Neural Control of Micturition

Question 1

What type of control is micturition

Answer 1

Autonomic and Voluntary

Question 2

How can micturition be described?

Answer 2

a spinal reflex that is inhibited or facilitaed by higher brain centres

Question 3

What are the bladders two modes

Answer 3

storage and elimination

Question 4

what is the shape of the bladder

Answer 4

triangular pyramid shape

1 base, 1 superior and 2 inferolateral sides

Question 5

which muscles control micturition (4)

Answer 5

Detrusor (bladder wall)

Internal urethral sphincter

External urethral sphincter

Bulbospongiosus (gets last bit out of the pipe)

Question 6

what is the capacity of the bladder

Answer 6

500ml

1st voiding urge at 150ml

fullness felt at 400ml

Question 7

What does the PMC (pontine micturition centre) do

Answer 7

acts as a relay station for ascending spinal bladder information (from stretch mechanoreceptors)

neuronal silence = bladder empty

to urinate relaxes external urethral sphincter while contracting of the detrusor muscles

Question 8

What does the PAG (periaqueductal grey) do

Answer 8

acts as important sensory & motor relay station

Question 9

What is amnion fluid made of

Answer 9

mostly urine and small extent from lungs

Question 10

what are uterus conditions like for the foetus

Answer 10

8 months drinking urine/faeces & inhaling

insufficient urine under develops the lungs & can cause contractures & club feet

Question 11

what happens to the lungs during pseudo glandular phase

Answer 11

formation of bronchial tree to terminal bronchioles

Broncho-pulmonary epithelium begins to produce amniotic fluid

Question 12

what happens if the foetus stops urinating

Answer 12

renal agenesis - can be fatal baby will be born with 1 or no kidneys

less amnion fluid means only the placenta is keeping them alive

Question 13

How does the involuntary micturition reflex work

Answer 13

stretch receptors detect full bladder

efferent signals returned from spinal cord S2/S3 excite detrusor muscles

and relax internal urethral sphincter

if not inhibited by the brain urine will be voided

Question 14

what can trigger micturition reflex voiding?

Answer 14

suprapubic percussions

thigh scratching

touching penile skin

pulling pubic hair

Question 15

how does voluntary control of micturition work?

Answer 15

stretch receptors signal

if it is not time to urinate cerebrum excites spinal interneurons to keep external sphincter contracted

when it is time cerebrum inhibits sacral neurons that keep the sphincter closed

Question 16

why do babies wet the bed?

Answer 16

stretch sensory information from the bladder doesn’t wake the baby

brain doesn’t not inhibit the external sphincter so automatic reflex takes place

Question 17

Why is hard to urinate with an a erection?

Answer 17

parasympathetic nerves allow urination and erection but cannot be done at same time

prevents urination during intercourse

during ejaculation (sympathetic) pressure in the urethra over-powers the corpus spongiosum

Question 18

how does ejaculation occur

Answer 18

sympathetic nerves cause the following

detrusor muscles relax

contracts internal urethral sphincter

pudendal nerve contracts the bulbocavernosus muscle

net result: prevents semen escaping into bladder

Question 19

what happens to cause an autonomous bladder

Answer 19

the loss of sacral nerves (parasympathetic & pudendal)

sympathetic nerve remains unopposed causing detrusor to relax and internal sphincter to contract causing backfill

Question 20

what causes atonic bladder

Answer 20

when spinal cord is damaged (lasts days-weeks) detrusor muscles relax and internal sphincter contracts - urine is retained and patient may not realise

Question 21

how does dementia effect micturition

Answer 21

50% of nursing home patients have bladder control issues

difficulty of cerebrum interpretation

harder to find toilet and hold it in while doing so

apraxia - difficulty undressing/using toilet