Neuronal Control of Mictrution Flashcards
What are the functions of the nervous system to the lower urinary tract?
- provides sensations of the bladder filling and pain
- to allow bladder to relax and fill
- to initiate and maintain voiding so bladder can empty with minimal residual volume
- to allow regulation of smooth and skeletal muscle sphincters of the urethra
What is the PMC?
Pontine Mictruition Centre - a collection of neuronal cell bodies located in the pons in the brainstem involved in the supra spinal regulation of micturition
What are the 2 regions of the PMC?
L - sympathetic fibres associated with storage and relaxation of the bladder and contraction of the EUS - main role to facilitate the storage centre with function to keep EUS clamped down
M - parasympathetic NS involved in voiding
What happens to each centre when activated?
When the M centre is activated due to high levels of bladder stretch and conscious decision to void it inhibits the L centre causing inhibition of the sympathetics which relaxes the sphincters allowing you to void
What is the IUS?
Internal Urethral Sphincter - made of smooth muscle
What is the difference between the IUS in men and women?
More developed in men as it prevent retrograde ejaculation
Why would someone get retrograde ejactualtion?
One example is diabetes where the neurological control of the IUS is affected
What is the EUS?
External urethral sphincter - skeletal muscle
What does the EUS do?
It is under voluntary control - when decide to urinate you consciously contract this muscle to allow voiding
What happens to pressure and volume when urine enters bladder through ureters?
Bladder’s pressure doesn’t increase uniformly with volume until higher volumes (500ml) which is where pressure increases drastically
What happens in the voiding phase to pressure and volume?
Rhythmic contractions of the detrusor muscles gives a decrease in pressure and volume
What is a stretch receptor innervated by?
A sensory neurone
Where does the sensory neurone carrying information regarding stretch go to?
It enters spinal cord in sacral region at S2/3/4 and ascends up where it synapses on sympathetic neurone in region T10-L2 which projects on to post ganglionic which project to bladder in 2 places - detrusor and IUS
What is the role of the sympathetic?
They inhibit the detrusor and stimulate the IUS
What do the somatic motor neurones do?
They excite the skeletal muscle fibres in the EUS causing it to close
What nerve to the somatic motor fibres run along?
The pudendal nerve - important in continence and perineal sensation - can be anaesthetised in childbirth
What is a centre?
Area of grey matter that contain neurones that project down and synapse on pudendal neurones which switch on the excitatory function
Where does the afferent arm come from in the voiding phase?
The stretch receptors and enters the spinal cord at S2-S4 but it does synapse on the parasympathetic neurones which project up to the bladder
What is significant about the ganglion in parasympathetic neurones?
The ganglion in in the bladder wall - the parasympathetic pre ganglionic synapses on the short post-ganglionic
What is the effect of sensor neurone on the parasymapthetic?
Excitory
What is the effect of the sensory neurone on the detrusor?
Excitation
What is significant in babies about their control of micturition?
Babies don’t have myelinated pathways and only have simple reflex arc - when they reach a certain level of filling they have no control of their urination and just wee - have to wait til reflexes mature
What happens with high levels of bladder stretch?
Projects up to the brain stem activating the M centre which projects down onto parasympathetics creating a positive feedback loop allowing you to void ( as causes detrusor muscles to contract)
What receptors facilitate urination?
SYMPATHETIC - adrenergic on IUS are alpha 1 receptors
INHIBITORY receptors are B3 receptors
RECEPTORS ON VOIDING REFLEX is M3 receptors
SKELETAL MUSCLE IN TH EUS is nACh receptors
What drugs can act on Alpha 1 receptors and what is their role?
alpha 1 antagonists help to facilitate urination in lower urinary tract infection as cause IUS to relax allowing urination
What drugs can act on B3 receptors and what is their role?
overactive bladder is controlled by B3 agonists which relax the bladder
What drugs can act on M3 receptors and what is their role?
Anti-muscarinic drugs can cause urinary retention as they cause relaxation of bladder but not activate it enough using the parasympathetic voiding reflex
What happens to micturition is spinal lesion above S2?
transcended action of inhibitory neurones therefore PS neurone is not being inhibited so goes into overdrive causing micturition reflex to be overactive creating incontinence
What happens to micturition is spinal lesion between S2 and S4?
If lesion is between S2 and S3 you can’t feel how full bladder is or tell it to contradict - gives you overactive storage reflex as sympathetics still active causing your bladder to relax and get baggy and so full that urine trickles out - same is true for cauda equina syndrome as destroys motor outputs to bladder and sensory input to the bladder wall
