Which vertebrae’s nerves connect to the lower digestive track. And at what point is the line between SOME (wear undies) and NO (wear diapers) be?
There’s a fuzzy line around T-12 for complete SCI. Above that there is more muscle tone in the bladder and bowels, including the sphincters. Below that and the muscles are more flaccid.
Either way affects urinary incontinence. Higher injuries can result in a spastic bladder which can be damaging if the sphincters hold it in, or incontinence if they don’t. Lower injuries can result in a flaccid bladder as well as flaccid sphincters, again causing incontinence. Incontinence can be controlled by bladder catheterization, or by possibly an external condom catheter for a man.
The bowel is controlled by the gut’s own nervous system, but the sphincters are partly reflex and partly controlled by the brain. Upper injuries can cause spastic sphincters as well, and lead to severe constipation. Fiber and laxatives can counteract it, but if you take too much it results in incontinence. Flaccid sphincters from lower injuries can also cause incontinence.
Strangely, the gut’s nervous system can be trained to go at a chosen time of day but incontinence is still possible. The overall effects of SCI are personally very variable, and can also change over time.
Am I missing something, or are the words "above and “below” being used in some special way? Because I don’t understand how an injury higher on the spinal cord can result in less loss of muscle tone.
To the person wondering, “Above”= closer to head, “Below”= closer to legs (I assume) I’m disabled, so I SHOULD know that!
IANAD but my understanding is there are neurons coming from the brain to each level of spinal cord roots that are called the upper motor neurons. They activate the lower motor neurons that travel from the spinal cord out to the muscles. Injuries to the upper motor neurons above a point of interest tend to result in spastic firings of the lower motor neurons at and below the point of interest. The firings can be fast enough to create always or partly clenched muscles.
In addition, spinal cord sections below the injury have an intact reflex arc, which means that sensory signals coming from the muscles can also activate the lower motor neurons for those muscles.
Injuries to the lower motor neurons cause muscles under their control to be flaccid. The muscles of the bladder and its sphincters, and the rectal sphincter, are controlled by the lumbar and sacral areas of the spinal cord. Thus, injuries above T-12 are all upper motor neuron injuries for the bladder and rectum, and injuries below T-12 are a mixture of types.