BRAINCAKERods
Rods are photoreceptors that work in dim light. They contain the light-sensitive pigment rhodopsin, made of a protein, opsin, joined to a light-absorbing molecule, retinal, which is made from vitamin A.
In the dark:
• Na+ channels in the rod cell membrane are open and Na+ flows in
• the rod cell is depolarised (about −40 mV)
• it continuously releases the neurotransmitter glutamate onto a bipolar neurone
• glutamate inhibits the bipolar neurone, so no impulses are sent along the optic nerve
In the light:
• retinal absorbs light and changes from cis-retinal to trans-retinal
• rhodopsin breaks down into opsin and trans-retinal (bleaching)
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Key terms in this lesson
- visual acuity
- The ability to distinguish fine detail; the sharpness of vision.
More in Mammalian Nervous System
- Cobra Venom
- Sensory Receptors
- The Human Eye
- The Retina
- Cones
- Colour Vision
- Formation of the Brain
- Major Areas of the Brain
All 38 lessons in Mammalian Nervous System · All Edexcel A-level Biology topics