Neurogenic Bladder: UMN vs LMN: Physiology made easy.

Basic Physiology of Micturition

Micturition is a spinal reflex modulated by CNS.

Neural control of micturition.
Source: http://physiologyplus.com/micturition-reflex-steps/

The pre-frontal cortex is responsible for the cognitive control of the micturition which analyses the signals from bladder and conveys signals according to void or not to void depending on the social setting.

The higher control of micturition is mediated by pontine micturition centre (PMC) from where nerve fibre arise and travel along the lateral columns bilaterally. It is the mechanical control of micturition. It coordinates the function of baldder and sphincter.

The Sympathetic fibres are thoracolumbar (T10-L2) outflow of nerve fibres and terminate in the hypogastric ganglion.

The Parasympathetic fibres are sacral (S2-S4) outflow.

The voluntary control over the external urtheral spincter is mediated by somatic fibres of Pudendal nerve. 

Learn about Cranial nerve examinations

Intact Spinal cord is essential for normal micturition as it serves as a intermediate relay between the brain and the sacral center of micturition. Sacral reflex center is the primitive voiding center which is responsible for infants diaper need, since there is a continuous cycle of bladder filling and voiding. The higher mental function gradually enhances in kids as they are growing and accordingly they are trained to use toilet with their enhanced higher mental function.

	Sympathetic	ParaSympathetic
Bladder (Detrusor Muscle)	Relaxation	Contraction
Bladder Neck	Contarction	Relaxation

The bladder wall is relaxed and the neck constricted with sympathetic stimulation which allows for retention of urine. The parasympathetic stimulation causes bladder wall to contract and sphincter to relax easing the voiding of urine.

Learn about the analogy of skeletal muscle and bladder in UMN and LMN lesions. 

Analogy of Skeletal Muscle contraction and Bladder

LMN vs UMN Lesion : Effect on Bladder

There is a lot of analogy between skeletal muscle contraction and bladder.

In the absence of higher control, overdistension of bladder causes reflex detrusor contraction. Similar to     the muscle stretch reflex mediated by spindle fibre in skeletal muscle.

The upper motor neuron lesion of the brain and the spinal cord causes features similar to that of the UMN lesion of in the muscle characterized by Spastic bladder/ Hypertonic baldder.This is due to the reflex detrusor contraction. There is increased tone of the detrusor muscle. However, the bladder contracts with overdistension, the sphincter does not relax causing bladder sphincter dyssyenrgia. This causes urgency and urge incontinence. The volume of residual urine in the bladder is increased which causes high risk for UTI and chronic renal failure due to obstructive uropathy. The site of the lesion is generally the Spinal cord or pons or higher. There is no gross dilatation of the bladder due to the reflex contraction which results in low volume high pressure inside the bladder.

Learn about the plantar reflexes and its variants with video demonstration

The lower motor neuron lesion to the fibre supplying bladder causes overflow incontinence. This occurs because bladder is overdistended however the reflex detrusor contraction doesnot comes into play. So what happens is the bladder leaks over time when it is beyond its holding capacity without the detrusor muscle contracting. The bladder is grossly dilated resulting in high vomule and low ressure inside the bladder.This can be described as flaccid or atonic bladder similar to flaccid paralysis of muscles in LMN lesion.The patient cannot initiate the micturition. The site of injury is generally the sacral fibres or peripheral nerve fibres

The last type of neurogenic bladder ocuurs due to injury in the prefrontal cortex which is responsible for social control of micturition. It allows us to find us to micturate in appropriate place. The patient doesnot have the sense of bladder fullness. They have trouble initiating micturition and they micturitate at inappropriate places.

Character	UMN Type	LMN Type
	Spastic Bladder	Flaccid Bladder
Tone	Hypertonic (Increased)	Hypotonic (Decreased)
Volume	Normal or small	Large
Detrussor contraction	Involuntary intermittent contractions (Overactiity)	Absent (Underactivity)
Pressure	High	Low
Incontinence type	Urge	Overflow
Symptom	Urgency and Frequency nocturia Leaking of urine	Dribbling of urine Erectile edysfunction in men
Retention	Incomplete bladder voiding (Detrussor-Sphincter Dyssynergia) Uncoordinated bladder contraction and sphincter relaxation	Detrusor Aflexia
Conditions	Spinal Cord damage above T12 Cerebrovascular accidents	Spinal cord damage at S2-S4 Peripheral Nerve injury Acute Stage of spinal cord injury Cauda Equina, Conus medullaris

  

Source: Davidson, Merck’s Manual, Medscape