Lecture 7.1: Neural Control of Micturition

Question 1

What is Micturition?

Answer 1

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

Question 2

What systems are involved in the Neural Control of Micturition

Answer 2

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

Question 3

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

Answer 3

Develops at the age of 2 – 3 years

Question 4

Neural Control of Micturition Pathway

Answer 4

• 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

Question 5

What is Continence?

Answer 5

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

Question 8

What are the 2 Phases of Micturition?

Answer 8

• Continence Phase
• Voiding Phase (Micturition)

Question 9

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

Answer 9

• 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

Question 10

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

Answer 10

• 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)

Question 11

How many ml capacity does the Urinary bladder have?

Answer 11

Around 550 ml (range 300 to 700 ml)

Question 12

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

Answer 12

c.9 hours

Question 13

What does “high compliance of the bladder” mean?

Answer 13

• 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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

General Anatomy of the Urinary Bladder: 3 Main Parts

Answer 16

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

Question 17

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

Answer 17

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

Question 18

Bladder Anatomy Full

Answer 18

Look at Grays Anatomy Flashcards

Question 19

What are the 3 nerves that directly innervate the Bladder?

Answer 19

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

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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

Question 22

Pudendal (Somatic) Nerve: Motor Neurone Target?

Answer 22

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

Question 23

Detrusor Muscle Structure

Answer 23

• 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

Question 24

What is the Neural Supply of the Detrusor Muscle Structure?

Answer 24

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

Question 25

What type of epithelium is the urinary bladder lined with?

Answer 25

Transitional Epithelium

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

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

Answer 28

• 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

Question 29

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

Answer 29

Barrington’s Nucleus

Question 30

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

Answer 30

• 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)

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

• 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

Question 34

Mechanical Events During Urinary Continence or Storage

Answer 34

• 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

Question 35

Voiding Circuits- Medial Pons

Answer 35

• 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