Chapter 3- The Somatosensory System: Touch, Feeling, and Pain
Neural Basis of Somatosensory Perception
Touch is distinctive among the senses in that its multiple attributes (pressure, vibration, warmth, cold) can interact to
produce compound sensations (e.g. wetness, sponginess, etc.), having both objective (“where was I touched”) and
subjective qualities (what did I touch/ how did it feel?), and yet they are all part of a single kind of sensory experience.
Touch is also distinctive in that its related receptors are located throughout the whole body.
Historically, 2 main ideas has been proposed to account for the way in which touch signals are generated and
transmitted to the brain:
theory of receptor specificity –
from Johannes Mueller’s doctrine of specific nerve energies, whereby
individual receptors and nerve endings are selectively sensitive to a particular form of energy impinging on
the skin. Max von Frey suggested that there were specific receptors for heat, cold, pressure, and pain.
pattern theory –
in which the specificity of touch sensations was believed to arise not from individual
receptors, but through overall pattern of activity across a broad spectrum of receptors.
I.e. different types of touch generate different patterns of activity, which the brain interprets as a
It has been found that touch signals are indeed highly specific and selectively generated by a particular type of
Although we accept this specificity, most forms of touch involve stimulation of multiple types of
The skin and its receptors
Skin surface area = close to 15 square feet; weighs about 10 pounds.
: closely packed cells that fit together to form continuous sheets found on the surface of the body or in
the lining of its cavities.
Skin tissue is anatomically divided into 2 principal divisions:
Epidermis: outermost layer; serves as a protective shield; composed of several sublayers that are constantly
Dermis: underlying layer; makes up the bulk of skin tissue; contains most of the mechanoreceptors and nerve
endings that generate touch sensations.
Skin tissue can also be broadly classified into 2 general types:
Hairless (palms, lips, etc.)
Types of mechanoreceptors:
Mechanoreceptors can be classified into 3 types:
1. Encapsulated receptors: have a specialized capsule surrounding a nerve ending.
i.e. Pacinian, Meissner, and Ruffini corpuscles.
The capsule itself serves specific functions of the particular type of touch.
i.e. onion-like structure of Pacinian corpuscle acts like a mechanical filter, aiding in transmission of
Meissner- designed for transmitting light touch.