HANDBOOK OF PH\SIOLOGV 



NEUROPHYSIOLOGY II 



and are no longer excited to the point of neuron 

 threshold. Clinical writers are deprived of an ex- 

 planation for this condition (and offer none) because 

 they recognize no descending facilitation. 



The intermediate stage (which ma>' be the final 

 one) of repeated and frequent, althougii small and 

 abortive or partially effective, micturition contrac- 

 tions is paralleled in the return of myotatic skeletal 

 reflexes. They exhibit exactly the same deficiency in 

 being unable to maintain a strong, sustained reflex 

 (e.g. the knee jerk is present when the paraplegic 

 cannot stand), although as with the micturition re- 

 flex, the threshold may be quite low. The end result 

 of a large capacity bladder, as opposed to one with a 

 small capacity, is thus presumed to depend on 

 whether care has pre\entecl those changes in the 

 bladder wall resulting from maintaining the bladder 

 in a state of nearly perpetual, although intermitting, 

 contraction, i.e. unvaried by periodic complete con- 

 tractions and fillings. Thus, the "normal" reflex 

 bladder, or Munro's fourth stage, may be simply a 

 bladder which, through avoidance of shrinkage, is 

 able to operate at the higher volumes, i.e. between 

 the normal and the residual \olume levels. 



Cystitis or the introduction of an irritating solu- 

 tion into the bladder yields a cystometrogram very 

 similar to overreactive neurogenic bladder dysfunc- 

 tion in both man (23; Plum, F., unpublished ob- 

 servations) and animals. This may simply be caused 

 by overacti\ity of the micturition stretch end organs. 

 Another possibility, which should be explored, is 

 that the bladder possesses a second inode of contrac- 

 tion, allied to nociceptive somatic reflexes which are 

 fasored in the spinal state and which are phasic 

 rather than sustained. Such nociceptive reflexes 

 could be operatise in l)oth cystitis and after spinal 

 cord lesions. 



.AUTONOMOUS NEUROGENIC BLADDER. SYNONOMY : IN- 

 FRANUCLEAR NEUROGENIC BLADDER DYSFUNCTION, 

 DECENTR.^LIZED BL.'KDDER, DENERVATED BL.ADDER. 



This category is well named since remaining bladder 

 function is carried on only by the bladder and the 

 outlying plexus because both the afferent and the 

 efferent parasympathetic limbs of the reflex arc are 

 interrupted by blockade or destruction of the conus 

 meduUaris, the cauda equina, the sacral ner\'e roots, 

 the pelvic nerve or the inferior hypogastric plexus. 

 The terminology assumes that the sympathetic in- 

 nervation plays no part in the micturition reflex. 



Bladder sensation and voluntary and spinal re- 

 flex micturition are abolished; the remaining con- 



tractions, if any, are small in amplitude, although 

 some authors (9) have reported quite vigorous con- 

 tractions. The bladder capacity is initially large but 

 returns to or below normal, intravesical pressure is 

 high and small micturitions are frequent. Denny- 

 Brown & Robertson (8) ascribed a consideralile part 

 of the activity of the ijladder to the intramural 

 plexus, whereas McLellan (20) discounts it. Car- 

 penter & Root (5) recorded autonomous contrac- 

 tions attaining 54 cm hydrostatic pressure, i.e. at 

 the lower range of normal micturition pressures. The 

 cystometrogram is likely to show a steeply ascending 

 tonus limb, the basis of which has been di.scussed 

 previously. How the physiology of the intramural 

 plexus effects vesical contraction, e.g. whether by 

 axon reflexes or by a synaptic connection between 

 sense organ and postganglionic effectors, has received 

 little attention. The contractions occur after pelvic 

 nerve section and degeneration of most of the af- 

 ferent supply to the bladder, a fact which argues 

 against axon reflexes of one type. Contractions do 

 not occur after sacral posterior root section; they may 

 be myogenic. 



TABETIC BLADDER. SYNONOMY: ATONIC NEUROGENIC 



BLADDER. An interruption of the sacral posterior roots 

 leaving the motor roots intact completely abolishes 

 the desire to micturate, although a vague awareness 

 of bladder fullness may persist. Reffex contraction of 

 the detrusor muscle iails, and there is a high residual 

 overffow incontinence and a thinning rather than a 

 hypertrophy of the bladder wall. No satisfactory ex- 

 planation for the absence of activity in the intra- 

 mural plexus has been evolved. The state is com- 

 parable to the absence of the skeletal myotatic 

 reflexes when their posterior root inner\ation is de- 

 stroyed. The atonia, as we have seen, is secondary 

 to the failure of the micturition reflex and results 

 from oserdistention. 



CONTROL OF BLADDER SPHINCTERS 



The act of micturition in\ol\es an interplay of the 

 detrusor muscle, the internal sphincter, the external 

 sphincter (striate muscle), and striate accessory 

 muscles of the abdominal wall and the pelvic floor. 



The internal sphincter is not an anatomical 

 sphincter in the sense of Lieing a distinct, circularly 

 arranged, smooth muscle. Rather, it is a 'physiologi- 

 cal sphincter" composed of extensions of the trigonal 

 and mural musculature, sweeping o\er and under 



