control of micturition

define micturition

normsl process of passive storage and active voiding of urine

what type of movement along the ureters to move urine takes place?

• peristalsis

what muscle is involved in urine passage?

• smooth muscle

what type of pressure needs to be maintained in the renal pelvis for urine flow to take place?

• low pressure

what prevents retrograde flow back into the kidney?

• oblique angle of the ureter entry in the bladder wall

what control is storage and voiding under?

• neurological

what muscle do we find:

• bladder

• urethra

1. smooth muscle

2. smooth muscle, skeletal muscle

what is the muscle of the bladder called?

• detrusor muscle

what type of muscle is the detrusor?

• smooth

what innervation does the detrusor muscle have?

• SNS

  • PSNS

what is the internal uretharal sphincter?

• a thickening of the bladder musculature

what type of muscle makes up the internal urethral sphincter?

• smooth muscle

what innervation does the internal urethral sphincter have?

• sympathetic

what is the external urethral sphincter made of?

• striated muscle fibres

what nervous control is the external urethral sphincter under?

• voluntary control of somatic nervous system

what innervation is involved iin the bladder?

• sensory and motor

what sensory input is involved in micturition?

• stretch sensitive nerve fibres ending in the bladder wall

what responds to motor innervation in the bladder?

• detrusor muscle

what levels of innervation are involved in micturition?

• motor - somatic, PSNS, SNS

• sensory

Somatic motor supply:

• outflow from where

• nerve?

• synapse?

• innervates?

• function?

1. S1-2

2. pudendal nerve

3. none

4. urethral skeletal muscle - external urethral sphincter

5. retain urine

PSNS to bladder:

1. outflow from where

2. plexus?

3. synapses?

4. innervates?

5. neurotransmitter?

6. action?

7. function?

1. S1-3

2. pelvic

3. pelvic plexus or bladder wall

4. detrusor muscle

5. ACh

6. excitatory

7. empty bladder

SNS supply: to detrusor muscle

1. outflow from where?

2. synpases?

3. neurotransmitter

4. receptor

5. action

6. function

1. L1-4

2. caudal mesenteric ganglion/bladder wall

3. NE

4. beta

5. inhibitory

6. allows bladder filling

SNS to internal sphincter:

1. Outflow?

2. synapse?

3. innervates?

4. neurotransmitter

5. receptor?

6. action?

7. function?

1. L1-4

2. caudal mesenteric ganglion

3. internal sphincter

4. NE

5. alpha

6. excitatory

7. retain urine, increase urethral tone

what is the overall function of the sympathetic and somatic innervation?

• retain urine

what is the overall function of the PSNS innervation of the bladder?

• voidation

What are each of the colours?

• red = sympathetic

• blue = sensory

• green = parasympathetic

• dark blue = somatic

what are the central connections of micturition?

• control at level of pons and cerebral cortex

• some postulated control from the cerebellum

what reflex is involved in micturition?

• detrusor reflex

what is the detrusor reflex?

• increased vesicular P with filling achieves threshold → contraction of detrusor muscle

what does the detrusor reflex result in?

• contraction against urethral sphincter tone

what is the micturition reflex?

• detrusor reflex + inhibition of sympathetic and voluntary motor supply to bladder and urethra

what feedback loop does the detrusor reflex have?

• positive - will continue until bladder is fully emptied

what are the 2 controls of micturiton

• automatic (detrusor reflex)

• voluntary control (relaxation of external urinary sphincter

can micturition ever be an entirely voluntary process?

• no - once overfilled, intact bladder will empty automatically

what drug could we use to decrease sphincter tone?

• alpha-adrenergic blocker e.g. phenozybenzamine

given an example drug we can use to increase sphincter tone

• alpha-sympathomimetic e.g. phenylpropanolamine

which part of the nervous system do a-adrenergic blockers and a-sympathomimetics target?

• sympathetic

given an example of how we can use the somatic nervous system to aid micturition

• skeletal muscle relaxant - decrease sphincter tone

given an example of how we can use the PSNS to affect micturition

• parasympathomimetic e.g. bethanecol

• increases detrusor tone