Touch

Question 1

What are 2 things that are distinct about touch in comparison to the other senses?

Answer 1

1. Receptors for touch are distributed throughout the entire body, whereas other sense’s receptors are confined to specific locations
2. Receptors controlling touch respond to many different types of stimulation and the quality of these sensations in extremely diverse

Question 2

What 2 receptors mediate temperature?

Answer 2

1. Kraus end bulb
2. Free nerve ending

Question 3

What are mechanoreceptors?

Answer 3

The receptors that respond to pressure/indentation of the skin

Question 4

Where are mechanoreceptors located?

Answer 4

The smooth, hairless portions of the skin found on the palms/fingers/soles of the feet (glabrous skin)

Question 5

What are the 4 main types of mechanoreceptors? MR PM

Answer 5

1. Meissner corpuscles
2. Ruffini endings
3. Pacinian corpuscles
4. Merkel discs

Question 6

How many mechanoreceptors are found on the hairless skin on the hand?

Answer 6

17,000

Question 7

What are temporal properties of afferent fibers?

Answer 7

Slowly adapting fibers respond continuously to a persistent stimulus and rapidly adapting fibers respond only to the onset and termination (i.e. a changing) of a stimulus.

Question 8

What are spatial properties of afferent fibers?

Answer 8

Receptive fields in the skin have a concentric organisation (e.g. excitatory centre and inhibitory surround).

Some fibers have large receptive fields and others small receptive fields.

Question 9

What shape is the vibration sensitivity of a Pacinian corpuscle? What is its sensitivity greatest at?

Answer 9

U-shaped. 250 Hz.

Question 10

What are 4 properties of the Pacinian corpuscle?

Answer 10

1. Largest
2. Least numerous
3. Most deeply located
4. Most well studied

Question 11

How are absolute thresholds for passive touch measured? What were the findings?

Answer 11

By recording minimum force necessary to detect a fine nylon filament. Findings showed that 0.001mm can evoke a pressure sensation (Verillo, 1975).

Question 12

Where is absolute sensitivity best?

Answer 12

The face.

Question 13

Where is the two-point localisation threshold lowest?

Answer 13

Hands, feet and face.

Question 14

What information about touch carried by?

Answer 14

Large, fast, myelinated afferent fibers

Question 15

What is information about pain/temperature carried by?

Answer 15

The spinothalamic tract

Question 16

Where in the brain is touch processed?

Answer 16

Somatosensory cortex

Question 17

Areas with what function have larger amounts of neural tissue in the brain?

Answer 17

Areas that are important for the survival of the species.
(In humans: hands/lips/tongue)

Question 18

What % of judgements were correct and how long did it take for participants to make them in Klatsy et al.’s (1985) study of blindfolded participants handling objects?

Answer 18

95%. 5s.

Question 19

Information from the skin’s touch receptors is combined with information from _______ in the muscles and joints which encode the postures, locations and movements of the body.

Answer 19

Proprioceptors.

Question 20

How many words per minute do experience Braille readers achieve? (Foulke & Berla, 1984)

Answer 20

100 or more.

Question 21

Why is it easier to read text written in Braille rather than Roman letters?

Answer 21

Loomis (1981) showed that this is due to the limited ability of the skin to figure out fine spatial details (mechanical properties of skin cause ‘blurring’).

• Tactile stimuli deform not just the area of skin touched but neighbouring regions as well
• This mechanical blurring (loss of high frequency information) has a differential affect upon embossed Roman letters and Braille characters
• Different Roman letters are often distinguished by small differences between the fine lines of which they are composed. Braille made from coarse elements (dots) changed little by blur

Question 22

What can greatly influence the intensity/quality of pain?

Answer 22

Psychological factors (eg. attention/emotional state)

Question 23

What is the evolutionary benefit of pain perception?

Answer 23

The adaptive avoidance of environmental situations that are harmful to the organism.

Question 24

What is the evolutionary benefit of pain perception?

Answer 24

The adaptive avoidance of environmental situations that are harmful to the organism.

Question 25

What is the type of receptor that is stimulated to induce pain?

Answer 25

Nociceptor.

Question 26

What type of receptor is thought to be a nociceptor? Why?

Answer 26

Free nerve endings.
This is because:
- They are the most common type of skin receptor
- They are also found in muscles/tendons/joints
- They are found wherever ‘pain spots’ are located

Question 27

What are 3 properties of afferent ‘pain’ fibres?

Answer 27

1. High-threshold, small diameter, slow-conducting, thinly myelinated or unmyelinated fibers
2. Slow conduction velocity unimportant (once tissue damage occurs it’s already too late)
3. Large receptive fields (amount of damage more important than fine discrimination)

Question 28

Who developed gate-control theory?

Answer 28

Melzack & Wall (1965, 1988)

Question 29

What is gate-control theory?

Answer 29

1. Fast ‘touch’ fibres and slow ‘pain’ fibres connect with substantia gelatinosa (SG) and transmission cells (T cells) in spinal cord
2. T cells send pain information to the brain
3. SG acts as “gate” to allow or inhibit T cells

Question 30

Activity in ___ fibers tends to close the gate (touch but no pain) and ____ fibers open the gate (pain)

Answer 30

fast, slow.

Question 31

Why are we advised to rub our skin to alleviate pain?

Answer 31

A light touch accompanying a noxious stimulus partially closes the gate (reduces pain).