The trochlear nucleus () is the motor nucleus of the

trochlear 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 pu ...

( cranial nerve IV). It is located in the medial

midbrain The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum. It is functionally associated with vision, hearing, mo ...

Structure

The trochlear nucleus is located in the

, at an intercollicular level between the

superior colliculus In neuroanatomy, the superior colliculus () is a structure lying on the tectum, roof of the mammalian midbrain. In non-mammalian vertebrates, the Homology (biology), homologous structure is known as the optic tectum or optic lobe. The adjective f ...

and

inferior colliculus The inferior colliculus (IC) (Latin for ''lower hill'') is the principal midbrain nucleus of the Auditory system, auditory pathway and receives input from several peripheral brainstem nuclei in the auditory pathway, as well as inputs from the aud ...

. As with all motor nuclei of cranial nerves, it is located near the midline (i.e. in the medial midbrain). It is embedded within the

medial longitudinal fasciculus The medial longitudinal fasciculus (MLF) is a prominent bundle of nerve fibres which pass within the ventral/anterior portion of periaqueductal gray of the mesencephalon (midbrain). It contains the interstitial nucleus of Cajal, responsible ...

. It is situated immediately below the nucleus of the oculomotor nerve (CN III) (the only other cranial nerve with a nucleus in the

besides the

mesencephalic nucleus of trigeminal nerve The mesencephalic nucleus of trigeminal nerve is one of the sensory nuclei of the Trigeminal nerve, trigeminal nerve (cranial nerve V). It is located in the brainstem. It receives Proprioception, proprioceptive sensory information from the muscles ...

, which functions in preserving dentition). The trochlear nucleus is unique in that its axons run dorsally and cross the midline at the trochlear decussation (located in the superior medullary velum) in the midbrain before emerging from the brainstem posteriorly/dorsally. In other words, trochlear nucleus on one side gives rise to the trochlear nerve on the contralateral side. A lesion of the trochlear nucleus thus affects the contralateral eye, whereas lesions of all other cranial nuclei affect the ipsilateral side.

Blood supply

The midbrain receives its arterial blood supply from the

posterior cerebral artery The posterior cerebral artery (PCA) is one of a pair of cerebral arteries that supply oxygenated blood to the occipital lobe, as well as the medial and inferior aspects of the temporal lobe of the human brain. The two arteries originate from the d ...

superior cerebellar artery The superior cerebellar artery (SCA) is an artery of the head. It arises near the end of the basilar artery. It is a branch of the basilar artery. It supplies parts of the cerebellum, the midbrain, and other nearby structures. It is the cause of t ...

, and

basilar artery The basilar artery (U.K.: ; U.S.: ) is one of the arteries that supplies the brain with oxygen-rich blood. The two vertebral arteries and the basilar artery are known as the vertebral basilar system, which supplies blood to the posterior part o ...

; disruption of blood flow through any of these vessels may disrupt blood supply to the trochlear nucleus.

Additional images

File:Gray697.png, Nuclei of origin of cranial motor nerves schematically represented; lateral view. File:Gray774.png, Scheme showing central connections of the optic nerves and optic tracts. File:Brain stem sagittal section.svg, Brain stem sagittal section

References

External links

* - "Brainstem, Cranial Nerve Nuclei, Sagittal Section, Medial View" Midbrain {{Neuroanatomy-stub