Module 1 Lesson 1 - 4
Completion requirements
Lesson 1 — Sensory Perception
Somatosensation - Touch (pages 427-429)
The mechanoreceptors for touch are all over the body, but they are unevenly distributed. Consider how sensitive your fingertips and lips are compared to the back of your hand. The fingertips are more sensitive because the mechanoreceptors are more concentrated
in the fingers than on the back of the hand. Mechanoreceptors can detect light touch, pressure, pain, and high and low temperature.
Image 1 -
Inquiry into Biology Figure 12.27 p.429, from McGraw Hill. Reproduced by permission.
Inquiry into Biology Figure 12.27 p.429, from McGraw Hill. Reproduced by permission.
In the previous activity, when you put your hand into the ice water and held it there, you soon felt the cold or freezing sensation. How would it feel if it was your elbow in the freezing water? Do you think you could keep your elbow in the cold water
longer than you could your hand?
There are various types of sensory neurons under the skin (Image 1): thermoreceptors (hot and cold receptors), some pain receptors, and mechanoreceptors that sense touch, pressure, vibration (on and off pressure), and stretch stimuli.
Look carefully at the diagram (Image 1) and note the various forms of receptors on the skin. Can you explain why your hand is more sensitive to cold than your elbow is? Which type of receptor is more concentrated in your hand than in your elbow?
You need to appreciate the types of receptors, but you will not be asked to name or explain their functions.
There are various types of sensory neurons under the skin (Image 1): thermoreceptors (hot and cold receptors), some pain receptors, and mechanoreceptors that sense touch, pressure, vibration (on and off pressure), and stretch stimuli.
Look carefully at the diagram (Image 1) and note the various forms of receptors on the skin. Can you explain why your hand is more sensitive to cold than your elbow is? Which type of receptor is more concentrated in your hand than in your elbow?
You need to appreciate the types of receptors, but you will not be asked to name or explain their functions.
Try This
Bend a paper clip into a U-shape with the two ends about 2 mm apart. Close your eyes, and push gently on the palm of your hand with the paper clip. Then, press the paper clip gently on your shoulder; then, try it on your thigh and on your forehead. In which location could you distinguish the two prongs as separate points?
With a partner, test for the feeling of the two points, allowing your partner to spread the distance gradually until you feel two points distinctly. Measure this distance in each location.
This activity measures tactile acuity, which is the minimum separation needed for the brain to perceive two points as separate points. The less the distance that two points can be perceived separately, the higher the tactile acuity of that area. Areas with higher tactile acuity have more receptors. Depending on the body part, the minimum separation perceived between two points varies. For example, the tactile acuity of the fingertips is 1.8 mm whereas the palm can sense two points at 8.3 mm. The average tactile acuity for shoulders is 38 mm, thigh is 45 mm, and forehead is 20 mm.
What do your results suggest about the number of mechanoreceptors for touch in the palm of your hand relative to the number on your shoulders, for example?