Control of micturition Flashcards
What stages does the bladder go through?
Storage phase
Micturition phase
What is the storage phase of the bladder?
Bladder fills with urine
How does the volume of urine in the bladder change during the storage phase?
Volume increases as it is filled with urine
How does the pressure in the bladder change during the storage phase?
Pressure increases slightly
Why does the pressure in the bladder increase only slightly during the storage phase?
Because the detrusor muscle relaxes
increasing the volume of space in the bladder
What causes the bladder detrusor muscle to relax?
Sympathetic post-ganglionic nerve fibres innervating it
What stimulates the sympathetic nerve fibres innervating the bladder detrusor muscle?
Sensory nerve fibres innervating bladder detrusor muscle
Where do sympathetic pre-ganglionic nerve fibres contributing to the innervation of the bladder detrusor muscle arise?
T10-L2
Where do sensory nerve fibres innervating the bladder detrusor muscle travel in the spinal cord?
Enter spinal cord at S2-S4
and then ascend up to T10-L2
Where do the sensory nerve fibres innervating the bladder detrusor muscle synapse with the sympathetic pre-ganglionic nerve fibres?
T10-L2
What stimulates sensory nerve fibres innervating the bladder detrusor muscle?
Stretch receptors in the bladder detrusor muscle
What happens to the internal urethral sphincter during the storage phase?
It is contracted
What stimulates the internal urethral sphincter to contract?
Sympathetic post-ganglionic nerve fibres
What happens to the external urethral sphincter during the storage phase?
It is contracted
What stimulates the external urethral sphincter to contract?
Somatic nerve fibres
What carries the somatic nerve fibres innervating the bladder from the spinal cord to the external urethral sphincter?
Pudendal nerve
What are the spinal nerve roots of the pudendal nerve?
S2-S4
What stimulates the somatic nerve fibres innervating the external urethral sphincter?
L centre
sends out excitatory nerve fibres that run down the spinal cord
Where is the L centre located?
Pons of brainstem
What do the sensory and sympathetic nerve fibres innervating the bladder detrusor muscle and internal urethral sphincter form?
Spinal reflex arc
What is the name of the spinal reflex arc responsible for the storage phase of the bladder?
Storage reflex
What is the micturition phase of the bladder?
Urine is released and expulsed from the bladder
What happens to the volume of urine in the bladder during the micturition phase?
Decreases
What happens to the pressure in the bladder during the micturition phase?
Increases and decreases
but overall it decreases
Why does the pressure in the bladder increase and decrease during the micturition phase?
Due to the bladder detrusor muscle undergoing contractions
Why does the the pressure in the bladder decrease overall during the micturition phase?
Due to expulsion of urine from bladder
What causes the bladder detrusor muscle to contract?
Parsympathetic post-ganglionic nerve fibres innervating it
Where do the parasympathetic pre-ganglionic nerve fibres contributing to innveration of the bladder detrusor muscle arise?
S2-S4
What stimulates the parasympathetic nerve fibres innervating the bladder detrusor muscle?
Sensory nerve fibres innervating the bladder detrusor muscle
Excitatory nerve fibres from M centre
Where is the M centre located?
Pons of brainstem
Where do the sensory nerve fibres innervating the bladder detrusor muscle synapse with the parasympathetic pre-ganglionic nerve fibres?
S2-S4
What stimulates the M centre?
Sensory nerve fibres innervating the bladder detrusor muscle generating high-frequency action potentials
Nerve fibres from cerebral cortex
How does the amount of stretch of the bladder detrusor muscle affect the stimulation of the sensory nerve fibres innervating the bladder detrusor muscle?
Small amount of stretch causes low frequency action potentials along sensory nerve fibres
Large amount of stretch causes high frequency action potentials along sensory nerve fibres
What does the M centre stimulate?
Stimulates parasympathetic nerve fibres innervating the bladder detrusor muscle even more
What does the M centre inhibit?
Inhibits the L centre
Inhibits the sympathetic nerve fibres innervating the bladder detrusor muscle and internal urethral sphincter
What inhibits the M centre?
Nerve fibres from cerebral cortex
What is the purpose of nerve fibres from the cerebral cortex stimulating or inhibiting the M centre?
Gives individual control over micturition as a whole
What do the sensory nerve fibres and parasympatheitc nerve fibres innervating the bladder detrusor muscle form?
Spinal reflex arc
What is the name of the spinal reflex arc responsible for the micturition phase of the bladder?
Micturition reflex
What type of receptor do sympathetic post-ganglionic nerve fibres innervating the bladder detrusor muscle act on?
B3 adrenoceptors
What type of receptor do sympathetic post-ganglionic nerve fibres innervating the internal urethral sphincter act on?
A1 adrenoceptors
What type of receptor do parasympathetic post-ganglionic nerve fibres innervating the bladder detrusor muscle act on?
M3 muscarinic receptors
