Lecture 7.1: Neural Control of Micturition Flashcards by Purva Shegunshi

What is Micturition?

Micturition is also known as the voiding phase of bladder control and it is typically a short-lasting event

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What systems are involved in the Neural Control of Micturition

Spinal cord reflex activity
Micturition involves a unique
combination & interaction of autonomic
& voluntary functions

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The ability of voluntary control (inhibition) of the bladder develop?

Develops at the age of 2 – 3 years

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Neural Control of Micturition Pathway

Pressure inside bladder (against walls)
due to urine
Stretch receptor inside detrusor muscle
of bladder detects this
Sensory neurone conducts message to
spinal chord
Then to the Pons
Then to the Cerebral Cortex
Back down spinal chord

Then EITHER:
* Through motor neurone to detrusor
muscle and internal sphincter of
bladder
* Or, a somatic nerve fibre of the
pudendal nerve which innervates the
external sphincter of bladder

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What is Continence?

Continence refers to self-control, it is the ability to hold back bodily functions from the bladder or the bowel

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What is the Effect of the Sympathetic Nervous System on the Bladder? What Spinal Cord Nerves?

Relax Detrusor Muscle
Contract Internal Sphincter
Bladder Holds Urine
Sympathetic T10, L1 & L2

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What is the Effect of the Parasympathetic Nervous System on the Bladder? What Spinal Cord Nerves?

Contracts Detrusor Muscle
Relax Internal Sphincter
Bladder Voids Urine
Parasympathetic S2,S3 & S4, Somatic
neurons S2,S3 & S4

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What are the 2 Phases of Micturition?

Continence Phase
Voiding Phase (Micturition)

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What happens if neuronal pathway of the Continence Phase is damaged?

Damage to this neuronal apparatus will
lead to failure to store urine
Resulting in reduced bladder capacity * Very frequent passing of urine,
commonly referred to as Incontinence

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What happens if neuronal pathway of the Voiding Phase (Micturition) is damaged?

Damage to neurones that promote
micturition will lead to failure to pass
urine voluntarily
Resulting in urinary retention. * Here, urine is only passed by an
overflowing bladder (i.e. involuntary;
overflow incontinence)

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How many ml capacity does the Urinary bladder have?

Around 550 ml (range 300 to 700 ml)

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How many hours does it take to fill the bladder to capacity?

c.9 hours

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What does “high compliance of the bladder” mean?

The ability of the bladder to stretch in
response to an increase in volume of
urine
A physiologically normal bladder has a
relatively constant low bladder pressure
throughout the filling cycle, resulting in
a high compliance

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What is the urinary flow rate in a full bladder in men?

20–25 ml/s in men (lasting around 24s)

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What is the urinary flow rate in a full bladder in women?

25–30 ml/s in women (lasting around 22s)

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General Anatomy of the Urinary Bladder: 3 Main Parts

Body: Temporary store of urine
Trigone: Ureteric orifices & internal
urethral orifice are at angles of a
triangle
Neck: Connects bladder to the urethra

What are the are 3 muscle components of note in the Bladder?

1) Detrusor Muscle (involuntary, smooth)
2) Internal Urethral Sphincter
(involuntary, smooth)
3) External Urethral Sphincter
(formed by pelvic floor muscles)
Somatic, voluntary

Bladder Anatomy Full

Look at Grays Anatomy Flashcards

What are the 3 nerves that directly innervate the Bladder?

Hypogastric (S) Nerve
Pelvic (PS) Nerve
Pudendal (Somatic) Nerve

Hypogastric (S) Nerve: Motor Neurone Target? Pre-ganglionic Neurotransmitter? Post-ganglionic Neurotransmitters?

Sympathetic
Pre-ganglionic Neurotransmitter: ACh
Urethral Smooth Muscle (NE+)
Detrusor (NE-)

Pelvic (PS) Nerve: Motor Neurone Target? Pre-ganglionic Neurotransmitter? Post-ganglionic Neurotransmitters?

Parasympathetic
Pre-ganglionic Neurotransmitter: ACh
Detrusor Muscle (ACh+, ATP+)
Urethral Smooth Muscle (NO-)

Pudendal (Somatic) Nerve: Motor Neurone Target?

Somatic
Pre-ganglionic Neurotransmitter: N/A
Striated Muscle of EUS (ext uri sphi)
Post-ganglionic Neurotransmitter:
ACh+

Detrusor Muscle Structure

It is formed from a plexiform meshwork
of smooth muscle fibres
The layers of the detrusor muscle start
longitudinally in the inner layer
Become circular in the middle layer
Then longitudinal again in the outer
layer

What is the Neural Supply of the Detrusor Muscle Structure?

ANS sympathetic (T10-S2)
Hypogastric nerve & Parasympathetic
(S2-S4) Pelvic nerve

What type of epithelium is the urinary bladder lined with?

Transitional Epithelium

At how many ml do the stretch receptors signal the need to void the bladder?

* 200-400ml * Pain sensation from irritation of bladder * Temperature sensation * Pain sensation in bladder is well localised

Aδ-Fibre Normal Function in Bladder? Myelinated or Unmyelinated? Neurotransmitter(s)?

* Myelinated * Function as mechanorecptors receptors to tension in bladder wall * Transmit sensation of bladder fullness * Glutamate

C-Fibre Normal Function in Bladder? Myelinated or Unmyelinated? Neurotransmitter(s)?

* Unmyelinated * Generally high threshold for mechanical stimuli, function as nocireceptors, responding to chemical irritants and over distention * Small population of C-fibres are mechanosensitive and respond to tension in bladder wall * Glutamate, SP, CGRP

What is another name for the Pontine Micturition Centre (PMC)?

Barrington's Nucleus

Pontine Micturition Centre (PMC) Lateral Region: Function? What does stimulation result in?

* Continence and Urine Storage * Stimulation results in a powerful contraction of the urethral sphincter * Silencing of electrical activity of. Detrusor muscle * Relaxation of the Detrusor muscle (β3- receptors in the fundus and body of the bladder) * Increase in Urethral sphincteric pressure (α-adrenoceptors population in neck)

Pontine Micturition Centre (PMC) Medial Region: Function? What does stimulation result in?

* Micturition Centre * Stimulation results in decrease in urethral pressure and silence of pelvic floor EMG signal, followed by a rise in detrusor pressure

Bilateral Lesions in the Pontine Storage Centre (Lateral Pons) Lead to...?

* An inability to store urine * Reduction in bladder capacity * Excessive Detrusor muscle activity * Relaxation of Urethra * Premature voiding * Leaky bladder (incontinence)

Bilateral Lesions in the Pontine Storage Centre (Medial Pons) Lead to...?

* Dorsomedial Pontine tegmentum is. active during voiding * Also known as the M-region of the pons or Barrington’s nucleus * Bilateral lesions of this region result in severe urinary retention

Mechanical Events During Urinary Continence or Storage

* Walls of the bladder are highly folded, making them distensible * The folds in the bladder are known as rugae * As the bladder fills with urine, Internal urethral sphincter tightens/closes * As the bladder fills with urine, rugae flatten * Stress-relaxation phenomenon * As rugae flatten, capacity of the bladder increases up to 700 ml * As the bladder fills up with urine, intravesical pressure hardly changes

Voiding Circuits- Medial Pons

* Strong contraction of Detrusor muscle * Increase in intravesical pressure (PS- S2-S4- Pelvic nerve) * Relaxation of the Internal Urethral Sphincter (sympathetic T10-L2 Hypogastric nerve) * Voluntary relaxation of the External Urethral Sphincter (Somatic- S2-S4 Pudendal nerve) * Expulsion of Urine