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SA urinary > S7) Neuronal Control of Micturition > Flashcards

S7) Neuronal Control of Micturition Flashcards

1
Q

What is micturition?

A

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

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2
Q

In 5 steps, describe the basic process of micturition

A

⇒ 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

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3
Q

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

A
  • Provides sensations of bladder (distension & pain)
  • Relaxes bladder
  • Accommodates increasing volume of urine
  • Initiates & maintains voiding (seeing)
  • Regulates of smooth & skeletal muscle sphincters
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4
Q

Briefly, describe the structure and location of the bladder

A
  • Location: situated anteriorly in the pelvic cavity
  • Structure: hollow, highly distensible, rounded in shape
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5
Q

State 2 functions of the bladder

A
  • Temporary storage of urine (~600ml)
  • Assists in the expulsion of urine
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6
Q

The morphological appearance of the bladder varies with filling.

Illustrate this

A
  • When full, it exhibits an oval shape
  • When empty, it is flattened by the overlying intestines
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7
Q

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

Identify these 3 regions

A
  • Apex
  • Neck
  • Body
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8
Q

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

A
  • Urine enters the bladder by the left and right ureters
  • Urine exits via the urethra
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9
Q

The internal urethral orifices are marked by the trigone.

What is this?

A
  • The trigone is a triangular area located within the fundus
  • In contrast to the rest of the internal bladder, it has smooth walls
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10
Q

There are two sphincters controlling the outflow of urine.

Identify them

A
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11
Q

Distinguish between the structure of the male and female IUS (internal urtethral sphincter)

A

- 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
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12
Q

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

A
  • Structure: skeletal muscle, and under voluntary control, this is the spincter we control when we want to wee or hold it in
  • Function: relaxes during micturition to allow urine flow
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13
Q

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

A
  • Structure: specialised smooth muscle, with fibres are orientated in three directions to retain structural integrity when stretched
  • Function: allows bladder contract during micturition
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14
Q

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

A
  • Parasympathetic nervous system (wee)
  • Sympathetic nervous system (not wee)
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15
Q

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

A

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

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16
Q

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

A

M – mucosa

S – submucosa

LP – lamina propria

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17
Q

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

A

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

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18
Q

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

A
  • Somatic nervous system
  • Autonomic nervous system (parasympathetic & sympathetic)
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19
Q

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

Describe the structures involved

A

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

20
Q

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

Describe the structures involved

A

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

21
Q

Somatic nervous system provides voluntary control over micturition.

Describe the structures involved

A

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

22
Q

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

A

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

23
Q

describe the neuronal control over the storage/continence phase of micturition

A
  1. sensory neurone innervated by stretch receptors
  2. Sensory neurone from the bladder enters sacral chord S2-S4
  3. they travel up to T10-12
  4. synapse on sympathetic neurone
  5. tells detrusor muscle to relax and carry on expanding, external sphincter remains closed
24
Q

Which brain centre is responsible for the storage of urine?

A

Pontine storage centre

25
Q

Which sympathetic receptors are involved in the storage phase?

A
  • α1 receptors at the IUS (contracts sphincter)
  • β3 receptors at the detrusor muscle (relaxes bladder)
26
Q

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

A

Noradrenaline

27
Q

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

A
  • sensory neurones (innervated by stretch receptors) enter spinal chord between s2-4
  • synapse with parasympathetic nerves
  • these parasympathetic nerves cause the detrusor muscle to contract and external sphincter to relax
28
Q

Which brain centre is responsible for micturition?

A

Pontine micturition centre

29
Q

Which parasympathetic receptor is involved in the voiding phase?

A

M3 receptors at the detrusor muscle (excited)

30
Q

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

A

Acetylcholine

31
Q

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

A

Sympathetic neurones

32
Q

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

A

Intravesical pressure increases non-appreciably

33
Q

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

A
34
Q

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

A
35
Q

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

A
36
Q

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

A
37
Q

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

A
38
Q

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

A
39
Q

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

A
40
Q

What condition can β3 agonists treat?

A

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

41
Q

What condition can α1 agonists treat?

A

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

42
Q

What condition can M3 antagonists treat?

A

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

43
Q

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

A
  • 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
44
Q

describe the cortical control of storage in the bladder - not reflex

A
  • stretch receptors report to cerebral cortex (sensory neurone)
  • somatic neurones found between S2-4 travel to L centre in brainstem
  • this causes an excitatory effect
  • synapses with pudendal nerve (under conscious control)
  • it closes sphincter and relaxes bladder
45
Q

describe the cortical control of voiding - not reflex

A
  • high levels of bladder stretch
  • sensory neurones enter sacral chord at s2-4
  • send message to M centre (micturition)
  • excitatory message sent to parasympathetic system
  • spinster relax and bladder contracts
46
Q

what is the communication between the l and m centres

A
  • when you want to void then the M centre is activated
  • parasympathetic is activated
  • L centre is inhibited, switches off the pudendal nerve
47
Q

what nerve do babies find hard to control

A
  • they find it hard to store urine
  • so it will be the pudendal nerve they struggle having control over (somatic motor)

SA urinary (25 decks)

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