Control of micturition

Question 1

What stages does the bladder go through?

Answer 1

Storage phase

Micturition phase

Question 2

What is the storage phase of the bladder?

Answer 2

Bladder fills with urine

Question 3

How does the volume of urine in the bladder change during the storage phase?

Answer 3

Volume increases as it is filled with urine

Question 4

How does the pressure in the bladder change during the storage phase?

Answer 4

Pressure increases slightly

Question 5

Why does the pressure in the bladder increase only slightly during the storage phase?

Answer 5

Because the detrusor muscle relaxes

increasing the volume of space in the bladder

Question 6

What causes the bladder detrusor muscle to relax?

Answer 6

Sympathetic post-ganglionic nerve fibres innervating it

Question 7

What stimulates the sympathetic nerve fibres innervating the bladder detrusor muscle?

Answer 7

Sensory nerve fibres innervating bladder detrusor muscle

Question 8

Where do sympathetic pre-ganglionic nerve fibres contributing to the innervation of the bladder detrusor muscle arise?

Answer 8

T10-L2

Question 9

Where do sensory nerve fibres innervating the bladder detrusor muscle travel in the spinal cord?

Answer 9

Enter spinal cord at S2-S4

and then ascend up to T10-L2

Question 10

Where do the sensory nerve fibres innervating the bladder detrusor muscle synapse with the sympathetic pre-ganglionic nerve fibres?

Answer 10

T10-L2

Question 11

What stimulates sensory nerve fibres innervating the bladder detrusor muscle?

Answer 11

Stretch receptors in the bladder detrusor muscle

Question 12

What happens to the internal urethral sphincter during the storage phase?

Answer 12

It is contracted

Question 13

What stimulates the internal urethral sphincter to contract?

Answer 13

Sympathetic post-ganglionic nerve fibres

Question 14

What happens to the external urethral sphincter during the storage phase?

Answer 14

It is contracted

Question 15

What stimulates the external urethral sphincter to contract?

Answer 15

Somatic nerve fibres

Question 16

What carries the somatic nerve fibres innervating the bladder from the spinal cord to the external urethral sphincter?

Answer 16

Pudendal nerve

Question 17

What are the spinal nerve roots of the pudendal nerve?

Answer 17

S2-S4

Question 18

What stimulates the somatic nerve fibres innervating the external urethral sphincter?

Answer 18

L centre

sends out excitatory nerve fibres that run down the spinal cord

Question 19

Where is the L centre located?

Answer 19

Pons of brainstem

Question 20

What do the sensory and sympathetic nerve fibres innervating the bladder detrusor muscle and internal urethral sphincter form?

Answer 20

Spinal reflex arc

Question 21

What is the name of the spinal reflex arc responsible for the storage phase of the bladder?

Answer 21

Storage reflex

Question 22

What is the micturition phase of the bladder?

Answer 22

Urine is released and expulsed from the bladder

Question 23

What happens to the volume of urine in the bladder during the micturition phase?

Answer 23

Decreases

Question 24

What happens to the pressure in the bladder during the micturition phase?

Answer 24

Increases and decreases

but overall it decreases

Question 25

Why does the pressure in the bladder increase and decrease during the micturition phase?

Answer 25

Due to the bladder detrusor muscle undergoing contractions

Question 26

Why does the the pressure in the bladder decrease overall during the micturition phase?

Answer 26

Due to expulsion of urine from bladder

Question 27

What causes the bladder detrusor muscle to contract?

Answer 27

Parsympathetic post-ganglionic nerve fibres innervating it

Question 28

Where do the parasympathetic pre-ganglionic nerve fibres contributing to innveration of the bladder detrusor muscle arise?

Answer 28

S2-S4

Question 29

What stimulates the parasympathetic nerve fibres innervating the bladder detrusor muscle?

Answer 29

Sensory nerve fibres innervating the bladder detrusor muscle Excitatory nerve fibres from M centre

Question 30

Where is the M centre located?

Answer 30

Pons of brainstem

Question 31

Where do the sensory nerve fibres innervating the bladder detrusor muscle synapse with the parasympathetic pre-ganglionic nerve fibres?

Answer 31

S2-S4

Question 32

What stimulates the M centre?

Answer 32

Sensory nerve fibres innervating the bladder detrusor muscle generating high-frequency action potentials Nerve fibres from cerebral cortex

Question 33

How does the amount of stretch of the bladder detrusor muscle affect the stimulation of the sensory nerve fibres innervating the bladder detrusor muscle?

Answer 33

Small amount of stretch causes low frequency action potentials along sensory nerve fibres Large amount of stretch causes high frequency action potentials along sensory nerve fibres

Question 34

What does the M centre stimulate?

Answer 34

Stimulates parasympathetic nerve fibres innervating the bladder detrusor muscle even more

Question 35

What does the M centre inhibit?

Answer 35

Inhibits the L centre Inhibits the sympathetic nerve fibres innervating the bladder detrusor muscle and internal urethral sphincter

Question 36

What inhibits the M centre?

Answer 36

Nerve fibres from cerebral cortex

Question 37

What is the purpose of nerve fibres from the cerebral cortex stimulating or inhibiting the M centre?

Answer 37

Gives individual control over micturition as a whole

Question 38

What do the sensory nerve fibres and parasympatheitc nerve fibres innervating the bladder detrusor muscle form?

Answer 38

Spinal reflex arc

Question 39

What is the name of the spinal reflex arc responsible for the micturition phase of the bladder?

Answer 39

Micturition reflex

Question 40

What type of receptor do sympathetic post-ganglionic nerve fibres innervating the bladder detrusor muscle act on?

Answer 40

B3 adrenoceptors

Question 41

What type of receptor do sympathetic post-ganglionic nerve fibres innervating the internal urethral sphincter act on?

Answer 41

A1 adrenoceptors

Question 42

What type of receptor do parasympathetic post-ganglionic nerve fibres innervating the bladder detrusor muscle act on?

Answer 42

M3 muscarinic receptors