Page 239 - Biology_F5

Biology for Advanced Level Secondary Schools

Meissner’s corpuscle
Merkel’s disc
Pacinian corpuscle
Free nerve ending

FOR ONLINE READING ONLY

Figure 4.21: Structure of the touch receptors

Photoreceptors
These are receptors that detect electromagnetic stimuli such as light. There are two
types of photoreceptors, namely rods and cones. These are found in the retina of an eye
for detecting dim and bright light respectively (Figure 4.22).

Ganglion cell
Conjunctiva Sclera Amacrine cell

Choroid Bipolar cell
Iris
Lens Vitreous humour Fovea Rods
Pupil Blind spot Cones
Cornea Optic nerve
Suspensory Retina Horizontal cell
ligament
Ciliary Extrinsic
muscle
body

Figure 4.22: Structure of the photoreceptors

Form Five Student’s Book
232