10 Touch and Pain

Question 1

Q: What is the largest sense organ in the body?

Answer 1

A: The skin is the largest sense organ in the body.

Question 2

Q: What are the two types of skin?

Answer 2

A: There are two types of skin: glabrous, found on the palms of hands and soles of feet, and hairy, found everywhere else on the body.

Question 3

Q: Describe the physiology of skin sensation.

Answer 3

A: When a stimulus contacts the skin, receptors in the skin fire, and the signal travels to the brain via the spinal cord, ultimately reaching the somatosensory cortex on the opposite side of the body.

Question 4

Q: What are the four senses associated with skin sensation?

Answer 4

A: The four senses associated with skin sensation are touch (mechanical stimuli), pain, body sense (proprioception), and temperature.

Question 5

Q: What are the four types of tactile receptors in the skin?

Answer 5

A: The four types of tactile receptors are Merkel’s discs (fine details), Meissner corpuscles (flutter), Ruffini organs (stretching), and Pacinian corpuscles (vibration, fine texture).

Question 6

Q: Why are there multiple types of tactile receptors?

Answer 6

A: Multiple types of tactile receptors allow for the detection of various types of information, and a single stimulus can activate many receptor systems.

Question 7

Q: What is meant by receptive fields in the skin?

Answer 7

A: Receptive fields are the areas of skin that a particular cell receives information about. Pacinian corpuscles have larger receptive fields than Meissner’s corpuscles.

Question 8

Q: What is two-point discrimination?

Answer 8

A: Two-point discrimination is the smallest separation of two separate but adjacent points of stimulation on the skin that produces two distinct impressions of touch.

Question 9

Q: How does two-point discrimination vary across different areas of the body?

Answer 9

A: Two-point discrimination is most sensitive on the fingertips, with a threshold of around 2mm, while on the arm, it is around 3.5cm. This difference is due to the number of receptors and the amount of cortex in the somatosensory cortex.

Question 10

Q: What is the homunculus?

Answer 10

A: The homunculus is a representation of the human body in the brain, with areas of the body that are most sensitive taking up the most space in the somatosensory area.

Question 11

Q: What is the significance of fingertip sensitivity?

Answer 11

A: Fingertips have a high density of receptors, making them the “fovea” of the skin, and acuity can change with experience.

Question 12

Q: What is the difference between active touch and passive touch?

Answer 12

A: Active touch involves active exploration of the environment, while passive touch occurs when the body is stationary.

Question 13

Q: What are the advantages of active touch?

Answer 13

A: Active touch allows more parts of the body to contact the object, enables searching for the most diagnostic parts of the object, and engages kinesthetic senses.

Question 14

Q: How do we perceive texture through touch?

Answer 14

A: We perceive texture through spatial cues (bumps and grooves when the finger is stationary or moving) and temporal cues (only when the finger moves across a surface).

Question 15

Q: Which tactile receptors are involved in perceiving texture, and how can their function be impaired?

Answer 15

A: Pacinian corpuscles are involved in perceiving texture, especially through adaptation to high-frequency vibrations. Their function can be impaired by adaptation to these frequencies.

Question 16

Q: What does the “What” and “Where” processing refer to in tactile perception?

Answer 16

A: “What” processing refers to identifying objects by touch, and “Where” processing refers to spatial processing of the location of objects.

Question 17

Q: What is tactile agnosia?

Answer 17

A: Tactile agnosia is the inability to identify objects by touch, while spatial processing remains intact.

Question 18

Q: What does tactile extinction involve?

Answer 18

A: Tactile extinction involves problems in object recognition by touch.

Question 19

Q: What brain areas are active when processing “What” and “Where” tactile information?

Answer 19

A: “What” object processing activates the primary and secondary somatosensory cortex, while “Where” object processing activates the superior parietal areas.

Question 20

Q: How do top-down influences affect touch perception?

Answer 20

A: Top-down influences require updating as the body moves, and the same sensation can be perceived differently based on emotional effects, expectations, and surprises.

Question 21

Q: Why can’t you tickle yourself effectively?

Answer 21

A: You can’t tickle yourself effectively because you can predict the consequences of your own actions, making the sensation less ticklish.

Question 22

Q: What is Aristotle’s illusion?

Answer 22

A: Aristotle’s illusion occurs when you cross your middle and index finger and run them down your nose, making you perceive two separate objects.

Question 23

Q: What is the cutaneous rabbit illusion?

Answer 23

A: The cutaneous rabbit illusion is the perception of evenly spaced jumps when a stimulus involves widely repeated taps on the skin, leading to activity in the primary somatosensory cortex as if the intermediate points had been stimulated.

Question 24

Q: What was the old view of pain?

Answer 24

A: The old view considered pain to be an overstimulation of any sensory system.

Question 25

Q: What is a nociceptor?

Answer 25

A: A nociceptor is a pain receptor.

Question 26

Q: What are the two types of pain fibers and their functions?

Answer 26

A:

A delta fibers: Fast pain (sharp), responding to pin pricks, pinches, and extreme temperatures.
C fibers: Slow pain (dull), responding to various types of pain; mild stimulation can be pleasurable.

Question 27

Q: How can pain be affected by factors beyond receptor activity?

Answer 27

A: Pain can be influenced by mental state, can occur in the absence of a stimulus, and can be affected by attention.

Question 28

Q: What is the gating theory of pain in the spinal cord?

Answer 28

A: The gating theory suggests that the degree to which painful information reaches the brain can be influenced by non-painful tactile inputs (like massage) and top-down inputs (like expectations).

Question 29

Q: What are phantom limbs, and what do they indicate about the brain?

Answer 29

A: Phantom limbs are sensations felt in a limb that has been amputated, indicating that the missing limb is still represented in the brain.

Question 30

Q: What is proprioception?

Answer 30

A: Proprioception is the sense of where your body is in space, relying on signals from muscles, the vestibular system, and tactile receptors.

Question 31

Q: What is kinesthesis?

Answer 31

A: Kinesthesis is the sense of movement of limbs in space.

Question 32

Q: Who is IW, and what did he lose and learn?

Answer 32

A: IW is a man who lost proprioception, kinesthesis, and touch due to a viral infection at 19 but learned over three years to compensate using visual information. He lost fast myelinated fibers but retained slow C fibers.

Question 33

Q: What was significant about the new receptor found in 2002 related to patients like IW?

Answer 33

A: The new receptor indicated that patients who lost other senses of touch could still feel pain, temperature, and enjoy being cuddled, pointing to the existence of CT fibers.