3. THE STORAGE PHASE OF MICTURITION
OVERVIEW
‣ Micturition has two discrete phases
‣ the storage/continence phase
‣ urine is stored in the bladder
‣ the voiding phase
‣ urine is released through the urethra
‣ These phases require coordinated contraction/relaxation of the bladder and urethral
sphincters, which are all under control of the sympathetic, parasympathetic and somatic
nervous systems
‣ Learning Goal
‣ To look specifically at the storage phase of micturition, its regulation and consider
some clinical relevance
4. THE STORAGE PHASE OF MICTURITION
OVERVIEW
‣ The storage phase of micturition is controlled at the highest level
by continence centres of the brain
‣ These in turn control the continence centres of the spinal cord
‣ Storage of urine requires simultaneous
‣ relaxation of the detrusor muscle of the bladder
‣ contraction of both the internal (IUS) and external (EUS) urethral sphincters
‣ The bladder and IUS are primarily under the control of the
sympathetic nervous system
‣ The EUS is under the control of the somatic nervous system
6. THE STORAGE PHASE OF MICTURITION
SYMPATHETIC INNERVATION
‣ To stimulate storage, impulses from the cerebral cortex travel to
the pons
‣ The pons is responsible for coordinating the actions of the
urinary sphincters and the bladder
‣ the area involved in the storage phase is the pontine
continence centre
‣ From the pons, signals are sent to the sympathetic nuclei in the
spinal cord, and finally to the detrusor muscle and internal
urethral sphincter (IUS) of the bladder
7. THE STORAGE PHASE OF MICTURITION
SYMPATHETIC INNERVATION
‣ The impulses travel from the spinal cord to the bladder via the
sympathetic hypogastric nerve (nerve roots T10-L2)
‣ At the bladder, this stimulates:
‣ Relaxation of the detrusor muscle in the bladder wall
‣ via stimulation of β3-adrenoreceptors in the fundus and
the body of the bladder
‣ Contraction of the IUS
‣ via stimulation of α1-adrenoreceptors at the bladder neck
8. THE STORAGE PHASE OF MICTURITION
SOMATIC INNERVATION
‣ As described previously, the EUS is under voluntary somatic
control
‣ In the storage phase, impulses travel to the EUS via
the pudendal nerve (nerve roots S2-S4) to nicotinic
(cholinergic) receptors on the striated muscle, resulting in
contraction of the sphincter
‣ This coordinated relaxation of the detrusor muscle and
contraction of the urethral sphincters allows the bladder to
collect and store urine for many hours
9. THE STORAGE PHASE OF MICTURITION
SOMATIC INNERVATION
‣ As the bladder fills, the folds in the bladder walls (rugae)
flatten and the walls distend, increasing the capacity of the
bladder
‣ This means that as the bladder fills, it expands, allowing
the inner (intra-vesical) pressure to remain the constant
and lower than urethral pressure
‣ This process known as receptive relaxation is vital to the
storage of urine and prevents leakage during this phase
15. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ Which structure contracts during the storage phase of
micturition?
‣ Detrusor muscle
‣ Internal urethral sphincter
‣ Fundus of the bladder
‣ Body of the bladder
16. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ Which structure contracts during the storage phase of
micturition?
‣ Detrusor muscle
‣ Internal urethral sphincter
‣ Fundus of the bladder
‣ Body of the bladder
17. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ Which structure is under voluntary somatic control?
‣ Detrusor muscle
‣ Internal urethral sphincter
‣ External urethral sphincter
‣ Rugae of the bladder
18. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ Which structure is under voluntary somatic control?
‣ Detrusor muscle
‣ Internal urethral sphincter
‣ External urethral sphincter
‣ Rugae of the bladder
‣ The detrusor muscle (and hence rugae of the bladder) and
internal urethral sphincter are under control of the hypogastric
nerve.
19. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ Stimulation of which receptor would treat urinary
incontinence?
‣ Beta 1
‣ Beta 2
‣ Beta 3
‣ M3
20. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ Stimulation of which receptor would treat urinary incontinence?
‣ Beta 1
‣ Beta 2
‣ Beta 3
‣ M3
‣ Beta 3 agonists cause the detrusor muscle to relax and
therefore increase the bladder capacity.
21. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ What are the nerve roots of the pudendal nerve?
‣ S1-S3
‣ S2-S4
‣ L1-L2
‣ L5-S3
22. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ What are the nerve roots of the pudendal nerve?
‣ S1-S3
‣ S2-S4
‣ L1-L2
‣ L5-S3
23. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ The sympathetic nervous system acts on the internal
urethral sphincter via which receptor?
‣ Alpha 1
‣ Alpha 2
‣ Beta 2
‣ Beta 3
24. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ The sympathetic nervous system acts on the internal
urethral sphincter via which receptor?
‣ Alpha 1
‣ Alpha 2
‣ Beta 2
‣ Beta 3
25. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ Which nerve carries sympathetic innervation to the
bladder?
‣ Ilioinguinal nerve
‣ Hypogastric nerve
‣ Pudendal nerve
‣ Pelvic nerve
26. THE STORAGE PHASE OF MICTURITION
REVIEW QUESTIONS
‣ Which nerve carries sympathetic innervation to the
bladder?
‣ Ilioinguinal nerve
‣ Hypogastric nerve
‣ Pudendal nerve
‣ Pelvic nerve
28. THE VOIDING PHASE OF MICTURITION
OVERVIEW
‣ Micturition (urination) is the process of urine excretion from the
urinary bladder
‣ Most of the time, the bladder (detrusor muscle) is used to store urine
‣ As it fills, the rugae distend and a constant pressure in the bladder
(intra-vesicular pressure) is maintained
‣ This is known as the stress-relaxation phenomenon
‣ The ability to voluntarily control micturition develops from 2 years as
the CNS develops
29. THE VOIDING PHASE OF MICTURITION
MICTURITION
‣ Micturition is also known as the voiding phase of bladder
control and it is typically a short-lasting event
‣ Urinary flow rate in a full bladder is:
‣ 20-25ml/s in men
‣ 25-30ml/s in women
‣ The capacity of the bladder varies from roughly 300-550ml
‣ Afferent nerves in the bladder wall signal the need to void the
bladder at around 400ml of filling
30. THE VOIDING PHASE OF MICTURITION
REGULATION OF MICTURITION
‣ Passing of urine is under parasympathetic control
‣ Bladder afferents signals ascend through the spinal cord and then
project to the pontine micturition centre and cerebrum
‣ Upon the voluntary decision to urinate, neurones of the pontine
micturition centre fire to excite the sacral preganglionic neurones
‣ There is subsequent parasympathetic stimulation to the Pelvic
Nerve (S2-4) causing a release of ACh
‣ This works on M3 muscarinic ACh receptors on the detrusor muscle,
causing it to contract and increase intra-vesicular pressure
31. THE VOIDING PHASE OF MICTURITION
REGULATION OF MICTURITION
‣ The pontine micturition centre also inhibits Onuf’s nucleus, with
a resultant reduction in sympathetic stimulation to the internal
urethral sphincter causing relaxation
‣ Finally, a conscious reduction in voluntary contraction of the
external urethral sphincter from the cerebral cortex allows for
distention of the urethra and the passing of urine
‣ In the female, urination is assisted by gravity
‣ In the male, bulbospongiosus contractions and squeezing along
the length of the penis helps to expel all of the urine
35. THE VOIDING PHASE OF MICTURITION
REVIEW QUESTIONS
‣ Which nerve roots are mainly responsible for micturition?
‣ S3-5
‣ S2-4
‣ L1-3
‣ S1-5
36. THE VOIDING PHASE OF MICTURITION
REVIEW QUESTIONS
‣ Which nerve roots are mainly responsible for micturition?
‣ S3-5
‣ S2-4
‣ L1-3
‣ S1-5
37. References
These slide reflect a summary of the contents of
TeachMePhysiology.com and are to be used for
educational purposes only in compliance with the terms
of use policy.
Specific portions referenced in this summary are as
follows:
‣ https://teachmephysiology.com/urinary-system/micturition/storage-phase/
‣ https://teachmephysiology.com/urinary-system/micturition/voiding-phase-
micturition/
Additional sources are referenced on the slide
containing that specific content.
