Coordination2
- 2. Sense Organs • Parts of the body that detect stimuli (receptors) Definition: groups of receptor cells responding to specific stimuli: light, sound, touch, temp. and chemicals. • Eye – vision • Ear – hearing and balance • Nose – smell • Tongue – taste • Skin – touch, temperature and pain
- 3. Eye • Eye is a sense organ. • Rod and cone cells in the retina are receptors. Sensitive to light. • Protected by a bony socket in the skull (orbit). Completely surrounded by bone except for the front. • Conjunctiva – a thin, transparent membrane, to protect Tear glands keep this membrane moist and contain an enzyme lysozyme to kill bacteria. Blinking spreads the fluid across the eye
- 4. Eye (cont.) • Eyelids, eyebrows and eyelashes help stop dirt/dust landing on the eye. • Sclera protects inside part of the eye. • Retina - (back of the eye) Receptors receive light Send electrical impulses to brain Along optic nerve Brain creates image
- 5. Retina (cont.) • Fovea – tightly packed with receptor cells which focus an image when we look straight at an object • Blind spot – part of retina where the optic nerve leaves (NO RECEPTORS), light falling on this area won't send impulses to the brain (we can't see) • Chloroid – absorbs the light passed through the retina
- 6. Rod and Cone receptors • Two kinds of receptors in the retina • Rod sensitive to dim light (not colour) • Cone distinguish between colours (bright light) 3 types of Cone for red, blue and yellow. Fovea contains almost mainly cone – meaning we can focus an image Further out in retina rods, show less detailed images. In darkness we can see in black and white in less detail.
- 7. Rods Cones Number in the retina 120 million 7 million Where concentrated Outer edges of the retina The fovea Work best in Dim light Bright light
- 8. Iris • Iris is circular piece of tissue in front of the lens. Coloured part • The gap is the pupil • Adjusts to allow more/less light through to the retina • Strong light = smaller pupil • Why? • To stop too much light damaging the retina
- 9. How does iris adjust size? • Iris contains muscles • Circular muscles around the pupil contract – makes pupil smaller (constrict) • Radial muscles around the edge contract – makes pupil larger (dilate) • Iris reflex • Reflex action – we don't need to think about this action. Our brains do it automatically • What are the advantages of this reflex action?
- 11. Cornea - Refracts light - bends it as it enters the eye Iris - Controls how much light enters the pupil Lens - Focuses light onto the retina Retina - Contains the light receptors Optic nerve - Carries impulses between the eye and the brain
- 13. Focusing light • The lens can change its shape to focus near and distant objects. This is called accommodation. • Accommodation – the change of the shape of the lens, in order to focus on objects at different distances. • Position of object Ciliary muscles Suspensory ligaments Muscle tension on lens Lens shape • Near Contract Slackened Low Fat • Distant Relax Stretched High Thin