Module 1
1. Module 1
1.23. Page 5
Module 1—The Nervous System
Touch
Read
You are about to be introduced to a new student in your school. The room is so hot, and your hand is so sweaty that it feels sticky. When you reach out to shake hands, your realize that this girl has a firm handshake. Your brain tells you that the finger you sprained in basketball practice is hurting from the pressure of the handshake. You wince in pain and pull away quickly. To understand more about touch, read pages 427 to 429 in the textbook.
The mechanoreceptors for touch are located all over the body, but they aren’t evenly distributed. Consider how sensitive your fingertips and lips are in comparison to the back of your hand. Your fingertips and lips can detect light touch, pressure, pain, and high and low temperatures. In the previous activity, when you put your hand in ice water and held it there, it wasn’t long before you felt the freezing sensation. How would it feel if you put your elbow in the ice water? Do you think you could keep your elbow in the ice water longer than your hand?
Sensory Receptors in the Skin
Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 429, fig. 12.27. Reproduced by permission.
In the graphic above, the structure labelled “free nerve endings” is a free dendrite ending found in thermoreceptors (temperature receptors) and some pain receptors. The remaining structures have enclosed dendrites in capsules. These sensory receptors are mechanoreceptors that sense touch, pressure, vibration (on and off pressure), and stretch stimuli. The Krause end bulbs, shown on the left, and Meissner corpuscle, shown at the top right, are sensitive to light touch but are located in different parts of the body.
From the diagram, can you hypothesize which type of receptor is more concentrated in your hand than in your elbow? Does this explain why your hand was more sensitive to the cold water than your elbow was?
Try This
TR 2. Bend a paper clip into a U-shape with the two ends about 2 mm apart. Close your eyes, and gently push the open ends of the paper clip into the palm of your hand. Then, gently press the paper clip against your shoulder and your elbow. In which location could you distinguish the two prongs as being separate?
What do your results suggest about the number of mechanoreceptors for touch in the palm of your hand in comparison to the number in your shoulder? You might want to look at “Figure 12.27” on page 429 in the textbook to review the various types of touch receptors.
Self-Check
SC 12. Complete this receptor table.
Module 1: Lesson 4 Assignment
You will complete a lab as part of your Lesson 4 Assignment.
Lab
In this lab you will develop your own experimental design to study one of the senses. You may choose to study taste, smell, touch, or temperature.
Retrieve the copy of the Module 1: Lesson 4 Assignment that you saved to your computer earlier in this lesson. Complete the assignment. Save your completed assignment in your course folder. You will receive instructions about when to submit your assignment to your teacher later in this lesson.