L3 Touch Flashcards
What are the characteristics of touch perception ?
Part of the somatosensory system
Touch is vital for survival
Receptors for touch are all over the body
Touch can evoke many sensations like roughness, temperature, pain etc
Proprioception - where our body is in relation to the space around us
What are the sensory receptors in mammalian skin ?
- epidermis
- dermis
- merkel’s disk (pressure)
- free nerve endings (pain, temp, pressure)
- meissner’s corpuscle (pressure)
- kraus and bulb (temp)
- basket cell (pressure)
- ruffini ending (pressure)
- pacinian corpuscle (pressure)
What are the characteristics of cutaneous touch receptors ?
Different sensory qualities are mediated by different specialised receptors
Mechanoreceptors respond to pressure
The hairless parts of the body contain many mechanoreceptors
There is no receptor that exclusively evokes a specific touch sensation
What are the temporal and spatial properties of mechanoreceptors/afferent for touch ?
Temporal - slowly adapting fibres respond continuously to a tactile stimulus
Spatial - receptive fields in the skin a concentric organisation, the receptive fields can be large (back) or small (fingertips)
What is the pacinian corpuscle ?
The most well-studied of the mechanoreceptors
Sensitive to touch
Vibration sensitivity is U shaped
Are all regions of the skin surface equally sensitive ?
No
It varies across the body
Two point localisation threshold also varies across the body surface
What is the pathway for somatosensory information ?
Touch information is carried by large, fast, myelinated afferent fibres that enter the dorsal side of the spinal chord
Axons project to the brain stem, cross the midline, and then to the thalamus on the opposite side of the brain
Pain and temperature is carried by spinothalamic tract
Where in the brain is incoming touch information processed ?
Somatosensory cortex receives and processes touch information
Discovered during brain surgery
Most sensitive skin areas are represented by larger areas of cortex
What information is gained from active touch ?
When we touch something our body actively explores objects in the immediate environment
Info from the skins touch receptors combines with info from proprioceptors which encodes postures, locations and movements
What is Braille ?
Tactile pattern alphabet for visually impaired people
It is easier than feeling raised letters as they blue together into similar shapes
What is the significance of pain ?
Pain is subjective
Difficult to assess
Impossible to identify a specific evoking stimulus
Psychological state plays a role - e.g when a rugby player gets injured they don’s notice until after the game because of adrenaline
It is difficult to test due to ethical reasons
Are there specific receptors for pain ?
Pain results from stimulation of a specialised class of receptors called nociceptors (to injure)
They are the most common type of skin receptor
Neural messages from nociceptors are carried by pain fibres that travel to the spinothalamic tract of the spinal cord
What theory explains the variable nature of pain ?
Gate control theory
Fast touch 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 a gate to inhibit T cells
