Chapter 13 Study Questions
Touch Physiology
1. Describe the two layers of the skin known as the epidermis and dermis.
Answer: The epidermis is the outermost of the two layers. The dermis is the innermost layer of the two, consisting of nutritive and connective tissue, within which lie mechanoreceptors that respond to pressure and vibration.
2. What are mechanoreceptors?
Answer: Mechanoreceptors are sensory receptors that are responsive to mechanical stimulation such as pressure, vibration, and movement.
3. What are the four types of mechanoreceptors?
Answer: The four types of mechanoreceptors are Meissner, Merkel, Pacinian, and Ruffini receptors.
4. Name and describe the two types of thermoreceptors.
Answer: The two types of thermoreceptors are warmth fibers and cold fibers. Warmth fibers are sensory nerves that respond when skin temperature increases, and cold fibers are sensory nerves that respond when skin temperature decreases.
5. Why are nociceptors important?
Answer: Nociceptors are important because they transmit information about noxious (painful) stimulation that causes damage or potential damage to the skin.
6. What is the role of the muscle spindle?
Answer: The muscle spindle is a sensory receptor located within a muscle that senses its tension. The sensory response from the spindle is sent back to the central nervous system, conveying information about muscle length and thus regulating muscle tension.
7. What are kinesthetic receptors responsible for?
Answer: Kinesthetic receptors are responsible for giving us a sense of where our limbs are, and what kinds of movements we are making.
8. What is the dorsal horn?
Answer: It is a region at the rear of the spinal cord that receives inputs from receptors in the skin. The dorsal horn contains interneurons that perform computations that may provide the sense of touch with its rich canvas of effects, from caresses to pokes.
9. How does tactile information travel from the spinal cord to the brain?
Answer: Tactile information travels from the spinal cord to the brain via two pathways: the spinothalamic pathway and the dorsal column–medial lemniscal (DCML) pathway. The spinothalamic pathway carries most of the information about skin temperature and pain, while the DCML pathway carries signals from skin, muscles, tendons, and joints.
10. How are touch sensations represented in area S1?
Answer: Touch sensations are represented in area S1 somatotopically. This means that the representations are mapped in correspondence to the skin, so that adjacent areas on the skin are ultimately connected to adjacent areas in the brain.
11. What is a homunculus?
Answer: A homunculus is a maplike representation of regions of the body in the brain.
12. What kind of sensation is described by the term “phantom limb”?
Answer: The sensation of a phantom limb is the perceived sensation from a physically amputated limb of the body.
13. What is one possible explanation for the sensation of phantom limb?
Answer: One possible explanation for the sensation of a phantom limb is that certain parts of the brain are not aware of the severed connection between the missing limb and the brain, and therefore they attribute any activity in these areas to stimulation from the missing limb.
14. What is analgesia?
Answer: Analgesia is decreasing pain sensation during conscious experience.
15. What is the role of the endogenous opiates?
Answer: Endogenous opiates are chemicals released by the body that block the release or uptake of neurotransmitters necessary to transmit pain sensations to the brain, thus creating an analgesic effect.
16. What kind of function is the anterior cingulate cortex associated with?
Answer: The anterior cingulate cortex is associated with the perceived unpleasantness of a pain sensation.
17. What kind of function is the prefrontal cortex associated with?
Answer: The prefrontal cortex is associated with cognition and executive control, including memories of pain or anticipation of pain.
Tactile Sensitivity and Acuity
18. What is the two-point touch threshold?
Answer: The two-point touch threshold is the minimum distance at which two stimuli (e.g., two simultaneous touches) are perceivable as being separate.
19. How can two-point touch thresholds be determined?
Answer: Two-point touch thresholds can be determined by the concentration and receptive-field sizes of touch receptors in an area of the skin. This can be done in the laboratory by administrating point stimulators to the subjects, and then observing how different areas of skin respond to the stimulation.
Haptic Perception
20. What are exploratory procedures used for?
Answer: Exploratory procedures are ways in which objects are touched in order to perceive their properties. Each exploratory procedure is best for extracting one or more object properties.
21. What role do fingerprints play in tactile perception?
Answer: They enhance tactile perception by amplifying the vibration frequencies that FA II mechanoreceptors measuring fine surface textures are most attuned to.
22. What is tactile agnosia?
Answer: An inability to recognize objects by touch, resulting from a lesion in the parietal lobe.
23. How does establishing a frame of reference help in haptic object localization?
Answer: Establishing a frame of reference helps in haptic object localization since it defines locations in space. Based on these locations, it is then possible to use haptic perception to perceive the objects.
24. What is a haptic virtual environment?
Answer: A haptic virtual environment is an electromechanical device that allows the user to experience a synthetic world through the sense of touch. The device delivers forces to the hand of the user that simulates the forces that would actually be felt if the virtual environment were real.