Micturition Flashcards
How does the micturition reflex change in children?
Initially is a spinal cord only reflex = no CNS control
As you toilet train: CNS control over the spinal reflex develops
What are the parasympathetic fibres called that control the motor component of the wall of the bladder and rectum? How may they be damaged?
Pelvic splanchnic nerves, S2-S4
Damage to sacral part of spinal cord can affect them
What’s the significance of the bladder being a pelvic organ? (in terms of where it sends its neurones to)
Upper part covered in peritoneum: visceral sensory neurones travel with sympathetic neurones to the spinal cord
Lower part not covered in peritoneum: visceral sensory neurones travel alongside parasympathetic nerves
Important for pain referral (T11-L2 or S2-S4)
Why and where will you feel stretching of the bladder as it fills?
Suprapubic area of the abdominal wall, anterior midline T12-L2 dermatome
Top of bladder sends visceral sensory neurones to T12/L1 spinal nerves
What are the 3 Ps that parasympathetic fibres are responsible for?
Pee, Poo, Point
Outline the process of micturition
Bladder fills, visceral sensory fibres activated by stretch receptors
Parasympathetic fibres: bladder contraction (detrusor smooth muscle) and internal urethral sphincter relaxation (different receptors to have different effects but to mediate bladder emptying)
Reduced APs in pudendal nerve S2-S4 relax the external urethral sphincter
= urine enters distal urethra
Which nervous systems are responsible for storage and emptying of urine?
Storage - sympathetic
Emptying - parasympathetic
Outline the storage of urine
Bladder wall/detrusor muscle relaxes and internal urethral sphincter contracts = sympathetic nerves
Increased APs in somatic pudendal nerve S2-S4 to increase tone in external urethral sphincter
How is continence maintained?
Contraction of external urethral sphincter by pudendal nerve
Why when you’re stressed/scared is it harder to pee?
Sympathetic NS activation = increased circulating NA causes increased tone in internal urethral sphincter so held tightly shut
Why are we able to void on demand?
Micturition control centres in pons and medulla can promote micturition reflex; relax external urethral sphincters and suppress storage pathways
What are the wall layers of the bladder?
Urothelium
Lamina propria
Detrusor smooth muscle
Adventitia connective tissue
What structures support the bladder?
Pelvic floor, perineal membrane
Levator ani ligament
Males: pubo-prostatic ligament
Females: pubo-vesical ligament
In which direction does the bladder expand?
Superiorly - superior to pubic bone
What are the 3 urinary sphincters in males and 4 in females?
Males: internal and external urethral sphincters + compressor urethrae
Females: interlay and external urethral sphincters + compressor urethrae + sphincter urethrovaginalis
