Lecture 13 - Neurological control of micturition Flashcards
What autonomic system controls the storage phase and what is it?
Sympathetic NS
When volume increases in the bladder but pressure does not
What does the sympathetic NS do?
Inhibits contraction of detrusor muscle in the bladder - relaxation
Stimulates the contraction of the internal urinary sphincter (IUS)
What type of muscle is the EUS?
Skeletal - therefore under voluntary control
What stimulates the sympathetic NS?
Stretch receptors in the bladder send afferent signals down a sensory neurone which synapses onto the sympathetic preganglionic neurone in T10/L2
What are the sympathetic receptors?
Beta 3 adrenergic receptors - detrusor wall relaxation
Alpha 1 adrenergic receptors - IUS contraction
IUS
Thickening in bladder wall at most proximal end of the urethra
Prevent retrograde ejaculation of semen into the bladder in males.
IUS well developed in males and not females
L pontine storage centre
Area of grey matter that contains neurones that synapse onto the pudendal nerve
Located in the Barrington’s nucleus
Pudendal nerve
Somatic motor fibres
Cause EUS to contract
What spinal levels does the sensory neurone enter at?
S2, S3, S4
What receptor does the pudendal nerve have?
nAChR - nicotinic acetylcholine receptors
Parasympathetic control of bladder
Voiding response
Stimulates the bladder to contract
What happens when there is high bladder wall stretching i.e. high volume of fluid stored?
The stretch receptors send afferents to the M centre in the brainstem
M centre
Area of grey matter that contains neurones that stimulate the parasympathetic preganglionic nerve.
Therefore positive feedback.
Also inhibits the L centre and sympathetics.
Controlled by higher-order neurological functions neurones in the cerebral cortex that can inhibit or stimulate the M centre.
Where is the parasympathetic postganglionic neurone found?
In the wall of the detrusor muscle
What receptor does the parasympathetic postganglionic neurone have?
M3 (muscanaric)
Why can’t babies control the urge to void?
They only have a simple parasympathetic reflex arc. The Neurone pathways have not yet myelinated so cannot inhibit the EUS
Alpha 1 antagonists
Treats urinary retention
IUS relaxes
B3 agonists
Treats overactive bladder
Detrusor muscles relaxes
M3 antimuscarinics
Can cause urinary retention
Inhibits the parasympathetic stimulation on the detrusor muscles that would otherwise cause the detrusor muscle to contract
Inhibitory projections in the spinal cord
Inhibit the parasympathetic preganglionic nerve
Spinal cord lesion affecting the inhibitory projections
Loss of parasympathetic inhibition therefore overactive voiding
Spinal cord lesion in S2,3,4
Parasympathetic preganglionic neurone damaged therefore cannot void.
Urinary incontinence and dribbling
Also seen in cauda equina
Why does pressure not increase appreciably when volume increases in the bladder?
Stretch receptors send afferents to the sympathetic neurone which causes the detrusor muscle to relax
Volume that initiates voiding response
500ml as bladder expands
