Νευρόσπαστον literally means "the thing pulled by strings" (from νεῦρα — "sinews," "tendons," "strings"). In antiquity it is the wooden marionette twitched by puppeteers on invisible strings. A standard image of the philosophical tradition: the person driven by the passions is a νευρόσπαστον — a puppet whose "strings" are his own false judgments. Plato already uses the image at Laws 644d–645a, but evaluatively (god pulls the "golden string" of reason). Marcus preserves the image but inverts the emphasis: the ruling part must not allow itself to be twitched.

Med. 2.2: μηκέτι καθ' ὁρμὴν ἀκοινώνητον νευροσπαστηθῆναι — "let it [the ruling part] no longer be twitched, like a puppet on strings, by an unsocial impulse." Cf. Med. 6.16, 6.28, 7.3, 7.29, 12.19 — the image recurs; Med. 3.16: "the person led by passion is a νευρόσπαστον." The Greek background: Plat. Leg. 644d–645a; Plut. De E 384e.

In 02-02 the image works as the anti-norm for the TERMruling part. The logic: if a person is a material weaving of "sinews, veinlets, arteries" (see flesh-as-network), then his inner life too may come to be governed by the same material — he may become a marionette of his own tissues. The Stoic discipline consists in reversing this: it is not the flesh that pulls the mind by its strings, but the mind that remains master over impulses (TERMhorme). The paired image is flesh-as-network: marionette and puppeteer are cut from the same material — the whole question is who is leading whom.