Trochlear nerve
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The trochlear nerve is the fourth cranial nerve and is the motor nerve of the superior oblique muscle of the eye.
Gross anatomy
Nucleus and cisternal portion
It is the only cranial nerve to exit the brainstem posteriorly, immediately below the inferior colliculus. It then rounds the cerebral peduncles in the ambient cistern coursing, along with the oculomotor nerve, between the superior cerebellar artery and posterior cerebral artery, and pierces the dura in-between the free and attached edge of tentorium cerebelli.
Cavernous sinus portion
Within the cavernous sinus the trochlear nerve is located initially below the oculomotor nerve in the lateral wall of the sinus, although by the time it reaches the superior orbital fissure it is above it (outside the tendinous ring). It is the "Tarts" in the infamous mnemonic.
Orbital portion
Having entered the orbit lateral and superior to the tendinous ring it arches up and medially (see Figure 3) above superior rectus and levatore palpebrae superioris superioris to innervate the superior oblique.
-<p>The<strong> trochlear nerve</strong> is the fourth <a href="/articles/cranial-nerves">cranial nerve</a> and is the motor nerve of the <a title="Superior oblique muscle" href="/articles/superior-oblique-muscle">superior oblique muscle of the eye</a>.</p><h4>Gross anatomy</h4><h5>Nucleus and cisternal portion</h5><p>It is the only cranial nerve to exit the <a href="/articles/brainstem">brainstem</a> posteriorly, immediately below the <a href="/articles/inferior-colliculus">inferior colliculus</a>. It then rounds the <a href="/articles/cerebral-peduncles">cerebral peduncles</a> in the <a href="/articles/ambient-cistern">ambient cistern</a> coursing, along with the <a href="/articles/oculomotor-nerve">oculomotor nerve</a>, between the <a href="/articles/superior-cerebellar-artery">superior cerebellar artery</a> and <a href="/articles/posterior-cerebellar-artery">posterior cerebral artery</a>, and pierces the dura in-between the free and attached edge of <a href="/articles/tentorium-cerebelli">tentorium cerebelli</a>.</p><h5>Cavernous sinus portion</h5><p>Within the <a href="/articles/cavernous-sinus">cavernous sinus</a> the trochlear nerve is located initially below the <a href="/articles/oculomotor-nerve">oculomotor nerve</a> in the lateral wall of the sinus, although by the time it reaches the <a href="/articles/superior-orbital-fissure">superior orbital fissure</a> it is above it (outside the <a href="/articles/tendinous-ring">tendinous ring</a>). It is the "Tarts" in the infamous <a href="/articles/superior-orbital-fissure-nerves-mnemonic">mnemonic</a>.</p><h5>Orbital portion</h5><p>Having entered the <a href="/articles/orbit">orbit</a> lateral and superior to the <a href="/articles/tendinous-ring">tendinous ring</a> it arches up and medially (see Figure 3) above <a href="/articles/superior-rectus">superior rectus</a> and <a href="/articles/levatore-palpebra-superioris">levatore palpebrae superioris</a> to innervate the <a href="/articles/superior-oblique">superior oblique</a>.</p>- +<p>The<strong> trochlear nerve</strong> is the fourth <a href="/articles/cranial-nerves">cranial nerve</a> and is the motor nerve of the <a href="/articles/superior-oblique-muscle">superior oblique muscle of the eye</a>.</p><h4>Gross anatomy</h4><h5>Nucleus and cisternal portion</h5><p>It is the only cranial nerve to exit the <a href="/articles/brainstem">brainstem</a> posteriorly, immediately below the <a href="/articles/inferior-colliculus">inferior colliculus</a>. It then rounds the <a href="/articles/cerebral-peduncles">cerebral peduncles</a> in the <a href="/articles/ambient-cistern">ambient cistern</a> coursing, along with the <a href="/articles/oculomotor-nerve">oculomotor nerve</a>, between the <a href="/articles/superior-cerebellar-artery">superior cerebellar artery</a> and <a title="Posterior cerebral artery" href="/articles/posterior-cerebral-artery">posterior cerebral artery</a>, and pierces the dura in-between the free and attached edge of <a href="/articles/tentorium-cerebelli">tentorium cerebelli</a>.</p><h5>Cavernous sinus portion</h5><p>Within the <a href="/articles/cavernous-sinus">cavernous sinus</a> the trochlear nerve is located initially below the <a href="/articles/oculomotor-nerve">oculomotor nerve</a> in the lateral wall of the sinus, although by the time it reaches the <a href="/articles/superior-orbital-fissure">superior orbital fissure</a> it is above it (outside the <a href="/articles/tendinous-ring">tendinous ring</a>). It is the "Tarts" in the infamous <a href="/articles/superior-orbital-fissure-nerves-mnemonic">mnemonic</a>.</p><h5>Orbital portion</h5><p>Having entered the <a href="/articles/orbit">orbit</a> lateral and superior to the <a href="/articles/tendinous-ring">tendinous ring</a> it arches up and medially (see Figure 3) above <a href="/articles/superior-rectus">superior rectus</a> and <a href="/articles/levatore-palpebra-superioris">levatore palpebrae superioris</a> to innervate the <a href="/articles/superior-oblique">superior oblique</a>.</p>