Trochlear nerve
4th cranial nerve
The trochlear nerve (), (lit. pulley-like nerve) also known as the fourth cranial nerve, cranial nerve IV, or CN IV, is a cranial nerve that innervates a single muscle - the superior oblique muscle of the eye (which operates through the pulley-like trochlea). Unlike most other cranial nerves, the trochlear nerve is exclusively a motor nerve (somatic efferent nerve).
The trochlear nerve is unique among the cranial nerves in several respects:
It is the smallest nerve in terms of the number of axons it contains.
It has the greatest intracranial length.
It is the only cranial nerve that exits from the dorsal (rear) aspect of the brainstem.
It innervates a muscle, the superior oblique muscle, on the opposite side (contralateral) from its nucleus. The trochlear nerve decussates within the brainstem before emerging on the contralateral side of the brainstem (at the level of the inferior colliculus). An injury to the trochlear nucleus in the brainstem will result in an contralateral superior oblique muscle palsy, whereas an injury to the trochlear nerve (after it has emerged from the brainstem) results in an ipsilateral superior oblique muscle palsy.
The superior oblique muscle which the trochlear nerve innervates ends in a tendon that passes through a fibrous loop, the trochlea, located anteriorly on the medial aspect of the orbit.
“Trochlear nerve” enters the record as 4th cranial nerve. Crown Archives preserves that source wording while asking what Trochlear, nerve and cranial can confirm, complicate or overturn.
Why this record matters
“Trochlear nerve” is worth following because a concise public description often conceals a longer documentary argument. Here, Trochlear, nerve and cranial provides the most credible route into that argument.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Jan 15, 2026. The linked authority identifier is Q319584. None of the 0 selected statements returned an explicit reference.
A concise general-reference account can conceal disagreements about scope, terminology or the weight assigned to individual sources. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “Trochlear nerve”, its source revision and the description used here.
- Expand the search: follow Trochlear nerve primary sources, Trochlear nerve archive and Trochlear research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “Trochlear nerve”?
- What terminology or title could unlock a more precise catalogue search?
- Which institution is responsible for the underlying evidence?
Search terms from this dossier
This entry incorporates text from “Trochlear nerve” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.