Vision

  • Visual System Overview

    • Includes visual pathways, reflexes, and processing.

  • Visual Pathway

    • Visual field divided into quadrants: upper, lower, right, left (nasal and temporal).

    • Retina receives visual field projection; image is inverted and crossed.

  • Retina Functionality

    • Temporal half of visual field projects to nasal half of retina.

    • Nasal half projects to temporal half; upper and lower field relationships similarly defined.

  • Optic Chiasma

    • Fibers partially cross: left visual fields to right optic tract and vice versa.

    • Optic tracts synapse in lateral geniculate nucleus (LGN), leading to optic radiation.

  • Optic Radiation

    • Fiber divisions: upper field (Loop of Meyer, temporal lobe) and lower field (parietal lobe).

    • Termination in Lingual gyrus (upper) and Cuneus (lower).

  • Visual Reflexes

    • Light reflex: involves retina, optic nerve, and oculomotor pathways leading to pupil constriction.

    • Accommodation reflex: involves lens thickening, convergence, and pupil constriction coordinated by optic and frontal eye fields.

  • Saccadic Movements

    • Quick eye movements toward stimuli, controlled by superior colliculus and frontal eye field for visual attention and discrimination.

  • Eye Anatomy

    • Sclera, conjunctiva, cornea, iris, pupil, macula, fovea, and optic disc defined.

    • Macula responsible for central vision; fovea has highest visual acuity.

  • Retinal Anatomy

    • Composed of three neuron layers: photoreceptors, bipolar cells, ganglion cells.

    • Horizontal and amacrine cells assist with lateral communication and signal processing.

  • Phototransduction Process

    • Light absorbed triggers a cascade that hyperpolarizes photoreceptors, decreasing neurotransmitter glutamate release.

    • Rods and cones differ in sensitivity and function: rods for night vision, cones for color and detail.

  • Ganglion Cells & Responses

    • Respond to light changes with action potentials; crucial for detecting differences in illumination.

    • Different types: M cells for motion, P cells for color and fine detail.

  • Primary Visual Cortex

    • Six layers receiving M and P type signals, organized for processing color, motion, and shape.

    • Dorsal pathway (motion/depth) and ventral pathway (color/form) for further processing in the brain.