Receptors in Skin

The Structure and Function of the Pacinian Corpuscle as an example of transduction of mechanical to action potentials

Properties of Skin Receptors Related to Touch

Various Touch Receptors Responding to Braille

Table 8.2 Fibers That Link Receptors to the CNS

Somatosensory Pathways

Representation of the Body Surface in Somatosensory Cortex (Part 1)

The Columnar Organization of the Somatosensory Cortex

Doesn’t That Hurt?

The Multifaceted Character of Pain

Peripheral Mediation of Pain

Receptors That Detect Pain and Temperature

Pain ascends the spinothalamic system to reach the brain

Synapse here

Ascending and Descending Pain Pathways

Filelds et al Nature NeuroscienceReviews 2004

STATE-DEPENDENT OPIOID CONTROL OF PAINFields et al Nature Neuroscience Reviews VOLUME 5, 565-575 2004

Pain Pathways

Types of Pain Relief Intervention

Social Rejection Activates Brain Regions for Affective Pain

Placebo effects terminology

• Placebo is Latin for “I will please”• An inert substance or treatment that does not have a

direct physiological effect – The original meaning: 1950: The effect of a placebo treatment – The alternative meaning: 1960-80: The effect of the interaction

between the patient and the health provider

• Belief in the beneficial nature of the treatment• a key component of the true placebo effect• enhanced by factors such as

• interaction with the physician• sensory impact of the treatment

• Negative beliefs can generate a nocebo effect• may explain some psychogenic illnesses• basis of much research in psychoneuroimmunology

Placebo Effects• Placebos have effect on

– subjective and objective outcomes– in a large proportion of patients– with a wide range of clinical conditions such as

• Pain• Asthma• Survival after myocardial infarction• Hypertension• Colds

• Used in research trials to objectively test the efficacy of new treatments

• One group is given the treatment, while another group (the control group) receives a placebo

• Comparing the results from both groups should reveal the effects of the treatment

Placebo Response Mechanisms• Examples of pain relief “analgesia” from placebo• Expectation “belief” in treatment• Activation of opiate based descending control system

– 30 – 50 % get some analgesia

– can be blocked by naloxone an opiate antagonist

• Expectation produces increased activity during anticipation of pain in the prefrontal cortex

• Decreased activity in the thalamus, insula, and anterior cingulate cortex

• Probably a frontal cortex activation of areas in the cingulate cortex which then activates the PAG midbrain areas

Placebo Response Mechanisms• Expectation from:

– Conditioning: previously experiencing the benefit – Social learning: observing others produces similar placebo

responses to conditioning– Verbal suggestions: alone produces smaller effects

• Problem of no “untreated”control group – effect consists of two components– nonspecific effects (eg, natural recovery)– a "true placebo effect" that is the psychological therapeutic

effect of the treatment– So effect of placebo is not isolated from

• spontaneous remission• regression to the mean• other factors