CN 2: Optic Nerve (SIMPLE scheme + Animation)
Content:
0:00 Introduction
01:02 Optic Nerve Scheme
03:18 Eye Anatomy
04:47 Retina
07:48 Visual Field
09:47 Course of the Visual Pathway
16:33 Visual Pathway Collaterals
18:36 Clinical Relevance
21:21 Recap
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Visual Pathway Scheme / Overview:
- Visual Stimuli - 1st 2nd and 3rd order neurons in retina - Optic Nerve - Half fibers cross the optic chiasma - Optic Tract - Lateral Geniculate Body - Primary Visual Cortex
Eye Anatomy:
- Cornea
- Anterior Chamber
- Pupil
- Iris
- Lens
- Posterior Chamber
- Ciliary Muscles
- Sclera
- Choroid
- Retina
- Optic Disc
- Vitreous Humor
- Hyaloid Canal
Retina:
- 1st order neurons: Rods and Cones
- 2nd order neurons: Bipolar cells
- 3rd order neurons: Ganglion cells
Olfactory Neuron:
- Dendrites detect smell through a g-protein couples membrane receptor.
- Signals pass through the cell body and axon
- Axons form nerve bundles (fila olfactoria)
Visual Fields:
- Fovea: Highest acuity of vision
- Retina is split into temporal half and the retinal half
- Medial fibers go to contralateral side
- Lateral fibers go to ipsilateral side
Course of the Visual Pathway:
- 1st neuron: Rods and Cones
- 2nd neurons: Bipolar cells
- 3rd neurons: Ganglion cells
- Optic Nerve (nervus opticus)
- Optic Chiasma (chiasma opticum)
- Optic Tract (tractus opticus)
- 4th order neuron lateral geniculate bodies
- Optic Radiations (radiato optica) and Meyer's Loop
- Primary Visual Cortex (area 17)
Visual Pathway Collaterals:
- Accomodation reflecx
- Direct and consensual light reflex
- Saccadic eye movement
- Tectospinal tract (for reflectory movements according to unexpected visual irritation)
- Medial Longitudinal fasciculus
Clinical Relevance:
- Lesion in optic nerve: complete blindness of affected side
- Lesion in optic chiasma: Visual field Bitemporal hemianopia
- Lesion in optic tract and geniculate body: Homonymous hemianopia
- Lesion in Optic Radiation: Quadrantanopia
- Lesion in the visual cortex causes cortical blindness: Homonymous hemianopias with or without macular involvement
Sources:
- Singh, I. (2017). Human neuroanatomy (10th ed.). Helwany M, Bordoni B. Neuroanatomy, Cranial Nerve 1 (Olfactory) [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-
- Kozlowski, T. (2017). Memorix Anatomy: The Complete Study Guide. 2nd ed. Thieme Medical Publishers.