Pain - itami (English spelling)

Japanese: 痛み - いたみ（英語表記）pain

The term is used in two senses: pain as a sensation and pain as an emotion. Pain as a sensation is caused by stimulation of pain receptors distributed in various parts of the body, such as pain points on the skin, muscles, joints, and internal organs. Pain receptors are not specialized cells, but free nerve endings. There is no specific stimulus that causes pain, and any strong stimulus will cause pain regardless of the type. This is called a noxious stimulus. Other stimuli include pain-inducing substances such as histamine and serotonin. Pain is physiologically divided into somatic pain and visceral pain, but since visceral pain fibers are distributed in large numbers in blood vessels and serous membranes and few in the organs themselves, pain is not felt when the organ is cut, but is often felt when pain-inducing substances are produced due to an abnormality in the organ. Somatic pain is divided into a stabbing pain and a continuous dull pain. The former is transmitted to the brain by Aδ fibers, and the latter by thinner C fibers. Morphine acts on the dull pain pathway in the brainstem and suppresses it. Itch can also be considered a form of pain sensation.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

感覚としての痛覚と感情としての苦痛の二様の意味で用いられる。感覚としての痛覚は皮膚の痛点や筋肉，関節，内臓など身体各部に分布する痛覚受容器に対する刺激によって生じる。痛覚受容器は特殊な細胞ではなく，神経の自由終末である。痛みを引起す刺激は特定のものではなく，強い刺激なら種類を問わず痛みを感じる。これを侵害刺激という。そのほかヒスタミンやセロトニンのような発痛物質が刺激になる。痛みは生理学的に体性痛と内臓痛に分けられるが，内臓の痛覚線維は血管や漿膜に多く分布し，器官自体には少いので，器官を切っても痛みを感じず，その器官の異常で発痛物質を生じたとき感じることが多い。体性の痛覚はちくちくする刺す痛みと持続的な鈍い痛みに区別される。前者はAδ線維により，後者はそれより細いC線維によって脳に伝えられる。モルヒネは脳幹で鈍い痛みの経路に作用して，これを抑制する。かゆみも痛覚の一変型と考えられる。

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