S7) Neuronal Control of Micturition

Question 1

What is micturition?

Answer 1

Micturition is the release of urine from the urinary bladder through the urethra to the outside of the body (urination)

Question 2

In 5 steps, describe the basic process of micturition

Answer 2

⇒ Urine is made in the kidney

⇒ Urine is stored in the bladder

⇒ Sphincter muscles relax

⇒ Detrusor muscle contracts

⇒ Bladder is emptied through urethra & urine is excreted

Question 3

Identify 5 functions of the nervous system in relation to the lower urinary tract

Answer 3

• Provides sensations of bladder (distension & pain)
• Relaxes bladder
• Accommodates increasing volume of urine
• Initiates & maintains voiding
• Regulates of smooth & skeletal muscle sphincters

Question 4

Briefly, describe the structure and location of the bladder

Answer 4

• Location: situated anteriorly in the pelvic cavity
• Structure: hollow, highly distensible, rounded in shape

Question 5

State 2 functions of the bladder

Answer 5

• Temporary storage of urine (~600ml)
• Assists in the expulsion of urine

Question 6

The morphological appearance of the bladder varies with filling.

Illustrate this

Answer 6

• When full, it exhibits an oval shape
• When empty, it is flattened by the overlying intestines

Question 7

The bladder has 3 major functional muscular units that play a critical role in normal functions.

Identify these 3 regions

Answer 7

• Apex
• Neck
• Body

Question 8

Describe the entry and exit of urine in relation to the bladder

Answer 8

• Urine enters the bladder by the left and right ureters
• Urine exits via the urethra

Question 9

The internal urethral orifices are marked by the trigone.

What is this?

Answer 9

• The trigone is a triangular area located within the fundus
• In contrast to the rest of the internal bladder, it has smooth walls

Question 10

There are two sphincters controlling the outflow of urine.

Identify them

Answer 10

Question 11

Distinguish between the structure of the male and female IUS

Answer 11

- Male IUS consists of circular smooth fibres, which are under autonomic control

• Female IUS has no sphincteric muscle present and is formed by the anatomy of the bladder neck and proximal urethra

Question 12

The external urethral sphincter has the same structure in both sexes, hence, describe its structure and function

Answer 12

• Structure: skeletal muscle, and under voluntary control
• Function: relaxes during micturition to allow urine flow

Question 13

Describe the structure and function of the detrusor muscle in the bladder wall

Answer 13

• Structure: specialised smooth muscle, with fibres are orientated in three directions to retain structural integrity when stretched
• Function: allows bladder contract during micturition

Question 14

Which divisions of the nervous system innervate the detrusor muscle during micturition?

Answer 14

• Parasympathetic nervous system
• Sympathetic nervous system

Question 15

Where along the extent of the urinary system is the following image from?

Answer 15

Trigone – only location in the bladder where the detrusor muscle consists of three layers

Question 16

Name the structres M, S, LP shown in the photomicrograph below

Answer 16

M – mucosa

S – submucosa

LP – lamina propria

Question 17

Which muscle composes layers 1,2,3 shown in the photomicrograph below?

Answer 17

Detrusor muscle – fibres oriented in 3 different directions in area of trigone

Question 18

Identify which divisions of the nervous system provide innervation to the bladder

Answer 18

• Somatic nervous system
• Autonomic nervous system (parasympathetic & sympathetic)

Question 19

The sympathetic innervation of the bladder promotes urine retention (continence).

Describe the structures involved

Answer 19

SNS communicates with the bladder via the hypogastric nerve (T12 – L2), causing the relaxation of the detrusor muscle

Question 20

The parasympathetic innervation of the bladder stimulates voiding (micturition).

Describe the structures involved

Answer 20

PNS communicates with the bladder via the pelvic nerve (S2-S4), causing the contraction of the detrusor muscle

Question 21

Somatic nervous system provides voluntary control over micturition.

Describe the structures involved

Answer 21

Somatic innervates the external urethral sphincter via the pudendal nerve (S2-S4) to constrict (storage phase) or relax (voiding phase) it

Question 22

Where are the sensory (afferent) nerves located and what do they do?

Answer 22

Afferent fibres of the pelvic nerve are found in the bladder wall and convey sensory information (distension & pain) to the brain

Question 23

In 3 steps, describe the neuronal control over the storage/continence phase of micturition

Answer 23

Question 24

Which brain centre is responsible for the storage of urine?

Answer 24

Pontine storage centre

Question 25

Which sympathetic receptors are involved in the storage phase?

Answer 25

- **α1 receptors** at the IUS (contracts sphincter) - **β₃ receptors** at the detrusor muscle (relaxes bladder)

Question 26

What is the postganglionic neurotransmitter for the sympathetic receptors in the storage phase?

Answer 26

Noradrenaline

Question 27

In 5 steps, describe the neuronal control over the voiding phase of micturition

Answer 27

Question 28

Which brain centre is responsible for micturition?

Answer 28

Pontine micturition centre

Question 29

Which parasympathetic receptor is involved in the voiding phase?

Answer 29

M₃ receptors at the detrusor muscle (excited)

Question 30

What is the postganglionic neurotransmitter for the parasympathetic receptor in the voiding phase?

Answer 30

Acetylcholine

Question 31

What type of neurones in the spinal cord exclusively mediate continence?

Answer 31

Sympathetic neurones

Question 32

In the continence phase, as the bladder enlarges what happens to intravesical pressure?

Answer 32

Intravesical pressure increases non-appreciably

Question 33

Identify structures 1-4 in the coronal section of the male bladder below:

Answer 33

Question 34

Identify structures 5-9 in the coronal section of the male bladder below:

Answer 34

Question 35

Identify structures 1-4 in the posterior view of the male bladder below:

Answer 35

Question 36

Identify structures 5-7 in the posterior view of the male bladder below:

Answer 36

Question 37

Identify structures 1-4 in the coronal section of the female bladder below:

Answer 37

Question 38

Identify structures 5-8 in the coronal section of the female bladder below:

Answer 38

Question 39

Identify structures 9-11 in the coronal section of the female bladder below:

Answer 39

Question 40

What condition can β3 agonists treat?

Answer 40

**β3 agonists** can treat an **overactive bladder** as they act at the β3 receptors to relax the bladder (sympathetic)

Question 41

What condition can α1 agonists treat?

Answer 41

**α1 agonists** treat lower urinary tract symptoms such as **incontinence** as they act at the α1 receptors to contract the IUS (sympathetic)

Question 42

What condition can M3 antagonists treat?

Answer 42

M3 antagonists can treat **urinary incontinence** as they inhibit bladder contraction to promote urinary retention

Question 43

What is the impact of spinal cord lesions from T5-T10?

Answer 43

- Spinal cord lesions destroy inhibitory inputs but not parasympathetic fibres so **bladder is overactive** - Sympathetics keep sphincters closed so pressure increases and **muscle** and **sphincter thicken**