A ray of light enters the retina, and a signal leaves it…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A ray of light enters the retina, and a signal leaves it.
- In what order does the ray meet the three layers of cells, starting on the side of the vitreous humour?
- In what order does the signal pass through the cells to reach the optic nerve?
- Which layer holds the rods and the cones?
- A tiny object forms its image on the blind spot. Why is it not seen?
Need a reminder? The key ideaShow
The eyeball has three layers: the sclera (with the cornea), the choroid (with the ciliary body and the iris) and the retina. The lens is held by ligaments of the ciliary body. The aqueous humour lies in front of the lens, and the vitreous humour lies behind it. The retina has ganglion cells, bipolar cells and photoreceptor cells from inside to outside. The area of a circle is .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The ray meets the ganglion cells, then the bipolar cells, then the photoreceptor cells, from the inside to the outside.
Step 2. (b) The signal goes the other way: photoreceptor cells, bipolar cells, ganglion cells, then the optic nerve.
Step 3. (c) The photoreceptor cell layer, which is the outermost layer of the retina.
Step 4. (d) The blind spot has no photoreceptor cells, so it cannot sense light. The object is not seen.
Answer: (a) ganglion, bipolar, photoreceptor; (b) photoreceptor, bipolar, ganglion, optic nerve; (c) the photoreceptor layer; (d) no rods or cones there.
Watch out. The light does not meet the photoreceptors first. It passes the other two layers.
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