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Micturition

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What are the three layers of the detrusor muscle?
Longitudinal
Spiral
Circular
What sensory receptors are present in the detrusor muscle? What nerves does it relay to (and spinal routes) and what NT/NTR?
Stretch
Sympathetic - L1 to L3
Pelvic N, pudendal and hypogastric
ACh and nAChR
What are the spinal routes of the somatic motorneurones innervating the external urethral sphincter? What may it also be influenced by (and when?)
S2-S4
Higher centres - micturition/storage centre
Constricts internal urethral sphincter during ejaculation
What is the parasympathetic innervation of the detrusor muscle? What NT/NTR? What is the outcome of stimulation?
S2-S4
contract detrusor via mAChR (M3)
Inhibits internal sphincter
What is bladder filling stimulated by? ANd how is it aided? What can obstructions cause?
Stretch
Peristaltic waves - 1 to 5 per minute
Renal Colic (can cause abdominal pain)
What graph may be used to measure micturition? At what volume do you have a strong urge to go? At what volume is the micturition reflex (and why does this occur?)
Cystometogram (P/V)
200ml
400ml - bladder near elastic limit
Why is the cystometogram flat?
p=2t/r
radius increases due to the storage reflex, so pressure doesn't increase by much
Describe the storage reflex?
Stretch detectors stimulated
Relax to sympathetic
Relaxes detrusor
Constricts I.U.S
Somatic neurone also stimulated (constricts external s)
Describe the micturition reflex?
Stretch receptors fire rapidly as tension increases
Information spent to pons (spinal cord)
- bladder fullness
- desire to go
parasympathetic input to bladder wall - contracts detrusor and relaxes I.sphincter
Somatic motor neurone is inhibited
Not a passive process - peristaltic waves
What are the three levels of control which an adult demonstrates?
1. Inhibition of reflex pathway
2. Increase tone of E.S.
3. Contraction of levator Ani/levator ani - supports base of bladder and reduces stretch
How is micturition initiated?
Contraction of diaphragm and abdo muscles (increases P)
Relax pelvic floor muscles (pulls bladder downwards)
Activity in higher centres - Pons
How is micturition maintained?
Receptors continue to discharge even though detrusor contracts
Flow of urine through the urethra causes reflex detrusor contraction and sphincter relaxation
Contraction of muscles helps expulsion
What happens to micturition after spinal cord damage?
Stretch receptors abnormally sensitive after damage - stimulates detrusor contraction
Motor neurones supplying ES activated
- inefficient bladder emptying
- detrusor-sphincter dysnergia
What are the problems associated with IBE?
- Retention of UTI
- May go up kidney and cause renal failure
- High pressure in urinary system