Neuronal Control Of Micturition

Question 1

How is the internal urethral sphincter controlled?

Answer 1

Smooth muscle

Involuntary

Question 2

What is the role of the internal urethral sphincter?

Answer 2

Prevent incontinence

Prevent retrograde ejaculation in men

Question 3

Which gender does not posses an internal urethral sphincter?

Answer 3

Females

Question 4

How is the external urethral sphincter controlled?

Answer 4

Skeletal muscle

Voluntary control

Question 5

What would we discover if we insert a catheter into the bladder and fill it with water?

Answer 5

Measuring the pressure
Find that the pressure remains remarkably constant to a point
(Storage phase)

Question 6

At what volume does the pressure in the bladder peak?

Answer 6

500 ml

Question 7

How does the pressure change in voiding?

Answer 7

Peaks and drops in pressure until back at the normal pressure of empty bladder

Question 8

What are the nerve roots working on the bladder?

Answer 8

S2, S3, S4

Question 9

Describe what happens to the stretch receptors when there are low volumes in the bladder

Answer 9

Under low frequency/firing
Signals along afferent sensory fibres to the spinal cord (between S2-4)
Theses fibres ascend and synapse with sympathetic fibres between T10-L2

Question 10

Describe the sympathetic effects on the bladder

Answer 10

Activated by low firing of stretch receptors
Causes relaxation of the detrusor muscle to prevent increased pressure as the bladder fills
Also causes contraction of internal sphincter

Question 11

How do somatic nerves affect the bladder?

Answer 11

Closes external sphincter through storage phase

L centre stimulates somatic nerve to cause contraction of the sphincter

Question 12

What is the role of the L centre?

Answer 12

Maintaining the storage phase

Question 13

What is the action of PNS on the bladder?

Answer 13

Sensory fibres from the stretch receptors activate PNS when signals are high
Increased volumes in the bladder
PNS acts to contract the detrusor muscle

Question 14

Describe the reflex arc of the bladder

Answer 14

Stretch stimulates PNS, which in turn stimulates detrusor contraction

Question 15

Micturition is what type of movement?

Answer 15

Simple spinal reflex

Question 16

Describe micturition in babies

Answer 16

Babies have no control over this reflex
(No modulation)
Emptying of bladder is automatic at a certain volume

Question 17

Describe how the M centre affects the bladder

Answer 17

Stimulates the PNS which stimulates micturition
Increased frequency in sensory neurones stimulate the M centre
Cortex sends inhibitory projections down onto M centre to prevents us urinating ourselves
When you get to a toilet, the cortex sends excitatory/stimulatory signals to the M centre to initiate urination

Question 18

How does the M centre inactivate the storage phase?

Answer 18

Switches off the L centre to cause relaxation of external sphincter
Switches off sympathetics to relax the internal sphincter

Question 19

Describe the blanket term for the neuronal control of micturition

Answer 19

Descending modulation