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Rod
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A rod is one of the two types of photoreceptor in the retina, the cells that turn light into a signal. The other is the cone, and what separates them is the shape of the outer segment, which is the outer part of the cell.
In a rod that outer segment is elongated, as the name suggests, and inside it carries a stack of membrane discs, one on top of another. Those discs are loaded with rhodopsin, its light-sensitive pigment, the molecule that reacts to light.
Rhodopsin is far more sensitive than the cone opsins, the equivalent pigments in the other cell. That is why, in a dark room, there is not enough light to activate the cones and vision depends on rods alone. Rods are the eye's night camera: they work with very little light.
In brief
A rod is one of the retina's two types of photoreceptor, and it differs from a cone in the shape of its outer segment.
That elongated outer segment holds a stack of membrane discs loaded with rhodopsin, its light-sensitive pigment.
Rhodopsin is far more sensitive than the cone opsins, so in a dark room vision depends on rods alone.
Rods are the eye's night camera: they work with very little light.
Sources (1)
- OpenStax, Rice UniversityAnatomy and Physiology 2e, 14.1 Sensory PerceptionPublished
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