Vision Sensory Receptor What is a sensory Receptor? All sensory receptors operate on the same basis: Stimulus: is detected by the receptor cell and triggers a change in the receptor membrane. Sensory Systems Animal senses range in complexity. Simple nerve endings to complex sense organs. The sensory system present in any particular species are appropriate to its environment to survive. The purpose of the eyes as one of the senses Our world is made up of energy Light/heat Movement/Sound Odours/Taste The light sensory receptors detect light in a given environment. Types of Eyes Light Orientating Eyes: •Found in protozoan (single celled), flatworms, polychaete worms and sea jellies (Cnidaria). •Eye spots / Ocellus •Pigment cup – if light enters front of pigment up – worm turns 180 degrees to sheild eyes •Contain soft lens Types of Eyes Image Forming Eyes: •Octopuses •Lens refracts light rays from a point source and form a single point on the retina •Good image quality – same as other fish Types of Eyes Compound Eyes: •Flies, bees, crustaceans •Resolves images as good as human eye •Very sensitive to movement and flickers – disrupts vision of light •Objects close together cannot be distinguished Types of Eyes The vertebrate eye: •Light enters through cornea •focused by the lens •Produces image on the retina VISION Compound eyes Image forming eyes The vertebrate eye The Advantages and Disadvantages of the Compound Eye The biggest advantage to being an insect has to do with their field of view. Insects, such as the dragonfly, have extremely large eyes, which can see in every direction except for the blind spot created by their bodies. They can also have a dual-vision system, which means that they can see both dark and light, and colour. This can be seen in pollinating insects, such as bees, which rarely get a mature flower mixed up with a maturing or dying one. Unfortunately, insects do not have the best resolving power in the animal kingdom. One degree of arc of a human eye resolving at 1 meter can make out many details of a human hand, whereas a similar portion of an insect eye at its best resolution, looking from the same distance, can only make out an outline of the hand The Advantages and Disadvantages of Octopus and Squid Eyes There are a couple of advantages and disadvantages of possessing the eyes of squids and octopuses. The first advantage of the eye is that it has no blind spot. This means that squids and octopuses can see everything that is going on in their environment, and are more aware of predators and prey than some vertebrates. Also, have many more photoreceptors than vertebrates, at roughly 20,000- 50,000/mm2 which means that their vision is much better than any human. The disadvantage of the squid and octopus eye is that it can not see in colour. The eyes possess no cones, only the vertebrate equivalent of rods. This means that squids and octopuses can only distinguish between light and dark QUIZ Write down your answers: A stimulus is detected by receptor cell Q) How does a sensory receptor work? producing an electrical response. Q) What is a sensory system? Is made up of sensory receptors that are receptive to a specific stimuli. Q) What are the four main types of eye? Give an example of an animal with that eye. 1.Light orientating eye (Cnidarians –sea jellies) 2.Compound (insects) 3.Image forming (Octopus) 4.Vertabrate (human) The vertebrate eye • Function and Structures • How does vision work. • How do we see colour? For vision to occur • Light reaching the photoreceptor cells must form an image on the retina. • This happens when light passes through the pupil. •Refraction (bending) of incoming light occurs with the Cornea. The lens adjusts the degree of refraction to produce a clear image. • The How we see colour • The Retina contains two types of photoreceptors: CONES & RODS • Rods are more sensitive to light (they give us our night vision) however they are not receptive to colour. • Cones are receptive to colour in ample light and are only present Fovea. • There are three different types of cone cells. One is receptive to RED another is receptive to GREEN, the third to BLUE Cone and Rod cells Spots Spots Spots Spots SUMMARY What two functions does the cornea serve? What is the function of the Iris? What happens at the Fovea? What photoreceptor cell is stimulated by colour? What is the blind spot? Write your answers down to the following questions. What are Rod and Cone cells? What is the function of the Lens? What is happening to your vision when you place yellow cellophane over your eye’s? What is the purpose of the Sclera? What colour is it?