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101 Figure 27: Vascular Supply of the Optic Nerve Head, Choroid and RetinaThe ophthalmic artery is a branch of the internal carotid artery, which in turn, supplies the posterior ciliary (to choroid and outer retina) and central retinal (to inner retina) arteries. The central retinal artery (CRA) enters the optic nerve about 1 cm posterior to the globe, and an embolus may ...
102 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...
103 Figure 43: How the Brain Makes Sense of What It Sees - The Dorsal and Ventral Visual Pathways, and a 3 Tiered Approach to Vision1) Ventral ("what") stream - this begins with the ‘P' retinal ganglion cells à parvocellular layers of the lateral geniculate nucleus (LGN, 3-6) à V1/striate cortex (in blue) à V4/V4a (fusiform and lingual gyri) à occipitotemporal regions. 2) Dorsal ("where") stream - this begins with the ‘M...
104 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...
105 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...
106 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...
107 Figure 51: Lateral Medullary Lesion Causing Saccadic Dysmetria (Supplement)
108 Figure 51: Lateral Medullary Lesion Causing Saccadic Dysmetria (Supplement)
109 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...
110 Figure 53: Vascular Distribution and Anatomy Relevant to the Lateral Medullary (Wallenberg) Syndrome (Supplement)
111 Figure 53: Vascular Distribution and Anatomy Relevant to the Lateral Medullary (Wallenberg) Syndrome (Supplement)
112 Figure 61: Vascular Distribution and Anatomy (Including 6th, 7th, 8th Nerves, MLF) of the PonsIn this axial section of the pons, the proximity of the 7th (VII) and 8th (VIII) fascicles can be appreciated, and a lateral inferior pontine syndrome (anterior inferior cerebellar artery, AICA territory), which could involve both of these fascicles, could cause acute prolonged vertigo accompanied b...
113 Figure 61: Vascular Distribution and Anatomy (Including 6th, 7th, 8th Nerves, MLF) of the Pons (Supplement)
114 Figure 61: Vascular Distribution and Anatomy (Including 6th, 7th, 8th Nerves, MLF) of the Pons (Supplement)
115 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...
116 Figure 64: The Course of the 3rd (III) Nerve (Supplement)
117 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...
118 Figure 65: Vascular Distribution and Anatomy (Including 3rd Nerve) of the Rostral Midbrain (Supplement)
119 Figure 65: Vascular Distribution and Anatomy (Including 3rd Nerve) of the Rostral Midbrain (Supplement)
120 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 ...
121 Figure 68: The Course of the 4th (IV) Nerve (Supplement)
122 Figure 69: Vascular Distribution and Anatomy (Including 4th Nerve) of the Caudal MidbrainIn this axial section of the midbrain at the level of the inferior colliculus, the 4th nuclei are located ventral to the periaqueductal grey, dorsal to the medial longitudinal fasciculus (MLF) and medial to the oculosympathetic tract. Fascicles exit the nucleus dorsally and decussate at the anterior...
123 Figure 69: Vascular Distribution and Anatomy (Including 4th Nerve) of the Caudal Midbrain (Supplement)
124 Figure 69: Vascular Distribution and Anatomy (Including 4th Nerve) of the Caudal Midbrain (Supplement)
125 Figure 80: Vascular Distribution and Anatomy Relevant to the Medial Medullary SyndromeThis axial section of the medulla highlights those structures that, when damaged, are often responsible for spontaneous upbeat nystagmus (UBN). The nucleus of Roller and nucleus intercalatus normally have an inhibitory influence over the cerebellar flocculus, and when there is a lesion of Roller/int...
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