Different neurological disorders affect the gastrointestinal tract in different ways: Spinal cord injury<unk><unk>  caused by a spinal cord injury will vary greatly depending on the severity and level of the spinal cord lesion. In complete spinal cord injury both sensory and motor functions are completely lost below the level of the lesion so there is a loss of voluntary control and loss of sensation of the need to defecate. An incomplete spinal cord injury is one where there may still be some sensation or motor function below the level of the lesion. Colorectal<unk>  due to spinal cord injury can be classified in to two types: an upper motor neuron lesion or lower motor neuron lesion. Problems with the upper motor neuron in a<unk><unk>  results in a hypertonic and spastic<unk>  because the defecation reflex centre, which causes the involuntary contraction of muscles of the rectum and anus, remains intact. However, the nerve damage results in disruption to the nerve signals and therefore there is an inability to relax the anal sphincters and defecate, often leading to constipation. An upper motor neuron lesion is one that is above the conus medullaris of the spinal cord and therefore above the vertebral level T12. On the other hand, a lower motor neuron lesion can cause areflexia and a flaccid external anal sphincter so most commonly leading to incontinence. Lower motor neuron lesions are damage to nerves that are at the level of or below the conus medullaris and below vertebral level T12. However, both upper and lower motor neuron disorders can lead to constipation and/ or incontinence. Spina bifida Patients with Spina Bifida have a neural tube that has failed to completely form. This is most commonly in the lower back area in the region of the conus medullaris or cauda equina. It, therefore, affects the<unk>  similarly to a spinal cord injury affecting the lower motor neuron resulting in a flaccid unreactive rectal wall and means the anal sphincter doesn't contract and close therefore leading to stool leakage. Most patients with spina bifida also have hydrocephalus this can result in intellectual deficits so can contribute to faecal incontinence. Multiple sclerosis There are a variety of symptoms associated with this condition that are all caused by a loss of myelin, the insulating layer surrounding the neurones. This means the nerve signals are interrupted and slower which will then cause muscle contractions to be fewer and irregular resulting in an increased colon transit time. The faeces being in the colon for a longer time will mean that more water is absorbed leading to harder stools and therefore increasing the symptoms of constipation. This neurological problem can also lead to reduced sensation of rectal filling and weakness of the anal sphincter because of weak muscular contraction so can cause stool leakage. In patients with multiple sclerosis constipation and faecal incontinence often coexist and they can be acute, chronic or intermittent due to the fluctuating pattern of MS. Brain lesion Damage to the defecation centre within the medulla oblongata of the brain can lead to<unk><unk> . A stroke or acquired brain injury may lead to damage to this centre in the brain. Damage to the defecation centre can lead to a loss of coordination between rectal and anal contractions and also a loss of awareness of the need to defecate. Parkinson's disease This condition differs as it affects both the extrinsic and enteric nervous systems due to the decreased dopamine levels in both. This results in less smooth muscle contraction of the colon, increasing the colon transit time. The reduced dopamine levels also causes dystonia of the striated muscles of the pelvic floor and external anal sphincter. This explains how Parkinson's disease can lead to constipation. Diabetes mellitus Twenty percent of people with diabetes mellitus experience faecal incontinence due to irreversible autonomic neuropathy. This is due to the high blood glucose levels over time damaging the nerves, which can lead to impaired rectal sensation.
Neurogenic bowel dysfunction
Functional constipation
Obstructed defecation
Sphincter of Oddi dysfunction
Sphincter paralysis
Rectal foreign body
Athletic incontinence
Rectal prolapse