Urinary Bladder and Clinical Correlates

Hello everyone! This write-up attempts to organize the seemingly confusing nerve supply of the bladder and associated pathology aka the neurogenic bladder.

NERVE SUPPLY :

(beta 2 and alpha 1 are adrenergic receptors of SANS ; muscarinic type 3 is a cholinergic receptor of PANS)

• SANS inhibits micturition while PANS facilitates micturition. You don’t want to pee when you’re running a 100m sprint, an SANS-dominant activity but you can comfortably pee at rest, a PANS-dominant activity.

• Sensory fibres of pudendal nerve tell your CNS when the bladder is full. The motor fibres of pudendal nerve maintain EUS tonic contraction by default so that you’re not always peeing.

• The reflex arc, after higher centre commands, causes voluntary micturition by inhibiting the “contraction-effect” of motor fibres of pudendal nerve.

•  To oversimplify matter (so that it’s easy to understand and remember): Level 2 control inhibits reflex arc. Level 3 control facilitates reflex arc, causing micturition at will, once the bladder is full.

CLINICAL CORRELATES:

• CORTICAL BLADDER

-- Aka Incomplete Spastic OR Uninhibited bladder.

LESION	CLINICAL  FEATURE
Postcentral cortex	--  Loss of awareness of bladder fullness          --  Incontinence
Precentral cortex	--  Hesitancy = Difficulty in initiating micturition
Frontal cortex	--  Precipitancy = micturition with ‘easy’ stimulus, eg: sound of running water          -- Inappropriate micturition/ loss of social inhibition (infant-like)

Associated with:

Multiple Sclerosis

Parkinson’s disease

Stroke, among others.

• HYPERTONIC/ AUTOMATIC  BLADDER

-- UMNL/ Complete spastic type of bladder.

LESION	CLINICAL  FEATURE
Spinal cord ABOVE S2, S3 and S4.	--  Urge incontinence = patient passes low-volume urine frequently         --  Less post-voidal urine volume, so less risk of UTIs         --   More intra-vesical pressure, more risk reflux nephropathy

• HYPOTONIC/ AUTONOMOUS BLADDER

-- LMNL/ Flaccid type of bladder.

LESION	CLINICAL FEATURE
--  Spinal cord AT S2, S3, S4         --  Cauda equina/ Conus medullaris         --   Peripheral nerves	--  Overflow incontinence =  urine retention, overtime, forces IUS to mechanically open causing dribbling micturition         --  More post-voidal urine volume, more risk UTIs

2 subtypes are:

• Motor Paralytic bladder – Motor (efferent) pathway is damaged. However, patient can sense bladder fullness, resulting in prompt diagnosis. Associated with:

--  Complication of abdominal/ pelvic surgery

--  Lumbar canal stenosis

--  Lumbo-sacral meningo-myelocele

• Sensory Paralytic bladder – Sensory (afferent) pathway is damaged and hence, patient canNOT sense bladder fullness, resulting in delayed diagnosis. Associated with:

--  Diabetes mellitus

--  Syringomyelia

--  Tabes dorsalis

Medicine pearl: When we talk about bladder pathology, we only refer to PANS (lesions above/ at/ below it) as SANS lesions doNOT cause bladder pathology per se. However, bilateral lesion to L1 causes retrograde ejaculation and hence, infertility.

Topics for further reading:

--  Age-related urine continence

--  Nocturnal enuresis

--  Barrington reflexes

Hope this helps! Let me know if anything needs clarification. Happy studying!

-- Ashish Singh.