Thermoreceptors There is a wonderful graph on page 251 that indicates the sensitivity of temperature receptors in humans. We have cold receptors that detect temperatures from 15 C to 35 C, peaking at about 25. These detectors go silent and then again respond to temperature above 45 C with tremendous bursts of firing. Warm detectors detect from about 24C, peak at 37 and quit at 45. Photoreception Page 257 has a good sketch of the eye and page 259 has a pretty good picture of a mammalian light receptor.
Rods have an outer segment attached to the cell body by a modified cilium.
The outer segment is composed of tightly stacked disks of membrane much like Pringles in a can. In this case, the can and potato chips are composed of the same material and in some places one can see that they merge and that the membrane stacks are composed of infoldings of cell membrane that do not always completely separate from it. The disks form at the base of the outer segment, migrate up the cell and are devoured by the pigment cells from the end of the rod cell. The inner segment is loaded with mitochondria and contains the nucleus and a synaptic body with vesicles of neurotransmitter and synaptic ribbons. The outer segment is often embedded in a pigment cell which can phagocytize the end of the rod.