Notes on Visual Pathways

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Mechanism of Vision:

• Photopigments in rods and cones absorb photons.

• Molecular structure of these pigments altered.

• Na channels close.

• Hyperpolarization.

• Less neurotransmitter released.

• Rods and cones release less neurotransmitter in light, and more neurotransmitter in dark.

• Rods and cones are connected to bipolar cells that are connected to ganglion cells.

Accommodation Reflex:

• Ciliary muscle contracted.

• Pupillae muscle contracted.

• Convergence.

Lesions in Visual Pathways:

• Optic nerve: blindness and loss of sensory light reflex.

• Optic chiasm compression due to pituitary tumor or meningioma: loss of peripheral vision in both temporal fields, also known as bitemporal heteronymous hemianopia.

Visual Pathway Lesions:

Visual Pathway Lesions

Pupillary Light Reflex:

• Light shone into one eye; impulses carried by optic nerve through to Edinger-Westphal nucleus, then distributed to both eyes.

• Edinger-Westphal nucleus = parasympathetic nucleus of oculomotor nerve.

Accommodation-Convergence Reaction:

• Occurs when the eye focuses on a nearby object after looking at a distant object.

• Involves: ciliary ganglion, preganglionic parasympathetic fibers, Edinger-Westphal nucleus, post-ganglionic parasympathetic fibers, ciliary muscle.

Additional Readings:

Basic Neurology

1. Peripheral Nervous System
2. Central Nervous System
3. The Ventricular System
4. The Spinal Cord
5. The Brain Stem
6. The Cerebellum
7. Visual Pathways
8. Diencephalon
9. Basal Ganglia
10. Cerebral Cortex
11. Sleep Disorders
12. Autonomic Nervous System
13. Cranial Nerves and Parasympathetic Ganglia
14. Cells of the Nervous System
15. Cerebrospinal fluid
16. Additional short notes on Cerebrum
17. Functions and Diseases of Cerebrum
18. Subcortical Grey Matter
19. Notes on The Spinal Cord
20. Regulation of Heart Rate by Autonomic Nervous System
21. Action Potentials, Axon Conduction, and Neuromuscular Junction
22. Types of Seizures
23. What is a Cough Reflex?
24. Notes on Congenital Prosopagnosia
25. Findings in Parkinson's Disease
26. Types of Heat Strokes
27. Types of Strokes
28. What is Benign Intracranial Hypertension?
29. What is Cauda Equina Syndrome?
30. Cranial Nerve Locations in Brain Stem

Neurology Videos

1. Video of Neurology Examination in a Clinical Setting

Medical Images

Useful Medical Images & Diagrams (link opens in a new window)

Related Topics

1. Nervous System Disorders
2. Histology of Nervous Tissue
3. Cranial Nerve Reflexes
4. Motor System Examination

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