Touch and Pain

Module 20: The Sense of Touch and Pain

• Overview of Touch Sensations

  • The sense of touch comprises four basic distinct skin sensations:

  • Pressure

  • Warmth

  • Cold

  • Pain

  • Other skin sensations are variations of these four basic sensations.

• Cortex Response

  • Touch sensations involve different responses in the somatosensory cortex located in the parietal lobes.

  • These responses illustrate the influence of cognition on sensory response, emphasizing top-down processing.

Experience of Pain

• Definition of Pain

  • Pain serves as the body's alert mechanism indicating something has gone wrong.

  • It reflects both bottom-up sensations and top-down cognition.

• Influences on Pain Perception

  • The perception of pain is affected by biological, psychological, and sociocultural influences.

  • Individual pain thresholds vary significantly from one person to another (e.g., some have high pain thresholds while others have low).

• Personal Experience of Pain

  • Consideration of how individuals cope with pain is essential.

  • Factors influencing personal pain experiences include:

  • Biological influences

  • Psychological influences

  • Sociocultural influences

Biological Influences on Pain

• Neural Activity and Endorphins

  • Spinal cord activity in large and small fibers affects pain perception.

  • Differences in endorphin production can influence pain experiences.

  • The brain interprets central nervous system (CNS) activity in varied ways.

Psychological Influences on Pain

• Attention and Expectations

  • Focusing on pain can heighten perceptions of it.

  • Experience and anticipation of pain, such as at the dentist, greatly influence perception.

Sociocultural Influences on Pain

• Cultural Practices

  • Pain expression can vary based on social situations and cultural upbringing (e.g., silent childbirth practices).

  • Empathy may influence personal pain experiences and how one responds to the pain of others.

Pain Mechanism

• Pain Circuit

  • Nociceptors are sensory receptors that respond to potentially damaging stimuli (e.g., stepping on a tack).

  • Pain signals travel through the spinal cord, passing through the nociceptor's cell body and interneurons before reaching the brain.

• Gate Control Theory

  • The theory posits that the spinal cord contains a neurological gate that controls pain transmission.

  • Most pain signals are received through small spinal cord nerve fibers, while large fiber activity can close pain gates by blocking these signals.

  • Additional gate-closing methods include pain modulation messages from the brain to the spinal cord, potentially alleviating pain sensations.

• Endorphin Release

  • Endorphins act as natural painkillers released during severe pain or physical activity (e.g., exercise may lead to a "runner's high").

  • In childbirth, endorphin release can lead to reduced pain perception near the end of labor.

Clinical Practices for Pain Management

• Practical applications for controlling pain can include:

  • Medications (drugs)

  • Surgical interventions

  • Acupuncture and electrical stimulation

  • Massage and exercise

  • Psychological techniques, such as hypnosis and relaxation training

  • Distraction techniques (placing mental focus elsewhere)

  • Placebo interventions which can alter CNS attention and response to pain

Chemical Senses

Taste and Smell

Taste

• Basic Sensations

  • Taste is categorized into several sensations:

  • Sweet

  • Sour

  • Salty

  • Bitter

  • Umami (added later to describe savory tastes)

  • Taste receptors react to specific food molecules and send messages to the brain.

• Survival Functions of Taste

  • Displeasure from sour or bitter tastes can signal toxicity.

  • Sweet tastes are generally associated with high-calorie, non-toxic food sources which enhance survival.

Smell

• Chemical Sensation of Smell

  • Odor molecules can vary greatly, requiring multiple receptors for detection.

  • Smells are processed in the olfactory cortex and intertwined with memory and emotion through their connections to the limbic system.

  • Gender, age, and expertise can influence scent identification capabilities.

Olfactory Process

• Mechanism

  • Odorous molecules activate olfactory receptors in the nose, sending signals to the olfactory bulb (directly connected to the brain).

  • The olfactory bulb bypasses the thalamus before reaching the primary smell cortex located between the frontal and temporal lobes, explaining rapid odor perception.

Body Senses

Kinesthesia and Vestibular Sense

• Definition of Kinesthesia

  • Kinesthesia detects the position and movement of individual body parts; relies on interaction with vision.

• Vestibular Sense

  • This sense helps maintain balance and body orientation.

  • Active proprioceptors in muscles, tendons, and joints provide feedback to the brain about body position.

Example in Sports

• Simone Biles Case

  • During the 2020 Tokyo Olympics, Biles withdrew due to experiencing 'the twisties', a state where she lost awareness of her body position in space, linked to vestibular dysfunction.

Sensory Interaction

• Interdependence of Senses

  • Sensory systems are not isolated; they interact extensively (e.g., taste and smell).

  • Sensory interaction can enhance experiences such as flavor, where smell and taste work together.

Perception Without Sensation

• Extrasensory Perception (ESP)

  • Claims that perception can occur without sensory input, involving phenomena like telepathy, clairvoyance, and precognition.

  • Critiques of ESP arise from methodological flaws observed in experimental studies such as those by BEM, who proposed anticipatory abilities.

  • Continual skepticism from scientific communities regarding the validity of ESP claims remains a prominent attitude.

• Conclusion

  • The chapter closes with reflections on individual skepticism and personal beliefs regarding the interconnectedness of perceived sensations and cognitive processes.