Fotorreceptores de la retina: Conos y Bastones -Centro de Oftalmología Bonafonte. Barcelona (España)
Retinal Photoreceptors: Cones and Rods
Overview of Retinal Photoreceptors
- The retinal photoreceptors, known as cones and rods, were first described in 1866. They are highly specialized neurons that are sensitive to light.
- Both types of photoreceptors share a similar basic structure but differ in complexity and function.
Structure of Photoreceptors
- Photoreceptors have an elongated shape with a cell body containing the nucleus, which is larger in cones than in rods.
- The external segment contains visual pigments crucial for light sensitivity; rods have independent discs while cones have membrane folds.
Visual Pigments
- Rods contain rhodopsin (opsin + retinal), essential for vision in low light, while cones contain photopsins sensitive to different wavelengths (blue, green, red).
Signal Transduction Process
- Light activation of visual pigments initiates a process called phototransduction, converting light into nerve impulses.
Internal Segments and Functions
- The internal segment has two key parts: the ellipsoid (rich in mitochondria for energy supply) and the myoid (contains Golgi apparatus and ribosomes for protein synthesis).
- The connecting segment serves as a cytoplasmic bridge between external and internal segments, facilitating biosynthesis transport.
Connector Fibers and Synaptic Terminals
- The external connector fiber is more developed in rods than cones; it contains neurotubules and neurofilaments.