Spinal mechanisms contributing to urethral striated sphincter control during continence and micturition: "how good things might go bad".

The external urethral sphincter motoneurons in the sacral ventral horn control the striated external urethral sphincter muscles that circle the urethra. Activity in these motoneurons and muscle normally contribute to continence but during micturition, when urine must pass through the urethra, the motoneurons and striated muscle must be silenced. Following injury to descending pathways in the spinal cord, the ability to inhibit sphincter activity is disrupted or lost, resulting in bladder-sphincter dyssynergia and functional obstruction of the urethra during voiding.

Plateau potentials and membrane oscillations in parasympathetic preganglionic neurones and intermediolateral neurones in the rat lumbosacral spinal cord.

Whole-cell patch recordings were made from parasympathetic preganglionic neurones (P-PGNs) and unidentified intermediolateral (IML) neurones in thick slices of the lower lumbar and sacral spinal cord of 14- to 21-day-old rats. The P-PGNs and IML neurones examined were similar in terms of soma sizes, input resistance and capacitance, and displayed a sag conductance as well as rebound firing. In the absence of drugs, the neurones responded with either tonic or adapting firing to depolarizing current steps.

Sacral dorsal horn neurone activity during micturition in the cat.

The excitability of two groups of neurones located in different parts of the sacral spinal cord were examined during micturition in decerebrate adult cats. One group of cells, characterized by their activation by pudendal cutaneous afferents, was located in the dorsal commissure of the first and second sacral spinal segments. The second group, located in the dorsal horn of the first sacral spinal segment, was excited by group II muscle and cutaneous afferents.

Spinal cord neural organization controlling the urinary bladder and striated sphincter.

The storage and elimination of urine requires the coordination of activity between the autonomic nervous system (thoracolumbar sympathetic and sacral parasympathetic divisions) controlling the urinary bladder and urethra and the lumbosacral somatic motoneurons innervating the striated sphincter and pelvic floor muscles. These three efferent systems involved in the control of lower urinary tract function receive segmental sensory information from various visceral organs and the perineum, as well as inputs from supraspinal regions. Ascending and descending connections between the various spinal segments levels and supraspinal regions provide the reflex substrates participating in normal bladder continence and micturition reflexes.

Sacral spinal interneurones and the control of urinary bladder and urethral striated sphincter muscle function.

Normally, during bladder filling (continence) and expulsion (micturition) there is a reciprocity between the pattern of activity in the urinary bladder sacral parasympathetic efferents and the somatic motoneurones innervating the striated external urethral sphincter muscle. The co-ordination of this pattern of reciprocal activity appears to be determined by excitatory and inhibitory actions of a variety of segmental afferents and descending systems with sacral spinal actions. These actions may in part be mediated through lower lumbar and sacral excitatory and inhibitory spinal interneurones.