Coma
Channel: 宇宙のすべての知識 プリンシピア
Date: 2019-02-01

Coma, by Wikipedia https://en.wikipedia.org/wiki?curid=5721 / CC BY SA 3.0

#Intensive_care_medicine
#Emergency_medicine
#Symptoms_and_signs:_Cognition,_perception,_emotional_state_and_behaviour
#Coma
Coma

Coma is a state of unconsciousness in which a person cannot be awakened; fails to respond normally to painful stimuli, light, or sound; lacks a normal wake-sleep cycle; and does not initiate voluntary actions. A person in a state of coma is described as being "comatose". A comatose state may derive from natural causes, or may be medically induced.

A comatose person exhibits a complete absence of wakefulness and is unable to consciously feel, speak, hear, or move. Clinically, a coma can be defined as the inability to consistently follow a one-step command.  It can also be defined as a score of ≤ 8 on the Glasgow Coma Scale lasting ≥ 6 hours. For a patient to maintain consciousness, two important neurological components must function. The first is the cerebral cortex—the gray matter that forms the outer layer of the brain. The other is a structure located in the brainstem, called reticular activating system (RAS).

Injury to either or both of these components is sufficient to cause a patient to experience a coma. The cerebral cortex is a group of tight, dense, "gray matter" composed of the nuclei of the neurons whose axons then form the "white matter," and is responsible for perception, relay of the sensory input via the thalamic pathway, and many other neurological functions, including complex thinking.

RAS, on the other hand, is a more primitive structure in the brainstem which includes the reticular formation (RF). The RAS area of the brain has two tracts, the ascending and descending tract. Made up of a system of acetylcholine-producing neurons, the ascending track, or ascending reticular activating system (ARAS), works to arouse and wake up the brain, from the RF, through the thalamus, and then finally to the cerebral cortex. A failure in ARAS functioning ma...