Micturition

Question 1

Micturition

Answer 1

-voluntary control of voiding the bladder (urination)

Question 2

Detrusor muscle

Answer 2

-smooth muscle covering the bladder
=parasympathetic and sympathetic innervation

Question 3

Detrusor muscle order of signals

Answer 3

-stretch receptors on smooth muscle of bladder innervated by the sensory arm
- sensory arm will send signal and synapse on interneuron in the spinal cord when there is a detect of stretch/bladder filling
-Interneuron synapses on another interneuron that travels up and synapses on the pons (pontine micturition center)
-interneuron between pons and another interneuron that sends signal down to parasympathetic motor neurons/motor arm
-Motor neuron has a pre-ganglionic motor neuron and a post-ganglionic motor neuron which will cause contraction of the bladder

Question 4

Which spinal segments are linked to the urethralis muscle?

Answer 4

-S1, S2, S3

Question 5

How does animal have ability to prevent urination when a stretch reflex occurs?

Answer 5

-Detrusor muscle has detected stretch and sent signals resulting in signal to contract
>Now, need to have some sort of voluntary control so that animal can hold urination= NOT through detrusor (smooth muscle)… need Urethralis muscle (skeletal muscle)

Question 6

Urinary sphincter control

Answer 6

-involuntary/unconscious control through reflex arc
>skeletal muscle=urethralis muscle which blocks flow of urine out of urethra (acts like sphincter).
>When stretch detected due to contraction/fill of detrusor muscle, urethralis muscle will also contract and close off exit

Question 7

Which spinal segments, sensory/motor neurons are linked with urethralis muscle?

Answer 7

-S1, S2, S3
-Pudendal nerve

Question 8

Phases of micturition

Answer 8

1.storage (retention of urine)
2.elimination (voiding of bladder)

Question 9

Voluntary bladder control

Answer 9

-Now animal needs to be able to choose when to eliminate urine
-descending UMNs from the cortex that synapse on the pontine micturition center AND the reflex arc that controls the urethralis muscle
*UMNs can be excitatory or inhibitory (elimination vs. storage phases)
1.UMN to the pons will inhibit the contraction of the detrusor muscle, allowing it to fill without contraction. Urethralis muscle will continue constriction to keep urine inside and allow bladder to fill.
2. At the point when bladder is very full and animal is in location where they can void their bladder, UMN to the pons will be excitatory, telling detrusor to contract and push urine out. At the same time the UMN to the urethralis muscle will be inhibitory telling the muscle to relax and allow voiding of urine

Question 10

Sympathetic hypogastric nerve (T12-L3) innervation

Answer 10

**all about activating storage phase
-come down from spinal cord (pre-ganglionic and post-ganglionic) that affect detrusor and urethalis muscle
-sympathetic neurons release NE (alpha at urethalis, beta is at detrusor)
>Detrusor relaxes
>urethralis contracts

Question 11

Blocked cats

Answer 11

-drugs target alpha= alpha 1 blockers
>this will decrease urethralis constriction

Question 12

Leaky bladder

Answer 12

-results from weak urethralis
-drugs=alpha agonists which encourage urethralis constriction increasing sympathetic control
>prevents urinary incontinence

Question 13

Cortical lesions affecting micturition

Answer 13

-cause lack of voluntary urinary control
-loss of inhibition of detrusor muscle resulting in constriction of the detrusor muscle
-no inhibition occurring so promote tone on urethralis muscle=increased constriction
>need to be careful expressing bladder because possible to rupture due to pressure
=UMN bladder

Question 14

Lesion in the pons or spinal cord

Answer 14

-pons-L7 damage will result in damage to reflex segment of the detrusor muscle
>no signal for the bladder to contract, results in infinite filling.
-Increased urethralis muscle contraction (due to detection of increased stretch) because this reflex arc not affected
=UMN bladder

Question 15

Lesions of the sacral area

Answer 15

-damage to S1, S2, S3 or damage to the pudendal or the pelvic nerve =results in LMN damage and therefore a decrease in reflex
>inability for reflex arc to activate so urethralis muscle will not contract (decreased tone) which means as the bladder fills, the urine will passively flow out of the urethra= LMN bladder
**detrusor activates as normal, stretch reflex occurs and fills (although bladder never truly fills because the urine is always passively leaking so animal never feels they need to urinate) but will never stretch out enough to activate contraction

Question 16

Types of bladders

Answer 16

-LMN bladder: flaccid bladder, easy to express, leaky because no urethral tone
-UMN bladders: large, firm, difficult to express. Will have some leaking due to overflow