortex that can inhibit or stimulate the M centre.

Question 14

Where is the parasympathetic postganglionic neurone found?

Answer 14

In the wall of the detrusor muscle

Question 15

What receptor does the parasympathetic postganglionic neurone have?

Answer 15

M3 (muscanaric)

Question 16

Why can’t babies control the urge to void?

Answer 16

They only have a simple parasympathetic reflex arc. The Neurone pathways have not yet myelinated so cannot inhibit the EUS

Question 17

Alpha 1 antagonists

Answer 17

Treats urinary retention

IUS relaxes

Question 18

B3 agonists

Answer 18

Treats overactive bladder

Detrusor muscles relaxes

Question 19

M3 antimuscarinics

Answer 19

Can cause urinary retention
Inhibits the parasympathetic stimulation on the detrusor muscles that would otherwise cause the detrusor muscle to contract

Question 20

Inhibitory projections in the spinal cord

Answer 20

Inhibit the parasympathetic preganglionic nerve

Question 21

Spinal cord lesion affecting the inhibitory projections

Answer 21

Loss of parasympathetic inhibition therefore overactive voiding

Question 22

Spinal cord lesion in S2,3,4

Answer 22

Parasympathetic preganglionic neurone damaged therefore cannot void.
Urinary incontinence and dribbling
Also seen in cauda equina

Question 23

Why does pressure not increase appreciably when volume increases in the bladder?

Answer 23

Stretch receptors send afferents to the sympathetic neurone which causes the detrusor muscle to relax

Question 24

Volume that initiates voiding response

Answer 24

500ml as bladder expands

Question 25

Diabetes

Answer 25

Can cause retrograde ejaculation as neural control on the IUS is affected (neuropathy)

Question 26

EUS

Answer 26

An integral component of the pelvic floor
Slow twitch striated skeletal muscle
Controls urination

Question 27

Pressure when voiding

Answer 27

Rhythmic contractions cause pressure spikes which slowly decreases pressure.

Question 28

Where is urine made and stored?

Answer 28

Made - kidney

Stored - bladder

Question 29

What epithelium lines the bladder?

Answer 29

Uroepithelium - transitional epithelium

Question 30

Describe the path of sympathetic innervation

Answer 30

1. Arise from T10- L2 spinal level
2. Passes through lumbar splanchnic nerves
3. Via superior hypogastric plexus to the right and left hypogastric nerves.
4. To the inferior hypogastric/pelvic plexus where the preganglionic fibres synapse
5. The postganglionic sympathetic neurone travels to the bladder wall via the distal hypogastric nerve

Question 31

Which brain centres inhibit micturition (M centre)?

Answer 31

Cortical

Suprapontine