Bladder Innovation & Micturition Cycle

Question 1

What are the types of nerves controlling the bladder?

Answer 1

AUTONOMIC (involuntary control)
Sympathetic
Parasympathetic

SOMATIC (voluntary control)
Pudendal

Question 2

Function and location of parasympathetic nerves

Answer 2

Sacral region of the spinal cord
Provide motor innervation of the detrusor muscle
Inhibit the internal urethral sphincter

Question 3

Function and location of the sympathetic nerves

Answer 3

From the thoracic and upper lumbar regions of spinal cord

Promote contraction of the internal urethral sphincter

Question 4

What is micturition?

Answer 4

Also known as voiding

Emptying of the bladder

Question 5

What is the average bladder capacity of an adult?

Answer 5

700-800ml

Question 6

What happens when the bladder fills up?

Answer 6

• stretch receptors detect rugae unfolding and bladder is expanding/stretching (once above 200ml)
• they send messages to spinal cord
• creates a conscious desire to void as well as subconscious micturition reflex

Question 7

What is the micturition reflex?

Answer 7

• impulse to the bladder to contract
• at the same time as a nervous signal to internal sphincter to relax
• also inhibition of somatic nerves which contract the external sphincter
• want these to happen in a co-ordinated way so pressure/stress does not increase too much

Question 8

How do we not void at such a low volume (200ml)?

Answer 8

• micturition reflex is suppressed by conscious area of the brain
• until have socially acceptable time and place
• babies have not yet learnt this so void all the time and small amounts
• also somatic nerves are contracting external sphincter

Question 9

What co-ordinates micturition reflexes?

Answer 9

Pontine micturition center in the brainstem

Question 10

Filling & Voiding Cycle Graphs

Answer 10

LOOK AT GRAPHS FROM LEC

• filling takes much longer than voiding
• flow rate 0 during filling then up and down in voiding
• healthy bladder pressure in filling with be 0 and steady, in voiding goes up

Question 11

How to calculate flow rate from bladder volume?

Answer 11

dV/dt = flow rate

V = volume
t = time

Question 12

What is the maximum flow rate?

Answer 12

50ml/s

Question 13

What is the maximum bladder pressure?

Answer 13

100cm H2O

Question 14

How to calculate pressure?

Answer 14

Pressure = density (p) x gravity (g) x height (h)

Question 15

What is bladder compliance?

Answer 15

• how much the bladder can expand without increase in pressure
• 1/modulus or stiffness of the bladder
• change in volume/change in pressure
• Stiffer bladder = increase in pressure
• Softer relaxed bladder = fills without as much increase pressure
• As stiffness goes down, compliance goes up
• You want to have a high compliance

Question 16

What makes a healthy bladder compliant?

Answer 16

Rugae folds in wall

Made of SM so can expand over large distances

Question 17

What happens to urethral pressure over time?

Answer 17

In filling slight gradual increase

Voiding = urethral pressure drops down as sphincter releases then goes up as flows through urethra then down again

Question 18

Sphincter EMG

Answer 18

Electromyogram
Measures activity of the sphincter muscle
Increased ossilation as the sphincter contracts more during filling then disappear once voding begins

Question 19

What happens to detrusor pressure overtime?

Answer 19

No pressure during filling
In voiding rises quickly then back down again
Part of activation of detrusor pressure comes from drop in urethral pressure (need to be co-ordinated by pontine micturition centre)

Question 20

What type of muscle is the detrusor?

Answer 20

Smooth!