Chapter 2. The Senses 2.1 Sensory Receptors (p.25-27) sensory receptors - specialized nerve cells whose function is to collect information about changes in the surrounding environment. sensory organs - specialized body parts where similar types of sensory receptors are especially concentrated in order to receive information about a particular type of environmental change. Because one sensory organ (e.g. eye) responds to a different stimulus from another (e.g. nose); the types of nerve cells differ between the two organs as well! stimulus - a change in the environment that is detectable by one of the senses. nerve cells - specialized cells which carry electrical messages from one place to another NERVE STRUCTURE - nerves - a bundle of many nerve cells which carry messages over large distances response - an action which is a result of a sensed stimulus. Stimulus Sensory Receptor Nerves Brain Response food aroma aroma received impulse impulse mouth by nose transferred sensed waters to brain (interpreted) 2.2 Structure of the Eye 1
Read p. 28 and 29 Draw and label p. 29 Figure 2.6 Labels to include function of the particular part (from text reading) Must be neat Separate page 2
Eye protection Because your eyes are both important and delicate, they have a number of protective structures. 1) Encircling bones of skull - against impact with large objects. 2) Eyelids - against small objects and refreshing of protective moisture coat. 3) Eyelashes - a screen against dust, small particles. 4) Eyebrows against falling dust, particles and perspiration. 5) Tear glands - supplies moisture and a wash for fine particles. The importance of extra protection - (students to write short paragraph can refer to Figure 2.10 for ideas.) 2.3 Vision All the eye does is collect light, and turn it into electro-chemical impulses. It cannot see on its own. How do we see? What would happen if the area of the brain responsible for interpretation was killed? Rods And Cones rods - dim light sensitive; for dim or night vision. Need Vitamin A for maintenance. Night blindness - when eyes adjust too slowly to dim light cones - bright light sensitive. Three types: red stimulated green stimulated blue stimulated Depth of Field 3
Images produced from each eye are slightly different. The blending of these two images produces a 3D effect. Blind aides Read p. 35-36 Describe 3 aids for the visually impaired. Activity 2C 4
2.4 The Ear The ear is divided into three parts: outer ear auditory canal - a tube running from the exterior into your head. ear drum - thin membrane stretched over the inner end of the canal. middle ear hammer, anvil and stirrup - three bones connected in series inner ear cochlea - a spiral, fluid-filled tube which has tiny hairs each one connected to a sensory receptor. auditory nerve - a nerve leading from the cochlea to the brain which carries impulses produced by stimulated sensory receptors. How something is heard: 5
Causes of hearing loss 1) sharp sounds (vibrations) over 120 db 2) repeated sounds (vibrations) over 85 db 3) birth defect 4) ear infection 5) foreign body damage of eardrum (pencil in the ear) See Table 2.1 Why do you suppose your Mom rags on you for listening to loud music, especially through headsets? Review 2.4 2.5 Chemical Detection: Taste and Smell Taste Read p.45-46 Draw Figure 2.28 and 2.29 The sense of taste is limited only to what is placed in the mouth, and only to what is dissolved in water. There are four basic types of tastebuds which are more highly concentrated in distinct areas of the tongue bitter salt sour sweet Tastebuds decrease with 6
age (wear and tear) eating very hot or spicy foods smoking Smell Sensory receptors in nasal cavity often work in conjunction with taste buds to allow the brain to better interpret the identity of a food item. Activity 2E 2.6 Skin The skin is supplied with five different types of receptors: 1) touch - tells when contact has been made with a foreign object 2) pressure - tells degree of weight on the body 3) heat - 4) cold - 5) pain - The number of each type of receptor in a given part of the body depends on what type of function or job the part has; finger tips have lotsa touch receptors. Draw figure 2.32 and label 7