notes6 - Human Olfaction RECEPTION & INTEGRATION: The...

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1 1 The Nervous System 2 Objectives 1. Describe the origin of the insect nervous system. 2. Identify the major structures of the insect nervous system and describe their function. 3. Compare and contrast the physical structure and functions of compound eyes and simple eyes. 4. Differentiate between the two types of simple eyes. 5. Describe the four types of mechanical receptors insects possess. 3 Introduction Have you ever thought about how insects receive information from their environment? We use our five senses, but what about them? Does an insect have a nose? The answer may seem obvious to you. Insects do not have noses, but have you ever thought about how they smell? Or do they smell? The answer is, yes, they do. They have receptors on their antennae and other parts of their body to pick up scents. In order to understand how an insect "picks up a scent" let's first look at how humans do it. 4 Someone is baking luscious bread in the kitchen. As you walk by the kitchen, chemical molecules mixed with the steam, waft up from the cooking food and enter your nose. The molecules then bind to tiny hairs in the nasal cavity. These hairs are extensions of olfactory (smelling) nerve cells. Nerve cells are also called neurons . The binding of the chemical causes your olfactory nerves to fire and send a message to your brain. There the brain interprets the message and fires another nerve cell in response that stimulates your salivary glands. You begin to salivate and you are ready to eat. Human Olfaction (All this talk about food is making me hungry.) 5 Insect Olfaction Insects smell in a similar way. Their olfactory neurons are not enclosed in a nasal cavity, but within their antennae, mouthparts, or legs. When a female moth sends out a chemical to attract a mate, the male moth picks up the chemical molecules with his antennae where his olfactory neurons are located. These neurons fire a message to his brain which interprets the signals and stimulates neurons that cause the male to fly--migrating toward the female's scent. Antennae of a male moth of Trictena atripalpis : (a) anterior view of the head; (b) cross-section through the antenna showing the antenna is branched three times; (c) enlargement of the tip of one of the branches showing olfactory hairs. 6 Nervous System Development The insect nervous system arises during embryonic development from cells called neuroblasts located in the ectoderm. These neuroblasts first develop into a mass of nerve cells called a ganglion (plural ganglia). Two ganglia form in each segment and they begin to connect with each other as neuron fibers grow out from each ganglion. Representation of nervous system development. (a)
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notes6 - Human Olfaction RECEPTION & INTEGRATION: The...

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