Anatomy and Pathways of the Visual System

Introduction

• Overview of anatomical structures in the visual system.
• Pathways for transmitting visual information to the CNS.
• Sensory receptors specialize in detecting specific energy types.

Light and Photoreceptors

• Photoreceptors in the Retina: Respond to light energy.
• Three Dimensions of Light:
  • Hue (Color): Determined by wavelength.
  • Brightness: Determined by amplitude of light waves.
  • Saturation: Purity of light (lack of color mixing).

Visual Spectrum

• Human eye detects wavelengths between 400-750 nanometers.
• Shorter wavelengths = bluish light; longer wavelengths = reddish light.
• Brightness is related to wave amplitude.

Anatomy of the Eye

• Retina:
  • Multi-layered, light-sensitive surface at the back of the eye.
  • Converts electromagnetic energy to neural impulses.
  • Contains approximately 126 million photoreceptor cells (rods and cones).
  • Rods: Respond to dim light, detect brightness, more numerous than cones, located peripherally.
  • Cones: Detect color and detail, function in bright light, concentrated in the center (fovea).

Retinal Structure

• Layers in Retina:
  • Photoreceptor cells.
  • Bipolar and ganglion cells: Transmit information to the brain.
  • Ganglion cell axons form the optic nerve.
  • Blind Spot: Area with no photoreceptors where optic nerve exits.

Visual Processing

• Fovea: High concentration of cones, essential for detailed vision.
• Peripheral Vision: Light falls outside the fovea, less detail.

Pathways to the Brain

• Optic Nerve: Transmits visual information to the brain.
• Optic Chiasm: Axons cross sides, contralateral processing.
• Visual Cortex Processing:
  • Image is upside down on retina.
  • Thalamus Role: Relay station for sensory information.

Visual Pathways

• Geniculostriate System: Via lateral geniculate nucleus to primary visual cortex (V1).
• Tectopulvinar System: Through superior colliculus to pulvinar nucleus, then visual cortex.

Primary and Secondary Visual Processing

• V1 (Primary Visual Cortex): Initial processing (lines, edges).
• V2 (Secondary Area): Further processing (angles, textures).
• Subsequent areas (V3, V4, V5/MT) handle complex processing (color, movement).

Visual Pathways in Cortex

• Dorsal Pathway (How/Where): Guides movements, from occipital to parietal lobe.
• Ventral Pathway (What): Identifies objects, from occipital to temporal lobe.

Conclusion

• Parallel processing allows for quick visual information transmission.
• Binding process integrates visual information for comprehensive perception.

End of lecture on visual system anatomy and pathways.