WEEK 9. 9.6 Micturition; Autonomic Bladder Innervation Flashcards
(44 cards)
What is micturition
urination
How does urine reach the bladder?
Via peristaltic contractions of the ureters
What reflex is triggered when the bladder is full?
Stretch receptors in the bladder wall trigger the micturition reflex
When does the urge to urinate generally appear?
When the bladder contains 200 mL
What happens when the bladder contains around 500 mL ?
detrusor muscle contractions force the internal urethral sphincter open
In what instance can urination occur involuntary in individuals?
In infants, as their neurological pathway for control of external urethral sphincter has not yet been established
In the elderly, if their external urethral sphincter is not powerful enough to prevent urination
What role do stretch receptors play?
As the bladder fills with urine, stretch receptors detect this stretch and send signals to the spinal cord/brain to indicate the bladder is full
Explain the process of the spinal cord reflex in urination
- the spinal cord processes the signal from stretch receptors, and initiates an immediate involuntary reflex (micturition reflex)
- the reflex contracts the detrusor muscle of the bladder wall, increasing pressure in the bladder
- reflex relaxes the internal urethral sphincter
When are signals sent to the brain?
While the relaxation of the internal urethral sphincter is involuntary, signals are simultaneously sent to the brain for conscious awareness of the need to urinate.
How does voluntary control of urination then occur?
the brain then sends a signal back to the external urethral sphincter to relax/contract it, and urine flows through the urethra and out of the body
Describe the micturition reflex in 5 steps
- stretch receptors detect bladder filling, send a signal to spinal cord
- detrusor muscles surrounding bladder contract, causing urine to be squeezed out
- internal sphincter relaxes, enabling urine to exit bladder and enter urethra
- afferent neural signal is sent to brain, processes response and sends an efferent signal to urethra
- external sphincter relaxes/contracts, leading to urination or urine withholding
The urinary bladder receives input from what divisions of the PNS
the sympathetic and parasympathetic NS
What is the function of detrusor muscle?
muscles in the bladder wall that enable to bladder to contain more urine by relaxing
Sympathetic innervation affects what receptors in the bladder? and has what effect?
B3 receptors, relaxation of the bladder
parasympathetic innervation affects what receptors in the bladder? and has what effect?
M3 receptors, contraction of the bladder
The internal urethral sphincter is contracted via what?
sympathetic action, (a1 receptors)
What kind of innervation does the external sphincter receive
somatic
During urination, are the internal sphincter and external sphincter relaxed or contracted?
relaxed
During urination is the detrusor muscle contracted or relaxed?
contracted
What 3 systems is micturition under the control of?
the cortical centre, brainstem centre and spinal cord
What can damage to the 3 systems cause?
the inability of the body to voluntarily control urination, which can lead to involuntary urination (bladder dysfunction)
Describe the cortical system
Located in the cerebral cortex, the cortical centre provides voluntary control over initiation and inhibition of micturition through conscious decision-making and inhibition of the voiding reflex
Describe the brainstem
The brainstem centre consists of the pontine micturition centre (PMC) and periaqueductal grey (PAG), coordinating reflexive aspects of micturition, coordination between the bladder and external urethral sphincter
Describe the spinal cord
it serves as the final integration centre for micturition control, receives sensory info from the bladder and coordinating reflex arc that mediates coordinated contraction of detrusor muscle and relaxation of external urethral sphincter
