Injury to either or both of the cerebral cortex or the reticular activating system (RAS) is sufficient to cause a person to enter coma. The cerebral cortex is the outer layer of neural tissue of the cerebrum of the brain. 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 track, 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. Toxin-induced comas are caused by extrinsic substances, whereas metabolic-induced comas are caused by intrinsic processes, such as body thermoregulation or ionic imbalances(e.g. sodium). For instance, severe hypoglycemia (low blood sugar) or hypercapnia (increased carbon dioxide levels in the blood) are examples of a metabolic diffuse neuronal dysfunction. Hypoglycemia or hypercapnia initially cause mild agitation and confusion, but progress to obtundation, stupor, and finally, complete unconsciousness. In contrast, coma resulting from a severe traumatic brain injury or subarachnoid hemorrhage can be instantaneous. The mode of onset may therefore be indicative of the underlying cause. Structural and diffuse causes of coma are not isolated from one another, as one can lead to the other in some situations. For instance, coma induced by a diffuse metabolic process, such as hypoglycemia, can result in a structural coma if it is not resolved. Another example is if cerebral edema, a diffuse dysfunction, leads to ischemia of the brainstem, a structural issue, due to the blockage of the circulation in the brain.
symptom of Rabies
symptom of Japanese encephalitis
symptoms of Rabies
symptom of West Nile fever
symptom of Eastern equine encephalitis
symptom of Scabies
symptom of Chikungunya
symptom of Trench fever