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Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs.Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck, including the special senses of vision, taste, smell, and hearing.
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).
Contralateral brain. The contralateral organization of the forebrain (Latin: contra‚ against; latus‚ side; lateral‚ sided) is the property that the hemispheres of the cerebrum and the thalamus represent mainly the contralateral side of the body. Consequently, the left side of the forebrain mostly represents the right side of the body, and ...
Cranial nerves; CN 0 – Terminal; CN I – Olfactory; CN II – Optic; CN III – Oculomotor; CN IV – Trochlear; CN V – Trigeminal; CN VI – Abducens; CN VII – Facial; CN VIII – Vestibulocochlear; CN IX – Glossopharyngeal; CN X – Vagus; CN XI – Accessory; CN XII – Hypoglossal
The optic chiasm is the primary cause of decussation; nasal fibers of the optic nerve cross (so each cerebral hemisphere receives contralateral—opposite—vision) to keep the interneuronal connections responsible for processing information short. All sensory and motor pathways converge and diverge to the contralateral hemisphere. [5]
Alternating hemiplegia (also known as crossed hemiplegia) is a form of hemiplegia that has an ipsilateral cranial nerve palsies and contralateral hemiplegia or hemiparesis of extremities of the body. The disorder is characterized by recurrent episodes of paralysis on one side of the body. [ 1 ]
Central facial paralysis/palsy often has similar characteristics with stroke patients. Because of uncrossed areas from the ipsilateral and the supranuclear areas, movements in the frontalis and upper orbicularis oculi are often spared. [3] Facial movement can be present on the affected side when the person expresses emotion.
The latter relay signals from the abducens nucleus to the contralateral oculomotor nucleus, where motoneurons drive the contraction of the ipsilateral medial rectus muscle (hence, contralateral to the abducens nucleus that issues the command); contraction of this muscle rotates the eye inward (adduction).