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Flashcards in Neuronal Control Of Micturition Deck (19)
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How is the internal urethral sphincter controlled?

Smooth muscle


What is the role of the internal urethral sphincter?

Prevent incontinence
Prevent retrograde ejaculation in men


Which gender does not posses an internal urethral sphincter?



How is the external urethral sphincter controlled?

Skeletal muscle
Voluntary control


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

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


At what volume does the pressure in the bladder peak?

500 ml


How does the pressure change in voiding?

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


What are the nerve roots working on the bladder?

S2, S3, S4


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

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


Describe the sympathetic effects on the bladder

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


How do somatic nerves affect the bladder?

Closes external sphincter through storage phase
L centre stimulates somatic nerve to cause contraction of the sphincter


What is the role of the L centre?

Maintaining the storage phase


What is the action of PNS on the bladder?

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


Describe the reflex arc of the bladder

Stretch stimulates PNS, which in turn stimulates detrusor contraction


Micturition is what type of movement?

Simple spinal reflex


Describe micturition in babies

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


Describe how the M centre affects the bladder

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


How does the M centre inactivate the storage phase?

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


Describe the blanket term for the neuronal control of micturition

Descending modulation