7.5. Renal Assessment and Micturition - Control of Micturition

Question 1

What gives parasympathetic nerve innervation to the bladder?

Answer 1

Pelvic nerves (S2-S4)

Question 2

What gives sympathetic nerve innervation to the bladder?

Answer 2

Hypogastric nerves (L1-L3)

Question 3

Is the parasympathetic motor innervation to the bladder rich or sparse?

Answer 3

Rich

Question 4

Is the sympathetic motor innervation to the bladder rich or sparse?

Answer 4

Sparse

Question 5

What does parasympathetic innervation to the bladder cause?

Answer 5

Increase in Detrusor muscle contraction

Question 6

What does an increase in Detrusor Muscle contraction result in?

Answer 6

This leads to an increase in pressure within the bladder

Question 7

What does sympathetic innervation to the bladder cause?

Answer 7

1. These prevent the reflux of semen into bladder during ejactulation
2. These inhibit bladder contraction
3. These close the internal urethral sphincter

Question 8

What innervates the skeletal muscle of the external urethral sphincter?

Answer 8

The somatic motorneurons formed from the Pudendal nerves (S2-S4)

Question 9

What provides sensory innervation from the bladder?

Answer 9

Stretch receptor afferents from the bladder wall

Question 10

How do the stretch receptor afferents work?

Answer 10

As the bladder fills, there is an increased discharge from the afferent nerves to the spinal cords, via interneurons

Question 11

What does the increase in discharge from the stretch receptor afferents result in?

Answer 11

1. Excitation of parasympathetic outflow
2. Inhibition of sympathetic outflow
3. Inhibition of somatic motorneurons to the external sphincter
4. Pathways to the sensory cortex causign the illusion of fullness

Question 12

What is micturition similar to?

Answer 12

A spinal reflex, that may be influenced by higher centres

Question 13

What is the process of micturition?

Answer 13

1. Stretch Receptors fire
2. Parasympathetic neurons fire / Motor neurons stop firing
3. Smooth muscle contracts and the internal sphincter is passively pulled open
4. The external sphincter relaxes

Question 14

What happens to the stretch receptors as the bladder becomes increasingly filled?

Answer 14

These are increasingly stimulated

Question 15

What is needed for micturition to occur?

Answer 15

1. Stimulation of the parasympathetic innervation to the Detrusor muscle
2. Relaxation of the External Sphincter by inhibition of the Somatic Motorneurons

Question 16

Who does the micturition reflex operate in, at the spinal cord level?

Answer 16

1. “Leaky” babies

2. Adults with spinal cord compression

Question 17

Why does the micturition reflex operate at the spinal cord level in babies?

Answer 17

Due to the higher brain connections are still needed to be establishe

Question 18

What is the volume of urine required to initiate the spinal reflex in adults?

Answer 18

300-350mls

Question 19

What does “potty training” involve?

Answer 19

The formation of the higher connections in the brain

Question 20

What are the two controlling pathways which are needed to be developed?

Answer 20

1. Delay

2. Voluntary initiation

Question 21

How is “Delay” accomplished?

Answer 21

It is accomplished by descending pathways from many brain centres, including the cortex and the brainstem

Question 22

What is involved in “Delay”?

Answer 22

1. Inhibition of the parasympathetic innervation
2. Stimulation of the somatic nerves to the external sphincter - thus overriding the inputs from the bladder stretch receptors

Question 23

What is involved in “Voluntary Initiation” of the descending pathways?

Answer 23

1. Stimulation of parasympathetic innervation

2. Inhibition of the somatic motorneurons, and thus summating with the stretch receptors

Question 24

What does Voluntary Urination involve?

Answer 24

1. Relaxation of the muscles of the pelvic floor

2. Perineal muscles and the external sphincter contraction

Question 25

How is relaxation of the muscles of the pelvic floor muscles involved in Voluntary Urination?

Answer 25

This can cause a downward tug on the detrusor muscle and initiate it

Question 26

How is contraction of the perineal / external sphincter muscles involved in Voluntary Urination?

Answer 26

1. These prevent urine flowing down the urethra

2. Interrupting flow once it starts

Question 27

What happens to the urine left in the urethra (after urination has stopped) in females?

Answer 27

The Urethra emptied via gravity

Question 28

What happens to the urine left in the urethra (after urination has stopped) in males?

Answer 28

This is expelled by contractions of the bulbocavernous muscle

Question 29

What are the 3 major types of abnormalities due to neural lesions?

Answer 29

1. Interruption of afferent nerves
2. Interruption of both afferent and efferent nerves
3. Interruption of facilitatory and inhibitory descending pathways from the brain

Question 30

What occurs in all of the neural cord lesions which effect the bladder?

Answer 30

Bladder contractions occur but are insufficient to completely empty the bladder

Question 31

How can patients train themselves to initiate voiding?

Answer 31

By pinching / stroking their thighs, leading to the mild mass reflex

Question 32

How does the mild mass reflex work?

Answer 32

1. After the spinal section, afferent stimuli irradiate from one reflex section.
2. When a relatively minor noxious stimulus is applied to the skin, it may radiate to autonomic nerve centres
3. This evokes bladder / rectal voiding

Question 33

What does the mild mass reflex allow for?

Answer 33

This returns some measure of voluntary control