Touch Flashcards
What are 2 things that are distinct about touch in comparison to the other senses?
- Receptors for touch are distributed throughout the entire body, whereas other sense’s receptors are confined to specific locations
- Receptors controlling touch respond to many different types of stimulation and the quality of these sensations in extremely diverse
What 2 receptors mediate temperature?
- Kraus end bulb
- Free nerve ending
What are mechanoreceptors?
The receptors that respond to pressure/indentation of the skin
Where are mechanoreceptors located?
The smooth, hairless portions of the skin found on the palms/fingers/soles of the feet (glabrous skin)
What are the 4 main types of mechanoreceptors? MR PM
- Meissner corpuscles
- Ruffini endings
- Pacinian corpuscles
- Merkel discs
How many mechanoreceptors are found on the hairless skin on the hand?
17,000
What are temporal properties of afferent fibers?
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.
What are spatial properties of afferent fibers?
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.
What shape is the vibration sensitivity of a Pacinian corpuscle? What is its sensitivity greatest at?
U-shaped. 250 Hz.
What are 4 properties of the Pacinian corpuscle?
- Largest
- Least numerous
- Most deeply located
- Most well studied
How are absolute thresholds for passive touch measured? What were the findings?
By recording minimum force necessary to detect a fine nylon filament. Findings showed that 0.001mm can evoke a pressure sensation (Verillo, 1975).
Where is absolute sensitivity best?
The face.
Where is the two-point localisation threshold lowest?
Hands, feet and face.
What information about touch carried by?
Large, fast, myelinated afferent fibers
What is information about pain/temperature carried by?
The spinothalamic tract
Where in the brain is touch processed?
Somatosensory cortex
Areas with what function have larger amounts of neural tissue in the brain?
Areas that are important for the survival of the species.
(In humans: hands/lips/tongue)
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?
95%. 5s.
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.
Proprioceptors.
How many words per minute do experience Braille readers achieve? (Foulke & Berla, 1984)
100 or more.
Why is it easier to read text written in Braille rather than Roman letters?
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
What can greatly influence the intensity/quality of pain?
Psychological factors (eg. attention/emotional state)
What is the evolutionary benefit of pain perception?
The adaptive avoidance of environmental situations that are harmful to the organism.
What is the evolutionary benefit of pain perception?
The adaptive avoidance of environmental situations that are harmful to the organism.
What is the type of receptor that is stimulated to induce pain?
Nociceptor.
What type of receptor is thought to be a nociceptor? Why?
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
What are 3 properties of afferent ‘pain’ fibres?
- High-threshold, small diameter, slow-conducting, thinly myelinated or unmyelinated fibers
- Slow conduction velocity unimportant (once tissue damage occurs it’s already too late)
- Large receptive fields (amount of damage more important than fine discrimination)
Who developed gate-control theory?
Melzack & Wall (1965, 1988)
What is gate-control theory?
- Fast ‘touch’ fibres and slow ‘pain’ fibres connect with substantia gelatinosa (SG) and transmission cells (T cells) in spinal cord
- T cells send pain information to the brain
- SG acts as “gate” to allow or inhibit T cells
Activity in ___ fibers tends to close the gate (touch but no pain) and ____ fibers open the gate (pain)
fast, slow.
Why are we advised to rub our skin to alleviate pain?
A light touch accompanying a noxious stimulus partially closes the gate (reduces pain).
