Somatosensory Science Facts

By Charles Pidgeon, PhD and Sehej Bindra

Tactile sensations are well studied, and much is known about this sensory system. The complexity is difficult to learn because of the breadth of information available. The approach of this book was to inform interested readers about this system through questions and answers. For instance, understanding the science causing people not to be able to tickle themselves is insightful. There are approximately 200 questions and answers for the reader to think about on their own pace. Questions include a thorough description of Sensory Systems, Sensory Receptors, Cognitive and Cortical processing, Stimuli (pain, heat, pleasure, etc.), Meditation and brain Waves, Social Behavior, and much more.

• Language: English
• Publisher: MainspringBooks
• Release date: Nov 12, 2021
• ISBN: 9781641336420

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Copyright © 2021 by Charles Pidgeon, Ph.D.

All rights reserved. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author, except in the case of brief quotations embodied in critical reviews and certain other noncommercial uses permitted by copyright law.

Printed in the United States of America

ISBN 978-1-64133-640-6 (paperback)

ISBN 978-1-64133-641-3 (hardback)

ISBN 978-1-64133-642-0 (ebook)

Library of Congress Control Number : 2021905704

MainSpring Books

5901 W. Century Blvd

Suite 750

Los Angeles, CA, US, 90045

www.mainspringbooks.com

Dedicated to Timothy Steven Pidgeon, he touches my mind every time we talk

List of Contributors

Sehej Bindra

West Windsor-Plainsboro High School North, Class of 2020

Rishi Patel

West Windsor-Plainsboro High School North, Class of 2021

Keshav Ratra

West Windsor-Plainsboro High School North, Class of 2021

David Pan

West Windsor-Plainsboro High School North, Class of 2021

Ria Verma

West Windsor-Plainsboro High School North, Class of 2022

Olivia Tang

West Windsor-Plainsboro High School North, Class of 2023

Josephine Wang

West Windsor-Plainsboro High School North, Class of 2023

Arnav Rastogi

West Windsor-Plainsboro High School North, Class of 2020

Yash Gupta

West Windsor-Plainsboro High School North, Class of 2019

Table of Contents

List of Contributors

Preface

Introduction

General Neuroscience

1 Neurons

2 Nerves

3 Sensory Receptors & Fibers

4 Spinal Pathways

5 Cortex

6 Interconnectedness of Sensations

Sensation

1 Touch and Pressure

2 Pain

3 Temperature

4 Proprioception & Sensorimotorics

5 Vibration

Cognition and Cortical Circuitry

1 Embodied Cognition

2 Pleasure

3 Meditation and Brain Waves

4 Social Behavior

Glossary

Index

Preface

The somatosensory system is often taught with a focus on its theoretical aspects. Somatosensory Science Facts attempts to not only cover the basics of how the somatosensory system works but to also integrate such theory to allow the reader to paint a tangible picture of how such small physiological processes interact, allowing an individual to make sense of the world that surrounds them. This book will explain basic somatosensory neuroscience theory and then expand on these fundamental concepts through applying them in the context of experimental research and day-to-day life.

Through the question and answer format, this book does not simply layout information on the somatosensory system. Rather, Somatosensory Science Facts delves into interesting questions on the sensory system and makes connections between the theory and the research. Readers are guided to think about the somatosensory system not just as an accumulation of inarguable facts, but as a science: a dynamic field of questions, experiments, and arguments.

Part I lays the foundation of general neuroscience concepts that the reader needs to comprehend to understand somatosensory processes. Part II discusses each somatosensation separately through exploring the physiology of each sensation and its applications. Part III explains the often overlooked relationship between cognition and the body senses through discussing the connection between the somatosensory system and topics such as embodied cognition, pleasure, mindful meditation, and social touch.

This book explains difficult concepts and studies in accessible terms and highlights important concepts and key takeaways from studies. For readers interested in learning more about the topic and specific results or methods that may be overlooked in the book, they may access the references linked right below each question. References primarily consist of a published article from an accredited journal. Thus, Somatosensory Science Facts can be used by anyone despite their background, ranging from students to professionals to just anyone interested in learning neuroscience.

A Few Examples:

Why do limbs fall asleep?

What is the first sense that developed in animals?

How does the high number of genes in human cells contribute to mechanoreceptor diversity?

What is the difference between encapsulated and unencapsulated mechanoreceptors?

Why are C fibers unmyelinated?

Why do reflexes not go through the brain?

What is neuroplasticity?

What is the cutaneous rabbit illusion?

What effect does touch have on brain dopamine levels?

Why can’t someone tickle themselves?

Why do loud sounds make one’s ear hurt?

What is the role of the insula in pain processing?

Are spicy foods actually hot?

What is the purpose of random movements or twitching during sleep?

Why can individuals physically feel bass in songs?

Why do phantom phone vibrations occur?

Can emotions change one’s perception of pain?

Can shamanic healing alleviate pain?

What are some arguments against the existence of embodied cognition?

Why do massages feel pleasurable?

How does pain influence pleasure?

How does mindful meditation improve one’s health through the somatosensory system?

Can touch influence first impressions of others?

Introduction

Whether it is feeling the soft feathers of a pigeon, the cold wintery air, or the movement of your own arm, the somatosensory system allows us to use our periphery to understand our external and internal environments. Specifically, the somatosensory system is responsible for the perception of touch, vibration, pressure, pain, temperature, and self-movement through sensory receptors located in the skin, muscles, tendons, and joints.

There is a diverse array of sensory receptors in the somatosensory system that are each responsible for detecting a distinct component of the environment. Meissner’s corpuscles are sensory neurons that allow you to perceive subtle tactile details through its ability to sense light pressure, fine touch, and low-frequency vibration. Similarly, Merkel discs aid in sensing light touch; however, because they adapt slowly to stimuli, they have a slightly different function than Meissner’s corpuscles. Pacinian corpuscles, on the other hand, are located deeper in the skin and detect strong pressure and high-frequency vibrations. Next, we have Krause end bulbs that detect cold temperatures and Ruffini ends that sense skin stretch, sustained pressure, and warmth. If any stimuli are present in excess, whether mechanical or thermal, a class of sensory receptors known as nociceptors elicits painful sensations. Finally, proprioceptors located in muscles, tendons, and joints allow individuals to understand the movement and orientation of body parts relative to each other.

This diverse assortment of receptors in the skin then relays somatosensory information through spinal pathways, sequences of neurons that connect the body to the brain through traversing the spinal cord. Each somatosensation has an associated pathway that consists of different fibers going to different regions of the nervous system. For instance, the spinothalamic tract, which relays sensory information regarding pain and temperature, uses myelinated A and unmyelinated C fibers that reach the dorsal portion of the spinal cord. From there, axons cross over to the opposite side of the spinal cord, enter the brainstem, and finally terminate on to a specific nucleus in the thalamus. On the other hand, the PCML pathway, responsible for fine touch, proprioception, vibration, and pressure, travels up the dorsal column of the spinal cord to the brainstem and also crosses over to the other half of the spinal cord. The pathway then connects to a different thalamic nucleus than that of the spinothalamic tract, and finally terminates in the somatosensory cortex.

The primary somatosensory cortex is a region in the postcentral gyrus of the parietal lobe that receives somatosensory information. This cortical region is responsible for the initial processing of touch, pain, vibration, and pressure. Next, associated regions such as the secondary somatosensory cortex regulate tactile attention and pain. Additional regions like the anterior cingulate cortex and insula interpret sensory information through higher cognitive processes such as assigning emotions to somatosensory stimuli.

Somatosensory information processed in the brain is not only important for you to perceive your physical environment, but is also deeply rooted in higher brain function. In fact, the relationship between cognition and sensations is bidirectional: cognition can influence somatosensations and vice versa. One example of the former is the observation that when feeling anxious, the magnitude of pain brought on by a stimulus is amplified. On the other hand, physical stimuli, such as being touched by another individual, can influence your cognitive state by eliciting strong emotions. The close relationship between sensation and cognition demonstrates that the somatosensory system is not simply a conglomeration of molecular mechanisms and neural pathways, but rather is essential to how we understand and respond to our environment.

Questions

Part I: General Neuroscience

Neurons

What are neurons?

What is gray and white matter?

What are the different structural classes of neurons?

What are the different functional classes of neurons?

How do neurons receive signals?

What are neurotransmitters?

What is myelin?

What arespindle neurons?

What are pyramidal neurons?

What is neuroimaging?

Nerves

How is the nervous system organized in the body?

What are the nerves?

Why do limbs fall asleep?

What is Carpal Tunnel Syndrome?

What are cranial nerves?

What is the trigeminal nerve?

What are the trigeminal nuclei?

What is a neck-tongue syndrome?

Sensory Receptors & Fibers

What is the somatosensory system?

What are sensory receptors?

What specific receptors are involved in the somatosensory system?

What is the difference between tonic and phasic receptors?

How are different cells able to express a diverse array of different receptors?

What is the difference between encapsulated and unencapsulated mechanoreceptors?

What are receptive fields?

What are the types of sensory fibers?

Why are C fibers unmyelinated?

Spinal Pathways

What is the spinal cord?

What major spinal pathways are important for somatosensory transmission?

What is the spinothalamic pathway?

What is the posterior column-medial lemniscus pathway?

What is the extrapyramidal system?

What is the corticospinal pathway?

What is the bulbospinal pathway?

What is Cauda Equina Syndrome?

What are reflexes and what is the reflex arc?

Why do reflexes not go through the brain?

What is the knee-jerk reaction?

Cortex

What is the cortex?

What cortical locations are relevant to the somatosensory system?

What is the primary somatosensory cortex?

What is the secondary somatosensory cortex?

What is neuroplasticity?

Interconnectedness of Sensations

What is Synesthesia?

Does color-touch synesthesia exist?

What somatosensory processes are involved in itching and tickling?

What is haptic perception?

What are haptic memories?

What is Molyneux’s problem?

Why do fingers wrinkle when exposed to water for long periods of time?

Part II: Sensation

Touch and Pressure

What is the evolutionary importance of touch?

What are the types of tactile receptors and where are they located?

What is a Meissner’s corpuscle and how does its structure aid its function?

What is a Merkel Cell and how does its structure aid its function?

What is a Pacinian corpuscle and how does its structure aid its function?

What is a Ruffini Ending and how does its structure aid its function?

What are the types of tactile channels?

What is the touch homunculus?

What is the two-point discrimination test?

What is a grating orientation task?

Can humans feel stimuli as small as bacteria?

How can one determine the material of an object through touch?

What is fine and crude touch?

What is the role of the primary somatosensory cortex in tactile perception?

What is the cutaneous rabbit illusion?

What is the role of the secondary somatosensory cortex in tactile perception?

What is the role of the insula in tactile perception?

What is the role of oxytocin in tactile perception?

What effect does touch have on brain dopamine levels?

How does touch affect body serotonin levels?

How is the perception of stickiness produced?

What is the role of the cerebellum in tactile perception?

Why can’t someone tickle themself?

How does a stroke affect touch sensation?

How does the body respond to noxious tactile stimuli?

How does one sense something in their nose?

How does one feel the wind blowing across their hair?

Why does one not feel makeup on his or her face after a long day wearing it?

How does the body respond to being massaged?

What is tadoma?

What are tactile hallucinations?

What are corns and calluses?

What is habituation?

How are humans able to approximate the speed of a moving object simply by touching the object?

What effect do hormones have on the sense of touch?

How do opioids and endorphins influence tactile perception?

What is a somatosensory evoked potential test?

How do skin burns affect the tactile senses?

How does peripheral neuropathy affect tactile sensation?

How does being blind influence tactile perception?

Does race influence tactile perception?

How does gender influence tactile perception?

How does aging influence tactile perception?

What are some differences in tactile perception between humans and other animals?

How does tactile sensation in robotic sensors compare to humans?

How does a touch screen laptop work?

How do touch screen gloves work?

While asleep, why are touch stimuli particularly effective in awakening humans?

Pain

What is pain?

What is nociception?

What are nociceptors?

Where are nociceptors located?

How do nociceptors interact with other mechanoreceptors?

What is substance P?

Which sensory systems are involved in a sunburn?

What happens when a highly concentrated acidic or basic solution splashes onto one’s arm?

How can overstretch elicit pain?

Why do loud sounds make one’s ear hurt?

How are some people able to firewalk without feeling intense pain?

Why are migraines painful?

Why does a brain freeze hurt?

Why do closed fractures hurt?

Why do vaccines hurt one day after the delivery?

What pathways are responsible for regulating pain?

What are some theories on how pain is transmitted?

What is a herniated disk and how does it cause pain?

What is referred pain?

How does the brain process pain?

What is the role of the insula in pain processing?

What is the role of the cingulate cortex in pain processing?

How are pleasure circuits involved in the body’s response to pain?

What is duloxetine and how does it work?

How does capsaicin influence pain perception?

How do opioids and endorphins influence pain perception?

Why does hydrogen peroxide sting when rinsing one’s mouth with it?

What is acupuncture and how does acupuncture influence pain perception?

How does obesity influence pain perception?

What is the μ-opioid receptor system?

What causes an itching sensation?

Why does scratching an itch provide satisfaction?

What is phantom limb pain?

What is mirror box therapy?

How does sleep loss influence pain perception?

Temperature

What are thermoreceptors?

How do thermoreceptors aid in temperature regulation?

How do cold temperatures cause one to shiver?

Why does one feel shivery and cold in a scary situation?

Why do hands and feet get numb after being exposed to cold for an extended period of time?

Why might one feel slightly cold when touching something that is really hot?

Are spicy foods actually hot?

What spinal pathways are relevant for thermoreception?

How is the body capable of quickly retreating upon exposure to an extremely hot surface?

What brain regions are relevant for thermoreception?

How does temperature alter the sleep patterns of an individual?

Proprioception & Sensorimotorics

What is kinesthesis?

What parts of the body are responsible for kinesthesis?

What is proprioception?

What general pathways are responsible for proprioception?

How does alcohol affect proprioception?

How does synesthesia influence proprioception?

What is muscle memory and how is it developed?

What is the vestibular system?

How are people able to maintain balance?

What is the role of the cerebellum in balance?

What general pathways are responsible for vestibulation?

What are hair cells?

What causes motion sickness?

What is Ménière’s disease?

What is the purpose of random movements or twitching during sleep?

Vibration

What mechanoreceptors are responsible for sensing vibration?

What stimuli generate a sensation of vibration?

Why can individuals physically feel bass in songs?

Why do phantom phone vibrations occur?

What spinal pathways are responsible for vibration?

How does subtle vibration affect sleep quality?

Part III: Cognition and Cortical Circuitry

Embodied Cognition

What is cognition?

What are modal and amodal theories of mental representation?

What is embodied cognition?

What is the replacement hypothesis?

What is the gesture-for-conceptualization hypothesis?

What is the Macbeth effect?

What is psychological priming?

How are somatosensory brain regions involved in embodied cognition?

Can emotions change one’s perception of pain?

Can shamanic healing alleviate pain?

What are the similarities and differences between psychological and physical pain?

How does cognition influence the sensation of pain?

What are some arguments against the existence of embodied cognition?

Pleasure

What is pleasure?

What brain mechanisms lead to reward associated with pleasure?

What are the roles of different neurotransmitters in the brain in the sensation of