Neurological Control of Micturition Flashcards
Describe the bladder
Smooth muscle bag – when contracts = empties
Control by the autonomic nervous system
Stores urine
Detrusor muscle = layer of the wall
Describe the internal urethra sphincter (IUS)
Smooth muscle
Well developed in men
Prevents retro-grade ejaculation = no semen enters the bladder
In DM the neural control of the sphincter is affected
Alpha 1 receptors
Describe the external urethral sphincter (EUS)
Skeletal muscle
Integral component of pelvic floor
Voluntary control
nAChR
What enables the bladder to increase in volume but pressure remains unchanged?
Expansion of smooth muscle
Storage phase until 500ml = pressure spike (max vol)
Outline the voiding phase of the bladder
Emptying
Contractions of the detrusor muscle = spikes as volume decreases
Relaxation of the IUS/EUS
Outline the neural control of the voiding phase (voiding reflex)
Parasympathetic
Stretch receptor bladder – sensory neurone to S2-S4 – synapse with parasympathetic neurones – parasympathetics project back to bladder = stim contraction of detrusor
M centre activated by HIGH bladder pressure (stretch receptors) = stimulate parasympathetics (+ve feedback)
Control of M centre = excitatory/inhibitory neurones
Outline the neural control of the storage phase (storage reflex)
Sympathetic
Stretch receptor in bladder – sensory neurone to S2-S4 – ascend up spinal cord – synapses between T10/L2 with sympathetic pre-ganglionic neurone – synapse with post-ganglionic neurones – to the detrusor muscle and IUS = inhibit contraction of detrusor + stim IUS
From the L centre (pons) excitatory neurones – synapse with motor neurones - from S2-S4 = somatic motor neurones (run along pudendal N) = innervates EUS = close
How does the M centre and L centre communicate?
When the M centre is activated = inhibition of L centre + sympathetics = voiding
What receptors are present on the IUS?
Alpha 1
Alpha 1 antagonists = relaxation of IUS = facilitate urination
What receptors in the bladder are inhibitory (storage reflex)?
Beta 3
Beta 3 agonist = inhibit overactive bladder
What receptors in the bladder are involved in the voiding reflex?
M3
What occurs in spinal cord lesions above S2 with regards to micturition?
Loss of inhibition of the stimulatory parasympathetic (voiding) reflex
Bladder overdrive = urination
What occurs in a spinal cord lesion between S2-S4 with regards to micturition?
Can no longer sense that the bladder is full = perpetual storage phase = bladder so big = incontinence
