Vision and Sensory Processing

Retina Structure and Function

  • Retinal Components: Ganglia, bipolar neurons, and blood vessels are in front of the retina, causing obstruction.
  • Peripheral Vision: Less clear due to obstruction from internal structures.
  • Fovea: Central region of the retina with no obstructions, enabling clear vision.

Photoreceptor Cells

  • Types: Rods (high sensitivity, low light) and cones (color vision, require bright light).
  • Rod Structure: Contains rhodopsin; sensitive to dim light.
  • Cone Structure: Has different opsins for color detection.

Light Processing

  • Transduction: Photoreceptors convert light into nervous signals.
  • Retinal and Opsin Interaction: Photon activation changes retinal conformation from cis to trans, causing signal transmission.
  • Bleaching: Exposure to bright light overwhelms rods, causing temporary vision loss.

Vision and Color Perception

  • Color Detection: Cones enable color differentiation based on wavelengths absorbed.
  • Color Blindness: Commonly red-green color blindness due to opsin deficiencies.
  • Animal Vision: Different species perceive color based on available opsins; some detect UV light.

Somatosensation

  • Definition: Includes touch, temperature, pain, proprioception, and kinesthesia.
  • Receptors: Free nerve endings for pain and temperature; specialized receptors for touch.
  • Thermoreceptors and Nociceptors: Respond to extreme temperatures and pain; behaviors initiated to avoid harm.

Sensory Pathways

  • Afferent vs Efferent Neurons: Afferent carries sensory input to the brain, efferent transmits motor signals.
  • Contralateral and Ipsilateral Transmission: Sensory signals often cross sides (contralateral), while some cranial nerves process on the same side (ipsilateral).

Ascending Pathways

  • Dorsal Column System: Carries touch and proprioception information; decussates in the medulla.
  • Spinothalamic Tract: Carries pain and temperature signals; decussates immediately in the spinal cord.
  • Trigeminal System: Manages sensations from the face, connected to cranial nerves.

Central Processing of Sensory Information

  • Decussation: Crossing of neural pathways crucial for sensory processing; involves thalamus for most senses (except olfaction).
  • Processing Locations: Specific brain regions (e.g., brainstem) process signals before reaching the cortex; sound localization is an example.
  • Optic Chiasma: Visual signals decussate; important for coordinating vision across both hemispheres.