The cerebral cortex is composed of gray matter which consists of the nuclei of neurons, whereas the inner portion of the cerebrum is composed of white matter and is composed of the axons of neuron. White matter is responsible for perception, relay of the sensory input via the thalamic pathway, and many other neurological functions, including complex thinking. The RAS, on the other hand, is a more primitive structure in the brainstem which includes the reticular formation (RF). The RAS has two tracts, the ascending and descending tract. The ascending tract, or ascending reticular activating system (ARAS), is made up of a system of acetylcholine-producing neurons, and works to arouse and wake up the brain. Arousal of the brain begins from the RF, through the thalamus, and then finally to the cerebral cortex. Any impairment in ARAS functioning, a neuronal dysfunction, along the arousal pathway stated directly above, prevents the body from being aware of its surroundings. Without the arousal and consciousness centers, the body cannot awaken, remaining in a comatose state.The severity and mode of onset of coma depends on the underlying cause. There are two main subdivisions of a coma: structural and diffuse neuronal. A structural cause, for example, is brought upon by a mechanical force that brings about cellular damage, such as physical pressure or a blockage in neural transmission. While a diffuse cause is limited to aberrations of cellular function, that fall under a metabolic or toxic subgroup.
Causes
The slowing of the bodys basal metabolic rate associated with hypothyroidism
Pernicious anemia where there is antibody production against parietal cells which normally produce gastric acid. The use of antacids or drugs that decrease gastric acid production (such as H2-receptor antagonists) or transport (such as proton pump inhibitors). A symptom of rare diseases such as mucolipidosis (type IV). A symptom of Helicobacter pylori infection which neutralizes and decreases secretion of gastric acid to aid its survival in the stomach. A symptom of atrophic gastritis or of stomach cancer. Radiation therapy involving the stomach. Gastric bypass procedures such as a duodenal switch and RNY, where the largest acid producing parts of the stomach are either removed, or blinded. VIPomas (vasoactive intestinal peptides) and somatostatinomas are both islet cell tumors of the pancreas. Pellagra, caused by niacin deficiency. Chloride, sodium, potassium, zinc and/or iodine deficiency, as these elements are needed to produce adequate levels of stomach acid (HCl). Sjögrens syndrome, an autoimmune disorder that destroys many of the bodys moisture-producing enzymes
Ménétriers disease, characterized by hyperplasia of mucous cells in the stomach also causing excess protein loss, leading to hypoalbuminemia. Presents with abdominal pain and edema

Risk Factors
Age
It was found that the incidence of achlorhydria in patients under the age of 60 was around 2.3%, whereas it was 5% in patients over the age of 60. In a persons 30s, the prevalence is about 2.5%, and increases to 12% in a persons 80s. An absence of hydrochloric acid increases with advancing age.