Topic: Smell, taste, touch

Author: Elżbieta Szedzianis

Target group

7th‑grade students of an eight‑year elementary school.

Core curriculum

7th‑grade

10. Sensory organs. Student:

5) presents the role of the sense of balance, taste, smell and touch; identifies where the receptors of these senses are, plans and conducts an experiment that checks the closeness of where the receptors are located in the skin on various parts of the body.

Lesson objective

The students describe how the senses of taste, smell and touch work and what their meaning is.

Key Success Criteria

• you will plan and conduct an experiment that investigates how sensitive to the touch the skin is;

• you will talk about the stimuli are registered by the receptors in the skin, in the oral cavity and in the nasal cavity;

• you will explain how the olfactory, gustatory and tactile sensations are created.

Key Competences

• communicating in the mother tongue;

• communicating in a foreign language;

• mathematical competence and basic competences in science and technology; 

• digital competence;

• learning to learn;

• social and civic competences.

Methods/Forms of work

Work with text, experiment, a talk.

Individual work and work in groups.

Teaching measures

• abstract;

• interactive or traditional whiteboard;

• tablets/computers;

• paper clips.

Lesson plan overview (Process)

Introduction

The teacher gives the topic of the lesson, defines the purpose of the course and gives the students the success criteria. The teacher explains the plan to the class.

Realization

1. The teacher asks the students to present the rules of conducting experiments.

2. He divides the students into groups. The task of each group is to plan an experiment that is aimed at checking how frequently skin receptors are located in various parts of the body; in addition, the groups have to formulate a research problem and a hypothesis. The research tool the students will use is an open paper clip.

3. After the teacher gives a positive opinion of the plan of an experiment, the students begin conducting it. They write down their findings and conclusions.

4. Each group presents the results of their work in front of the entire class. They talk about the doubts they had at the planning stage of the experiment, deciding arguments and the issue of the reliability of the results. The other students, while listening to the presentation, share their observations regarding the presentation, but they do not assess them.

5. The teacher asks the students to read the fragment titled “Sensory organs”. He then asks, why a person who is carrying a glass with hot drink, instead of dropping it, can ignore the pain and carry it to where it was supposed to be carried to. The students explain the reason for the lack of unconditioned reflex in that situation. They explain how the information is conducted from the receptor in the skin through the centres in the cerebral cortex to the effectors in the muscles.

6. On the basis of the abstract the students describe the localization and the meaning of the sense of smell and talk about the receptors which are connected with the intake and the tasting of the food.

Summary

1) The students explain why experiments must be planned and why it is worth to discuss about their presuppositions and their results.

2) The teacher asks the students to read the “Summary” and shows three sentences which contain the information that was unknown to them before the lesson.

Homework

The students complete the interactive exercise.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Smell, taste, touch

The organism maintains contact with its surroundings thanks to sensory organs: of sight, hearing, balance, smell, taste, touch and feeling the temperature. Each one of them is focused on receiving different type of information, the so‑called stimuli. There are for example mechanical stimuli (touching something or somebody, a hug, a hit), light (brightness and colour of the light), acoustic (increasing pitch of the sound), chemical, thermal. Sensory organ under the influence of the stimuli received by the sensory cells (receptors) create electric impulses.

Sensory organs are composed of an adequate receptor which is to be found at the border of the body sensitive to a specific type of a stimulus and the sensory nerves which conduct the information from the receptor to the encephalon (very often through the spinal cord). The interpretation of the information received takes place in the cerebral cortex. Because of this, a person who suffers from damaged visual cortex (e.g. after an injury to the back of the head), can stop seeing, even thought the eyes and optic nerves function correctly.

In the air there are numerous chemical compounds floating around and getting into our nasal cavity. In its upper part there is the olfactory epithelium, whose receptor cells (sensory cells) become stimulated when certain chemical compounds are present. Collections of particles of various type and of various composition cause different olfactory sensations.

The molecules of the substances are dissolved in the water that is in mucus produced by the mucous membrane cells. In order to stimulate the olfactory receptors, chemical substances must fit them in shape. They connect to the receptor, which causes a neural impulse. Neural stimulation is transferred via sensory nerves (olfactory) to centres in the cerebral cortex where olfactory sensation is created.

Chemical stimuli in the form of chemical compounds present in food we eat are received not only by olfactory cells, but also by gustatory cells. They are found mainly on the top surface of the tongue, on the palate and in the throat.

With an unaided eye you can see them on the tongue, where they form small protrusions called gustatory papillae. Each of them has around 200 taste buds. A single taste bud is a cluster of gustatory cells which react only to the chemical compound particles dissolved in the saliva of the oral cavity. Each gustatory cell has the ability to react only to one of the 5 basic flavours: salty, sweet, sour, bitter and umami (savory). Sweet flavour is associated by the majority of us with something pleasurable. Developing sensitivity to that flavour allowed people to select ripe, nutritious fruit. Umami flavour, so attractive to many people, is connected with protein food that is high in calories and was a reward for hunters who gained nutritious food that saved people from hunger. Bitter flavour is mainly seen as unpleasant, which is characteristic for many toxic substances and which warns us of possible dangers.

Particles of the substances that are in the oral cavity dissolve in water that is in saliva. This is the only time when the gustatory cells can be stimulated and neural impulses are created. They travel through sensory nerves to the centres in the cerebral cortex. Each impulse arriving from a single gustatory cell overlaps each other in the cerebral cortex and creates gustatory sensation.

Gustatory organs and organs of smell receive chemical stimuli and take an important part in the assessment of the quality and freshness of food we eat. They have a very important role for the body - they protect it, because they inform the body of the presence of dangerous substances in the environment.

Sense of touch is represented by numerous receptor cells found in skin and, for example, inside our oral cavity and at the surface of the eye. From the environment, they receive mechanical stimuli identified as touch, pain, pressure. They are not evenly distributed on the surface of the skin. Most sensitive to stimuli are lips, fingertips, bottoms of the feet and palms. Neural impulses that are created in receptor cells of the skin are transferred to sensory centres in the cerebral cortex.

Besides tactile cells, skin also has receptors of sensing warmth and cold. They are sensitive to all changes of the temperature of the environment. Feeling of cold and hot is relative. When we put one hand to warm water and the other to cold water, and then we put both hands into a container with lukewarm water, the sensation coming from one hand will have the content “cold water”, whereas the sensations coming from the other hand will say “warm water”.

• The organs of smell and taste are responsible for receiving chemical stimuli.

• Sense of smell is composed of sensory cells in the olfactory epithelium of the nasal cavity.

• The main organ of taste is the tongue, on whose surface we have the taste cells.

• Organs of the sense of taste and smell work with each other in feeling the taste of the food we eat.

• Only those chemical substances which were dissolved in water can release a neural impulse in the receptor cells of the nasal cavity and of the tongue.

• In the skin there are receptors which react to pain, touch, warmth, cold and pressure.

• Receptors are unevenly distributed depending on which part of the body they are on.