Touch and Pain
Somatosenses
They produce information about events occurring on the surface and on the inside of the body
Cutaneous sense - (skin sense) involves touch, pain and temperature
Proprioception and Kinaesthesia - provides sensory information about the body position and movements - stretch receptors
Organic Senses - provide information about pleasant and unpleasant sensations in internal organs
Anatomy of Skin
Consists of subcutaneous tissue, dermis and epidermis. Hairy and glabrous skin controls various receptors of different level. Glamorous skin does not contain hair, found on palms of hands and soles of feet. There are more receptors on glabrous skin as they come into contact with more things.Skin is a vital organ for survival
Skin Receptors also called macanoreceptors
Ruffini corpuscles - responds to indentation of skin- responsible for maintaining grip- adaptation is slow - both hairy and glabrous
Pacian corpuscles - rapid vibration- responsible for detecting roughness or very small vibrations- adaptation is rapid - hairy and glabrous
Meissner's corpuscles - low frequency vibration or tapping - responsible fortune sensitivity like feeling a bug on skin- adaptation is moderate - just glabrous
Merkel's disks - indentation of the skin- responsible for detecting pressure- adaptation is slow- just glabrous
Perception of temperature
Temperature receptors are called thermoreceptors. They have free nerve endings skin. There are two types: warm receptors(signal conveyed in unmyleinated C fibres); cold receptors (signal conveyed in lightly myelinated A delta and unmylinayed c fibres)
Perception of pain
Pain receptors are nociceptors- detect noxious stimuli. They have free nerve endings. pain travels in lightly militated A delta fibres (well localised and brief) and unmylinated c fibres
Types of Nociceptors
High threshold mechanoreceptors - intense pressure i.e. a pinch
Heat sensitive - burning and inflammation
ATP sensitive - reduced tissue blood supply involved in migrane and muscle damage
Somatosensory Cortex
There are two main areas, primary (S1) and secondary (S2) somatosensory cortex. It has a somtopic arrangement which maintains organisation with CNS. Your mouth, tongue and hands have an increased area size compared to the others.
Phantom Limb Pain
Sensation of continues presence of an amputated limb which usually results in severe pain.
Theory of cross wiring - S1 areas near hand (arm/face) take over 're-map' the hand region. Thus stroking the face may be interpreted as sensation in missing limb
Perceptual and behavioural effects of pain
Sensory - (pain intensity) involves pathways up to S1 and S2 cortex
Immediate emotional consequences - (unpleasantness of stimulus) involves insular cortex and anterior cingulate cortex
Long term emotional implications of chronic pain - involves pathways reaching prefrontal cortex.
Pain is subjective
Sensory signal in CNS. Pain perception depends on complex neural interactions where impulses generated by tissue damage and modified by: ascending systems (from peripheral to CNS); Descending systems (sent from brain to peripheral)
Ascending regulation of pain
Modification of afferent information
Gate theory of Pain (Melzack and Wall)
Both tactile and nociceptive fibres synapse projection neurones that carry information to the brain. Noxious input excites projection neurones and therefore more pain. Tactile and noxious input together inhibits projection neurone and therefore less pain
Descending Regulation of Pain
Pain can be reduced by brain in: periaqueductal grey (mid brain)and rostrovential medulla
Endogenous opines are key (internal pain killers) increase periaqueductal grey activity and therefore has a pain killing effect chemical response
Non-Oped anglesia - prequential grey receives inputs from frontal cortex, amygdala and hypothalamus (learning and emotion effect pain)
Psychological factors influencing pain
Early experience (pain memories) - decrease your pain sensitivity in later life
Perceived self-efficiency
Distraction/Attention - attention increases pain and distraction reduces it
Anxiety - increases if stimulus is out of there control
Depression
Perceived helplessness