Pain
Introduction
Sensation & Sensory Processing
Sensation involves the ability to transduce, encode and ultimately perceive information generated by stimuli arising from both the external and internal environment. A large proportion of the brain is devoted to these tasks.
Despite the diversity of somatic sensation, from audio & visual to vestibular & chemical, the basic mechanisms are common to them all. Highly specialized nerve cells, called receptors, convert specific energy, eg sound, into neural signals [Transduction]. These signals convey information regarding the stimulus to the brain; these afferent signals (from the Peripheral to the CNS) are capable of representing different aspects of the stimulus, both quantitative (how strong) and qualitative (what it is) and sometimes location information too [Encoding]. The areas of the CNS that receive the signals are responsible for the emotional and cognitive processing of the stimulus [Perception]. [5, 32, 40]
The Somatic Sensory System has two major components:
- Detection of mechanical stimuli: eg. Touch, vibration, pressure and tension.
- Pain & Temperature
Together these subsystems allow the identification and monitoring of object
shapes and textures, external and internal forces, and potentially harmful
circumstances. The receptors involved in these processes are: mechanoreceptors,
nociceptors
and thermoreceptors. The latter two are known as ‘free nerve endings’
due to the termination of the unmyelinated nerve endings occurs in the upper
regions of the dermis and epidermis regions of cutaneous tissue. Nociception
is the detection of noxious (painful / harmful) stimuli, nociceptors are specialised
cells to detect these stimuli. [32,
40]
Pain
Pain can be defined as an “unpleasant sensory and emotional experience,
resulting from potential or actual tissue damage, or described in terms of
such damage”.
The level of pain perceived is not linearly connected with the level of damage
sustained; pain perception relies on two facets:
- ‘Sensory-discriminative’ component: This tells you that you have been hurt and where
- ‘Emotional-affective’ component: The association of unpleasant
emotions with the physical stimulus or response.
