light stimulus
TRANSCRIPT
Receptors A receptor receives information from the
environment. They can be classified according to the type pf
stimulus they respond to.
Receptors are traducers: they convert the Energy of the stimulus into the kind of energy the nervous system can deal with (electrical impulses).
Receptor type Responds to stimulus
Example in humans
Photoreceptor Light Rod cells in retina of eye
Chemoreceptor Chemicals Taste buds
Thermoreceptor Changes in temperature
Thermoreceptors in skin
Mechanoreceptor Mechanical changes Hair cells in ear.
LIGHT STIMULUS:
PHOTORECEPTORS
How living beings sense light?
Unicellular organisms and plants.Photoreceptor pigment inside the cell.
Worms
PlanarianLight sensitive
eyespots (ocelli)
Only sense variations in light´s intensity.
They can detect where the light is coming from.
MollusksDiscriminates simple shapes.
Lens
Sense organ
Receptors may need help in receiving the stimulus. They are often grouped together with other tissues to form a sense organ. The other tissues allow the receptor cells to work efficiently.
Simple eyeProcesses some
images and detects shapes.
InsectsCompound eyes: consists of numerous
separate light-sensitive units (ommatidia). All these images generate an overall picture.
Very useful in detecting movement.
Vertebrates
The position of the eyes is important
Monocular vision
Laterally located eyes: the animal perceives a wide picture of its surroundings.
Binocular vision
Frontally located eyes. 3D imaging allows better asessment of target´s position and field´s depth.
Activity Find the function for the underlined
structures: