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26 Medullary Structures Relevant to the Ocular Motor and Vestibular Consequences of Lateral Medullary (Wallenberg) SyndromeThis is an axial section of the medulla showing the structures that, when damaged, are responsible for the vestibular and ocular motor features of the lateral medullary or Wallenberg syndrome. The nucleus prepositus hypoglossi (NPH) and medial vestibular nucleus (MVN) complex is important for horizo...Image
27 Saccadic Pathways in the Brainstem and Cerebellum & Mechanism for Saccadic Dysmetria in Wallenberg Syndrome - Abnormal Function of the Brainstem/Cerebellar Saccadic Pathways with a Left Wallenberg SyndromeThe end result of a lesion involving the climbing fibers within the left lateral medulla is deficient rightward saccades (contralesional hypometric saccades), and over-active leftward saccades (ipsilesional hypermetric saccades), and ipsilesional ocular lateropulsion given this baseline imbalance. M...Image
28 The Utriculo-Ocular Motor Pathways - Physiologic and Pathologic Ocular Tilt Reaction: OTR Diagram Pathologic EOMs Labelled (Figure 3)A skew deviation is a non-paralytic vertical ocular misalignment that is due to imbalance in the utriculo-ocular motor pathways. While vestibular jerk nystagmus is a consequence of static semicircular canal pathway imbalance (e.g., left-beating nystagmus due to acute right vestibular hypofunction fr...Image
29 The Utriculo-Ocular Motor Pathways - Physiologic and Pathologic Ocular Tilt Reaction: Pathologic OTR (Figure 2)A skew deviation is a non-paralytic vertical ocular misalignment that is due to imbalance in the utriculo-ocular motor pathways. While vestibular jerk nystagmus is a consequence of static semicircular canal pathway imbalance (e.g., left-beating nystagmus due to acute right vestibular hypofunction fr...Image
30 Pons: 6th, 7th, 8th, and Middle Cerebellar Peduncle AnatomyFrom this cross-section of the pons, the proximity of the 7th and 8th fascicles can be appreciated, and a lateral inferior pontine syndrome (anterior inferior cerebellar artery territory), which could involve both of these fascicles, could cause acute prolonged vertigo accompanied by a + ipsilateral...Image
31 Central Anatomy of the Third NerveSeen here is an axial section of the midbrain at the level of the superior colliculus. The paired nuclei are located ventral to the periaqueductal grey, and the midline central caudal nucleus (CCN) is located between the right and left nuclei. The CCN sends projections to bilateral levator palpebrae...Image
32 Figure 17: Bony Structures Relevant to the OrbitThe frontal, sphenoid, maxillary, ethmoid, and lacrimal bones make up the orbit. Structures passing through the optic canal include the optic nerve, oculosympathetic tract and ophthalmic artery. Structures passing through the superior orbital fissure include the superior ophthalmic vein, cranial ner...Image
33 Figure 1: Oculosympathetic Pathway for Pupillary DilationThe oculosympathetic tract is an uncrossed pathway that begins in the hypothalamus, with fibers descending in the brainstem (1st order, commonly affected in a lateral medullary syndrome), synapsing in the lower cervical/upper thoracic spinal cord (interomediolateral cell columns of C8-T2, also refer...Image
34 Figure 24: Typical Visual Field Defects Associated with Discrete Lesions Along the Visual PathwaysSpecific monocular or binocular visual field defects can be highly localizing when the neuroanatomy of the visual pathways is understood. The temporal visual field corresponds to the nasal retina, while the nasal visual field corresponds to the temporal retina. 1) Left optic nerve lesion - while an ...Image
35 Figure 2: Parasympathetic Pathway for Pupillary ConstrictionA bright light is shone in one eye, light enters the pupil and hyperpolarizes retinal photoreceptors which activates retinal ganglion cells. These signals propagate along the optic nerves, chiasm, optic tracts, and fibers responsible for the light reflex then synapse in the dorsal midbrain (prior to...Image
36 Figure 46: The Course of the 6th (VI) NerveThe sixth nucleus is located dorsally, adjacent to the 4th ventricle, in the lower pons. The genu of the facial (7th) nerve wraps around the 6th nucleus, creating the facial colliculus, which bulges into the 4th ventricle. After the 6th nerve leaves the pons, it follows a vertical course along the c...Image
37 Figure 50: Anatomy and Physiology of the Saccadic PathwaysWhen a saccade is desired (or reflexively triggered), signals project from the saccade-related cortical eye fields to the superior colliculus, which serves to integrate and relay commands to the saccade generating brainstem circuitry. The inferior cerebellar peduncle (ICP) carries climbing fibers to...Image
38 Figure 51: Lateral Medullary Lesion Causing Saccadic DysmetriaA lesion of the left lateral medulla and inferior cerebellar peduncle (ICP) will cause decreased climbing fiber inhibition of the left dorsal vermis causing simple-spike (inhibitory) discharge of Purkinje cells to increase. Increased Purkinje cell firing leads to increased inhibition of the ipsilate...Image
39 Figure 51: Lateral Medullary Lesion Causing Saccadic Dysmetria (Supplement)Image
40 Figure 51: Lateral Medullary Lesion Causing Saccadic Dysmetria (Supplement)Image
41 Figure 53: Vascular Distribution and Anatomy Relevant to the Lateral Medullary (Wallenberg) SyndromeThis axial section of the medulla highlights those structures that, when damaged, are responsible for the vestibular and ocular motor features of the Wallenberg syndrome. The nucleus prepositus hypoglossi (NPH) and medial vestibular nucleus (MVN) complex is important for horizontal gaze-holding (neu...Image
42 Figure 53: Vascular Distribution and Anatomy Relevant to the Lateral Medullary (Wallenberg) Syndrome (Supplement)Image
43 Figure 53: Vascular Distribution and Anatomy Relevant to the Lateral Medullary (Wallenberg) Syndrome (Supplement)Image
44 Figure 64: The Course of the 3rd (III) NerveThe 3rd nucleus lies at the ventral border of the periaqueductal gray matter, at the level of the superior colliculus. In between the two nuclei is the midline central caudal nucleus (CCN), which innervates bilateral levator palpebrae muscles (explaining how a unilateral nuclear 3rd can cause bilate...Image
45 Figure 64: The Course of the 3rd (III) Nerve (Supplement)Image
46 Figure 65: Vascular Distribution and Anatomy (Including 3rd Nerve) of the Rostral MidbrainIn this axial section of the midbrain at the level of the superior colliculus, the paired 3rd nuclei are located ventral to the periaqueductal grey, and the midline central caudal nucleus (CCN) is located in between. The fascicles that exit the IIIrd nuclei carry the fibers destined to innervate the...Image
47 Figure 65: Vascular Distribution and Anatomy (Including 3rd Nerve) of the Rostral Midbrain (Supplement)Image
48 Figure 65: Vascular Distribution and Anatomy (Including 3rd Nerve) of the Rostral Midbrain (Supplement)Image
49 Figure 68: The Course of the 4th (IV) NerveThe 4th nucleus lies at the ventral border of the periaqueductal gray matter, at the level of the inferior colliculus. The fascicles exit the nucleus dorsally and decussate at the anterior medullary velum (anterior floor of the fourth ventricle), and then exit the brainstem dorsally. The peripheral ...Image
50 Figure 68: The Course of the 4th (IV) Nerve (Supplement)Image
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