Neuronal Control of Mictrution

Question 1

What are the functions of the nervous system to the lower urinary tract?

Answer 1

1. provides sensations of the bladder filling and pain
2. to allow bladder to relax and fill
3. to initiate and maintain voiding so bladder can empty with minimal residual volume
4. to allow regulation of smooth and skeletal muscle sphincters of the urethra

Question 2

What is the PMC?

Answer 2

Pontine Mictruition Centre - a collection of neuronal cell bodies located in the pons in the brainstem involved in the supra spinal regulation of micturition

Question 3

What are the 2 regions of the PMC?

Answer 3

L - sympathetic fibres associated with storage and relaxation of the bladder and contraction of the EUS - main role to facilitate the storage centre with function to keep EUS clamped down
M - parasympathetic NS involved in voiding

Question 4

What happens to each centre when activated?

Answer 4

When the M centre is activated due to high levels of bladder stretch and conscious decision to void it inhibits the L centre causing inhibition of the sympathetics which relaxes the sphincters allowing you to void

Question 5

What is the IUS?

Answer 5

Internal Urethral Sphincter - made of smooth muscle

Question 6

What is the difference between the IUS in men and women?

Answer 6

More developed in men as it prevent retrograde ejaculation

Question 7

Why would someone get retrograde ejactualtion?

Answer 7

One example is diabetes where the neurological control of the IUS is affected

Question 8

What is the EUS?

Answer 8

External urethral sphincter - skeletal muscle

Question 9

What does the EUS do?

Answer 9

It is under voluntary control - when decide to urinate you consciously contract this muscle to allow voiding

Question 10

What happens to pressure and volume when urine enters bladder through ureters?

Answer 10

Bladder’s pressure doesn’t increase uniformly with volume until higher volumes (500ml) which is where pressure increases drastically

Question 11

What happens in the voiding phase to pressure and volume?

Answer 11

Rhythmic contractions of the detrusor muscles gives a decrease in pressure and volume

Question 12

What is a stretch receptor innervated by?

Answer 12

A sensory neurone

Question 13

Where does the sensory neurone carrying information regarding stretch go to?

Answer 13

It enters spinal cord in sacral region at S2/3/4 and ascends up where it synapses on sympathetic neurone in region T10-L2 which projects on to post ganglionic which project to bladder in 2 places - detrusor and IUS

Question 14

What is the role of the sympathetic?

Answer 14

They inhibit the detrusor and stimulate the IUS

Question 15

What do the somatic motor neurones do?

Answer 15

They excite the skeletal muscle fibres in the EUS causing it to close

Question 16

What nerve to the somatic motor fibres run along?

Answer 16

The pudendal nerve - important in continence and perineal sensation - can be anaesthetised in childbirth

Question 17

What is a centre?

Answer 17

Area of grey matter that contain neurones that project down and synapse on pudendal neurones which switch on the excitatory function

Question 18

Where does the afferent arm come from in the voiding phase?

Answer 18

The stretch receptors and enters the spinal cord at S2-S4 but it does synapse on the parasympathetic neurones which project up to the bladder

Question 19

What is significant about the ganglion in parasympathetic neurones?

Answer 19

The ganglion in in the bladder wall - the parasympathetic pre ganglionic synapses on the short post-ganglionic

Question 20

What is the effect of sensor neurone on the parasymapthetic?

Answer 20

Excitory

Question 21

What is the effect of the sensory neurone on the detrusor?

Answer 21

Excitation

Question 22

What is significant in babies about their control of micturition?

Answer 22

Babies don’t have myelinated pathways and only have simple reflex arc - when they reach a certain level of filling they have no control of their urination and just wee - have to wait til reflexes mature

Question 23

What happens with high levels of bladder stretch?

Answer 23

Projects up to the brain stem activating the M centre which projects down onto parasympathetics creating a positive feedback loop allowing you to void ( as causes detrusor muscles to contract)

Question 24

What receptors facilitate urination?

Answer 24

SYMPATHETIC - adrenergic on IUS are alpha 1 receptors
INHIBITORY receptors are B3 receptors
RECEPTORS ON VOIDING REFLEX is M3 receptors
SKELETAL MUSCLE IN TH EUS is nACh receptors

Question 25

What drugs can act on Alpha 1 receptors and what is their role?

Answer 25

alpha 1 antagonists help to facilitate urination in lower urinary tract infection as cause IUS to relax allowing urination

Question 26

What drugs can act on B3 receptors and what is their role?

Answer 26

overactive bladder is controlled by B3 agonists which relax the bladder

Question 27

What drugs can act on M3 receptors and what is their role?

Answer 27

Anti-muscarinic drugs can cause urinary retention as they cause relaxation of bladder but not activate it enough using the parasympathetic voiding reflex

Question 28

What happens to micturition is spinal lesion above S2?

Answer 28

transcended action of inhibitory neurones therefore PS neurone is not being inhibited so goes into overdrive causing micturition reflex to be overactive creating incontinence

Question 29

What happens to micturition is spinal lesion between S2 and S4?

Answer 29

If lesion is between S2 and S3 you can’t feel how full bladder is or tell it to contradict - gives you overactive storage reflex as sympathetics still active causing your bladder to relax and get baggy and so full that urine trickles out - same is true for cauda equina syndrome as destroys motor outputs to bladder and sensory input to the bladder wall