Little Background

Pain is such a small word but it carries an enormous amount of weight in both our physical and physiological world. It is something that everyone experiences. While trying to better understand some aspects of pain; I started to put together a storyboard. I quickly realized, the story of pain is extremely difficult with its endless twists and turns. Nonetheless, I decided to at least start the story and share some of my illustrations and experiments with different illustration/web techniques.

Thank you for visiting!

- Laura Johnston

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Pain

An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
International Association for the Study of Pain IASP

Defining Pain

Hyperalgesia
Disproportionate hypersensitivity to stimuli; increase feeling of pain from something that would normally cause pain; increase response

Allodynia
Nociceptive responses to non-noxious stimuli; stimulus creating a sensation of pain which normally would not provoke pain

Hyperpathia
Pins-and-needles or electric-shock-like sensations; abnormal reaction to stimulus

Chronic pain
Pain that persists over a long period of time which started due to an injury or ongoing cause - disease

Neuropathic pain
Pain caused by a lesion or disease of the somatosensory nervous system (sensory system)

Based on International Association for the Study of Pain and NIH Medline Plus

Pain Pathway

Pain PathwayActionmotorneuronsFlexor reflex,withdrawalresponseOrganizeNeurons synapsis occurin the thalamus (brain) PerceptionSensory cortexActionMotor cortexAscending pathway(anterolateral system orspinothalamic tract)Created by Laura A. Johnston © Nova Scotia Canada laura@petitegraphics.comDescendingpathway Impulses along axonsInterpretationDorsal hornin the spinal cordPainsite of originSensory neurons

Nerves - Neurons

There are three types of neurons, all of which play important roles in pain transmission and reaction(s):

Peripheral Nervous System: Allows for reaction to physical environment.

Nociceptor environmental stimuliNociceptorNociceptorEnvironmental stimuli(mechanical, thermo, or chemical)Created by Laura A. Johnston © Nova Scotia Canada laura@petitegraphics.com

Nociceptors

Free nerve ending - innervate skin, muscle, or organs

nociceptors basic morphologyCreated by Laura A. Johnston © Nova Scotia Canada laura@petitegraphics.comCentral axonPeripheral axon regionNociceptors/central/presynaptic terminalCell body (soma) in the DRGPeripheral terminalfree nerve endings, no myelin sheathAxon A B C D F E
  1. Axon
  2. Cell body (soma) in the DRG
  3. Nociceptors/central/presynaptic terminal
  4. Peripheral terminal; free nerve endings, no myelin sheath
  5. Peripheral axon region
  6. Central axon

Nociceptors are pseudounipolar nerve cells,both terminals can send and receive signals (neurotransmmiters, pH changes, & etc.)

NociceptorSecond-order neurons

The external noxious stimuli are transduced-translated by the nociceptor into electrical signals. The activation of the nociceptor depends on adquate external stimuli, location of the nociceptor, and type of stimuli.

Nociceptors can respond to mechanical (pressure or mechanical deformation), thermal and/or chemical noxious stimuli brought on by damage, abnormal cell growth, and/or inflammation. Nociceptors are generally categorized as thermal, mechanical, chemical, polymodal; respond to multiple types of stimuli, and silent/sleeping; normally unresponsive but become responsive after tissue injury/inflammation occurs.

Cross Section

Representative cross section of the neuron

Cross section neuronsCreated by Laura A. Johnston © Nova Scotia Canada laura@petitegraphics.comaxonmyelin

*Involved in pain C and Aδ (A-delta)

In some cases Aβ can be stimulated by high threshold stimuli

Nociceptor Aδ Fibers

A delta fibers are lightly myelinated and are faster in the conduction of pain signal; normally associated with sharp pain

layers of myelinNode of RanvierSpace in betweenMyelinated: a Schwann cellmakes up the myelin sheathaxonSchwann cell nucleuscross sectionSchwann cell, wraps around the axonABCDEF
  1. Node of Ranvier - Space in between
  2. Myelinated: a Schwann cell makes up the myelin sheath
  3. Cross section
  4. Axon
  5. Layers of myelin myelin
  6. Schwann cell nucleus; Schwann cell, wraps around the axon

Nociceptor C Fibers

Unmyelinated
Most nociceptors are unmyelinated, C fibers (slow); normally associated with dull ache, second-order pain sensation.

C fibersRemak bundlesUnmyelinated Schwann cells can surround (ensheath) several c-fibers; bundling them togetherACreated by Laura A. Johnston © Nova Scotia Canada laura@petitegraphics.com

A Unmyelinated Schwann cells can surround bundle(ensheath) several c-fibers cfiber; bundling them together.

C fibers can be subclassified:

It is important to note that recent studies would suggest further classifications of nociceptors based on transcriptomic, morphological and funcational characteristics.

© Laura A. Johnston - Petite Graphics 2018 Nova Scotia Canada

Creative Commons License Images (except photographs) were created by Laura Johnston and are licensed under a creative commons.