Lecture 7.1: Neural Control of Micturition Flashcards
What is Micturition?
Micturition is also known as the voiding phase of bladder control and it is typically a short-lasting event
What systems are involved in the Neural Control of Micturition
- Spinal cord reflex activity
- Micturition involves a unique
combination & interaction of autonomic
& voluntary functions
The ability of voluntary control (inhibition) of the bladder develop?
Develops at the age of 2 – 3 years
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
What is Continence?
Continence refers to self-control, it is the ability to hold back bodily functions from the bladder or the bowel
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
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
What are the 2 Phases of Micturition?
- Continence Phase
- Voiding Phase (Micturition)
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
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)
How many ml capacity does the Urinary bladder have?
Around 550 ml (range 300 to 700 ml)
How many hours does it take to fill the bladder to capacity?
c.9 hours
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
What is the urinary flow rate in a full bladder in men?
20–25 ml/s in men (lasting around 24s)
What is the urinary flow rate in a full bladder in women?
25–30 ml/s in women (lasting around 22s)
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
